Bacillus Lentus Alkaline Protease Variants With Increased Stability

1. Field of the Invention

This invention relates to mutant proteolytic enzymes having improved properties relative to the wild-type enzyme, to genetic constructs which code for the mutant proteolytic enzymes, to methods of predicting mutations which enhance the stability of the enzyme, and to methods of producing the mutant proteolytic enzymes.

2. Description of the Related Art

Subtilisins are a family of extracellular proteins having molecular weights in the range of 25,000-35,000 daltons and are produced by various Bacillus species. These proteins function as peptide hydrolases in that they catalyze the hydrolysis of peptide linkages in protein substrates at neutral and alkaline pH values. Subtilisins are termed serine proteases because they contain a specific serine residue which participates in the catalytic hydrolysis of peptide substrates. A subtilisin enzyme isolated from soil samples and produced by Bacillus lentus for use in detergent formulations having increased protease and oxidative stability over commercially available enzymes under conditions of pH 7 to 10 and at temperature of 10 to 60.degree. C. in aqueous solutions has been disclosed in copending patent application Ser. No. 07/398,854, filed on Aug. 25, 1989. This B. lentus alkaline protease enzyme (BLAP, vide infra) is obtained in commercial quantities by cultivating a Bacillus licheniformis ATCC 53926 strain which had been transformed by an expression plasmid which contained the wild type BLAP gene and the B. licheniformis ATCC 53926 alkaline protease gene promoter.

Industrial processes generally are performed under physical conditions which require highly stable enzymes. Enzymes may be inactivated by high temperatures, pH extremes, oxidation, and surfactants. Even though Bacillus subtilisin proteases are currently used in many industrial applications, including detergent formulations, stability improvements are still needed. Market trends are toward more concentrated detergent powders, and an increase in liquid formulations. Increased shelf stability and oxidative stability, with retention of catalytic efficiency are needed. It is therefore desirable to isolate novel enzymes with increased stability, or to improve the stability of existing enzymes, including subtilisin proteases such as BLAP.

The stability of a protein is a function of its three dimensional structure. A protein folds into a three dimensional conformation based upon the primary amino acid sequence, and upon its surrounding environment. The function and stability of a protein are a direct result of its three dimensional structure.

A large body of information has been published which describes changes in enzyme properties as a result of alterations in the primary amino acid sequence of the enzyme. These alterations can result from random or site specific alterations of the gene which expresses the enzyme using genetic engineering techniques. Random approaches mutagenize total cellular DNA, followed by selection for the synthesis of an enzyme with improved properties. This approach requires neither knowledge of the three dimensional structure of the enzyme, nor any predictive capability on the part of the researcher. Site directed mutagenesis, on the other hand, requires a rational approach for the introduction of amino acid changes. In this approach one or more amino acids may be replaced by other residues by altering the DNA sequence which encodes the protein. This can be accomplished using oligonucleotide directed in vitro mutagenesis. The following references teach site-directed mutagenesis procedures used to generate specific amino acid substitution(s): Hines, J.C., and Ray, D.S. (1980) Gene 11:207-218; Zoller, M.J., and Smith, M. (1982) Nucleic Acids Res. 10:6487-6500; Norrander, J., et al. (1983) Gene 26:101-106; Morinaga, Y., et al. (1984) Bio/Technology 2:636-639; Kramer, W., et al. (1984) Nucleic Acids Res. 12:9441-9456; Carter, P., et al. (1985) Nucleic Acids Res. 13:4431-4443; Kunkel, T.A. (1985) Proc. Natl. Acad. Scio USA 82:488-492; Bryan, P., et al. (1986) Proc. Natl. Acad. Sci. USA 83:3743-3745.

A rational approach may or may not require knowledge of a protein's structure. For example, patent application WO 89/06279 describes the comparison of the primary amino acid sequence of different subtilisins while contrasting differences in physical and chemical properties. The primary amino acid sequences of the different subtilisins are aligned for the greatest homology, while taking into account amino acid insertions, deletions, and total number of amino acids.

Currently, the amino acid sequences of at least 10 subtilisin proteases have been published. Eight of these subtilisins were isolated from species of Bacilli, and include subtilisin 168 (Stahl, M.L., and Ferrari, E. (1984) J. Bacteriol. 158:411-418), subtilisin BPN' (Vasantha, N., et al., (1984) J. Bacteriol. 159:811-819), subtilisin Carlsberg (Jacobs, M., et al. (1985) Nucleic Acids Res. 13:8913-8926), subtilisin DY (Nedkov, P., et al. (1985) Biol. Chem. Hoppe-Seyler 366:421-430), subtilisin amylosacchariticus (Kurihara, M., et al. (1972) J. Biol. Chem. 247:5619-5631), subtilisin mesenticopeptidase (Svendsen, I., et al. (1986) FEBS Lett. 196:228-232), subtilisin 147 and subtilisin 309 (Hastrup et al. (1989) WO 9/06279), subtilisin PB92 (Van Eekelen et al. (1989) EP 328229), and subtilisin BLAP (Ladin, B., et al. (1990) Society for Industrial Microbiology Annual Meeting, Abstract P60). The remaining two subtilisin sequences are thermitase from the fungus Thermoactinomyces vulgaris (Meloun, B., et al. (1985) FEBS Lett. 183:195-200), and proteinase K from the fungus Tritirachium album limber (Jany, K.-D., and Mayer, B. (1985) Biol. Chem. Hoppe-Seyler 366:485-492).

Methods for obtaining optimum alignment of homologous proteins are described in Atlas of Protein Sequence and Structure, Vol. 5, Supplement 2 (1976) (Dayhoff, M.O., ed., Natl. Biomed. Res. Found., Silver Springs, Md.). This comparison is then used to identify specific amino acid alterations which might produce desirable improvements in the target enzyme. Wells, J.A., et al. (1987) Proc. Natl. Acad. Sci. USA 84:1219-1223, used primary sequence alignment to predict site directed mutations which affect the substrate specificity of a subtilisin. Using the alignment approach WO 89/06279 teaches the construction of mutant subtilisins having improved properties including an increased resistance to oxidation, increased proteolytic activity, and improved washing performance for laundry detergent applications. Patent applications WO 89/09819, and WO 89/09830 teach improvement in the thermal stability of subtilisin BPN' by the introduction of one or more amino acid changes based on the alignment of the primary amino acid sequences of subtilisin BPN' with the more thermal stable subtilisin Carlsberg. From hereon, amino acids will be referred to by the one or three letter code as defined in Table 1.

A=Ala=Alanine

C=Cys=Cysteine

D=Asp=Aspartic acid or aspartate

E=Glu=Glutamic acid or glutamate

F=Phe=Phenylalanine

G=Gly=Glycine

H=His=Histidine

I=Ile=Isoleucine

K=Lys=Lysine

L=Leu=Leucine

M=Met=Methionine

N=Asn=Asparagine

P=Pro=Proline

Q=Gln=Glutamine

R=Arg=Arginine

S=Ser=Serine

T=Thr=Threonine

V=Val=Valine

W=Trp=Tryptophan

Y=Tyr=Tyrosine

Rational mutational approaches may also predict mutations which improve an enzyme property based upon the three dimensional structure of an enzyme, in addition to the alignment of primary amino acid sequences described above. One method for determining the three dimensional structure of a protein involves the growing of crystals of the protein, followed by X-ray crystallographic analysis. This technique has been successfully used to determine several high resolution subtilisin structures such as thermitase (Teplyakov, A.V., et al. (1990) 214:261-279), subtilisin BPN' (Bott, R., et al. (1988) J. Biol. Chem. 263:7895-7906) and subtilisin Carlsberg (Bode, W., et al. (1986) EMBO J. 5:813-818), for example.

EP 0251446 teaches the construction of mutant carbonyl hydrolases (proteases) which have at least one property different from the parental carbonyl hydrolase. It describes mutations which effect (either improve or decrease) oxidative stability, substrate specificity, catalytic activity, thermal stability, alkaline stability, pH activity profile, and resistance to autoproteolysis. These mutations were selected for introduction into Bacillus amyloliquefaciens subtilisin BPN' after alignment of the primary sequences of BPN' and proteases from B. subtilis, B. licheniformis, and thermitase. Such alignment can then be used to select amino acids in these other proteases which differ, as substitutes for the equivalent amino acid in the B. amyloliquefaciens carbonyl hydrolase. This application also describes alignment on the basis of a 1.8 .ANG. X-ray crystal structure of the B. amyloliquefaciens protease. Amino acids in the carbonyl hydrolase of B. amyloliquefaciens which when altered can affect stability, substrate specificity, or catalytic efficiency include: Met50, Met124, and Met222 for oxidative stability; Tyr104, Ala152, Glu156, Gly166, Gly169, Phe189, and Tyr217 for substrate specificity; N155 alterations were found to decrease turnover, and lower Km; Asp36, Ile 107, Lys170, Asp197, Ser204, Lys213, and Met222 for alkaline stability; and Met199, and Tyr21 for thermal stability. Alteration of other amino acids was found to affect multiple properties of the protease. Included in this category are Ser24, Met50, Asp156, Gly166, Gly169, and Tyr217. Substitution at residues Ser24, Met50, Ile107, Glu156, Gly166, Gly169, Ser204, Lys213, Gly215, and Tyr217 was predicted to increase thermal and alkaline stability. An important point about this patent application is that with the exception of those mutations effecting substrate specificity, no rational mutational approach for improving the alkaline or temperature stability of a protease based upon computer simulations of an X-ray crystal structure is described.

WO 88/08028 teaches a method for redesigning proteins to increase stability by altering amino acid residues that are in close proximity to the protein's metal ion binding site. This application describes the alteration of a calcium ion binding site present within subtilisin BPN' through the substitution, insertion, or deletion of amino acid residue(s) in close proximity to that site so that the electrostatic attraction between the amino acids and the calcium ion is increased. The characterization of the calcium ion binding site is accomplished through the analysis of a 1.3 .ANG. three dimensional structure of subtilisin BPN' using a high resolution computer graphics system. This approach allows the selection of amino acids acceptable for replacing the native amino acids in the protease by first simulating the change using the computer model. This allows for the identification of any problems including steric hindrance prior to the actual construction and testing of the mutant proteases.

U.S. Pat. Nos. 4908773 and 4853871 teach a computer based method for evaluating the three dimensional structure of a protein to select amino acid residues where the introduction of a novel disulfide bond will potentially stabilize the protein. Potentially acceptable amino acid residues can then be ranked, and replaced using computer simulation, prior to the actual construction of the mutant protein using site directed mutagenesis protocols.

Several patent applications combine published data on biochemical stability with computer analysis of three dimensional protease structures in order to predict mutations which stabilize the enzyme. U.S. Pat. No. 4,914,031 and WO 88/08033 and WO 87/04461 teach a method for improving the pH and thermal stability of subtilisin aprA by replacing asparagine residues present in asparagine/glycine pairs. Asparagine/glycine pairs in proteins have been shown to undergo cyclization to form cyclic imide anhydroaspartylglycine (Bornstein, P., and Balian, G. (1977) Methods Enzymol. 47:132-145). This cyclic imide is susceptible to base hydrolyzed cleavage leading to inactivation of the enzyme. Computer analysis of the three dimensional structure of the aprA protease also predicted that formation of the cyclic imide could lead to protease inactivation resulting from a shift of the side chain of the active site serine. The decision to replace the asparagine residue and not the glycine residue was based upon alignment of the aprA sequence with other subtilisin-like enzymes, cucumisin and proteinase K.

Sensitivity to oxidation is an important deficiency of serine proteases used in detergent applications (Stauffer, C.E., and Etson, D. (1969) J. Biol. Chemo 244:5333-5338). EP 0130756, EP 0247647, and U.S. Pat. No. 4,760,025 teach a saturation mutation method where one or multiple mutations are introduced into the subtilisin BPN' at amino acid residues Asp32, Asn155, Tyr104, Met222, Gly166, His64, Ser221, Gly169, Glu156, Ser33, Phe189, Tyr217, and/or Ala152. Using this approach mutant proteases exhibiting improved oxidative stability, altered substrate specificity, and/or altered pH activity profiles are obtained. A method is taught in which improved oxidative stability is achieved by substitution of methionine, cysteine, tryptophan, and lysine residues. These publications also teach that mutations within the active site region of the protease are also most likely to influence activity. Random or selected mutations can be introduced into a target gene using the experimental approach but neither EP 0130756, EP 0247647, nor U.S. Pat. No. 4,760,025 teach a method for predicting amino acid alterations which will improve the thermal or surfactant stability of the protease.

WO 8705050 teaches a random mutagenesis approach for construction of subtilisin mutants exhibiting enhanced thermal stability. One or more random mutations are introduced into single stranded target DNA using the chemical mutagens sodium bisulfite, nitrous acid, and formic acid. Subsequently, the mutated DNA is transformed into a Bacillus host and at least 50,000 colonies are screened by a filter assay to identify proteases with improved properties. Site directed mutagenesis can then be used to introduce all possible mutations into a site identified through the random mutagenesis screen. No method for pre selection of amino acids to be altered is taught.

EP 0328229 teaches the isolation and characterization of PB92 subtilisin mutants with improved properties for laundry detergent applications based upon wash test results. It teaches that biochemical properties are not reliable parameters for predicting enzyme performance in the wash. Methods for selection of mutations involve the substitution of amino acids by other amino acids in the same category (polar, nonpolar, aromatic, charged, aliphatic, and neutral), the substitution of polar amino acids asparagine and glutamine by charged amino acids, and increasing the anionic character of the protease at sites not involved with the active site. No method for identifying which specific amino acids should be altered is taught, and no rational mutational approach is taught which is based on alignment of X-ray structures of homologous proteases with different properties.

EP 0260105 teaches the construction of subtilisin BPN' mutants with altered transesterification rate/hydrolysis rate ratios and nucleophile specificities by changing specific amino acid residues within 15 .ANG. of the catalytic triad. Russell, A.J., and Fersht, A.R. (1987) Nature 328:496-500, and Russell, A.J., et al. (1987) J. Mol. Biol. 193:803-813, teach the isolation of a subtilisin BPN' mutant (D099S) that had a change in the surface charge 1415 .ANG. from the active site. This substitution causes an effect on the pH dependence of the subtilisin's catalytic reaction.

There are a number of different strategies for increasing protein stability. Many of these methods suggest types of substitutions to improve the stability of a protein but do not teach a method for identifying amino acid residues within a protein which should be substituted. From entropic arguments, many types of substitutions have been suggested such as Gly to Ala and any amino acid to Pro (Matthews, B.W., et al. (1987) Proc. Natl. Acad. Sci. 84:6663-6667). Likewise, while it is clear that increasing the apolar size of an amino acid in the core will add to stability, adverse packing effects may more than compensate for the hydrophobic effect, resulting in a decrease in protein stability (Sandberg, W.S., and Terwilliger, T.C. (1989) Science 245:54-57). Menendez-Arias, L., and Argos, P. (1990) J. Mol. Biol. 206:397-406, performed a statistical evaluation of amino acid substitutions of thermophilic and mesophilic molecules and proposed that decreased flexibility and increased hydrophobicity in the e-helical regions contributes most towards increasing protein stability. From their data, they formulated a set of empirical rules to improve stability.

Increasing the hydrophobicity of certain side chains has long been suggested as a means to improve protein stability. The hydrophobic exclusion of nonpolar amino acids is the largest force driving protein folding. This has been studied by examining the partitioning of amino acids or amino acid analogs from water to a hydrophobic medium. While the numbers vary depending on the work, these studies generally agree that burying a hydrophobic side chain increases protein stability. For example, 25 Kellis, J.T., Jr., et al. (1988) Nature 333:784-786, estimated that the removal of a methyl group destabilizes the enzyme by 1.1 kcal/mole assuming no other structural perturbations occur. Conversely, this predicts that the addition of a methylene group should add 1.1 kcal/mol if no unfavorable contacts occur. Similarly, Sandberg, W.S., and Terwilliger, T.C. (1989) Science 245:54-57, showed that the effect of removing or adding methylene groups is the sum of the hydrophobic effect and structural distortions. Simply adding buried hydrophobic groups may not increase protein stability because the total effect of adding or deleting a methyl group on the local packing structure must be considered. As the protein interior has a para-crystalline structure (Chothia, C. (1975) Nature 254:304-308), small distortions in the remainder of the structure resulting from the addition methyl group may exact a high cost and reduce rather than increase stability.

Along the same lines, the core of .lambda. repressor has been shown to be amazingly tolerant to apolar amino acid substitutions in a functional assay (Bowie, J.U., et al. (1990) Science 247:1306-1310). It is not clear that this is true for larger proteins. The constraints on the hydrophobic core of a small protein may be less stringent than a larger protein simply due to the volume of the core relative to the number of amino acids which need to pack into the region. As the volume of the hydrophobic core increases, the number of amino acids which must pack together correctly increases, requiring more specific nonlocal interactions.

It has been recognized that increasing the interior hydrophobicity of a protein as a means of increasing the stability is hampered by the difficulty of determining which positions in the protein will lead to stabilization when substituted (Sandberg, W.S., and Terwilliger, T.C. (1991) Trends Biotechnol. 9:59-63). The methods discussed above provide a means of determining what substitutions to make to improve stability but do not identify which sites in the protein are most important. The present invention provides a method of determining which positions in the protein will lead to stabilization when substituted.

Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term "about".

The native or wild-type protease from which the mutant proteases according to the invention are derived is a B. lentus alkaline protease (BLAP) obtained from B. lentus DSM 5483 having 269 amino acid residues, a molecular mass of 26,823 daltons, and a calculated isoelectric point of 9.7 based on standard pK values. The BLAP gene is obtained by isolating the chromosomal DNA from the B. lentus strain DSM 5483, constructing DNA probes having homology to putative DNA sequences encoding regions of the B. lentus protease, preparing genomic libraries from the isolated chromosomal DNA, and screening the libraries for the gene of interest by hybridization to the probes.

Mutant B. lentus DSM 5483 proteases have been made which are derived by the replacement of at least one amino acid residue of the mature form of the B. lentus DSM 5483 alkaline protease. The sites for replacement are selected from the group consisting of Ser3, Va14, Ser36, Asn42, Ala47, Thr56, Thr69, Glu87, Ala96, Ala101, Ile102, Ser104, Asnl14, Hisl18, Ala120, Ser130, Ser139, Thr141, Ser142, Ser157, Ala188, Val193, Val199, Gly205, Ala224, Lys229, Ser236, Asn237, Asn242, His243, Asn255, Thr268. The replacement amino acid residues are listed in Table 2. The numbering of the mutant proteases is based on the B. lentus DSM 5483 wild-type protease as given in the SEQ ID NO:52.

Genes which express the mutant B. lentus DSM 5483 proteases according to the invention are made by altering one or more codons of the wild-type B. lentus DSM 5483 alkaline protease gene which encode for a protease derived by accomplishing at least one of the amino acid substitutions listed in Table 2.

The protease sites listed in Table 2 are sites predicted to affect thermal and surfactant stability relative to the wild-type protease. These sites are identified by means of a computer based method which compares the three dimensional structure of the wild-type protease (henceforth, the target protein) and a homologous protease (henceforth, the reference protein). The three dimensional coordinates of the wild-type protease are probed with an uncharged probe molecule to produce a probe-accessible surface which has an external surface the interior of which contains one or more probe-accessible internal cavities. The amino acids of the reference protein having side chains lying outside the solvent-accessible surface or inside the internal cavities of the target protein are identified by aligning the three dimensional coordinates of the target protein and the reference protein.

Proteins having greater thermal and surfactant stability are produced by replacing the amino acid in the target protein if the amino acid in the target protein can be changed without creating unacceptable steric effects. The amino acid in the target protein is altered by site directed mutagenesis of the gene which expresses the target protein.

Genetic constructs are made which contain in the direction of transcription a promoter, ribosomal binding site, initiation codon and the major portion of the pre region of the Bacillus licheniformis ATCC 53926 alkaline protease gene operably linked to a portion of the pre region and all of the pro and mature regions of the Bacillus lentus DSM 5483 alkaline protease gene followed by a 164 bp DNA fragment containing the transcription terminator from the ATCC 53926 alkaline protease gene. The Bacillus lentus DSM 5483 alkaline protease gene is altered to produce a mutant gene which encodes for a protease derived by accomplishing at least one of the amino acid substitutions listed in Table 2. Mutant protease is made by fermenting a Bacillus strain transformed with a genetic construct containing a mutated Bacillus lentus DSM 5483 alkaline protease gene.

FIG. 1A through 1P collectively depict the atomic coordinates for Bacillus lentus alkaline protease (BLAP) to 1.4 .ANG. resolution.

FIG. 2 shows the restriction map for plasmid pCB13C which contains a hybrid gene fusion between the Bacillus licheniformis ATCC 53926 protease gene and the Bacillus lentus DSM 5483 BLAP gene. The promoter, ribosomal binding site and presequence (P-53926) from ATCC 53926 were fused to the pro- and mature sequence of the SLAP gene. The transcription terminator of ATCC 53926 (T-53926) was appended to the SLAP coding region.

FIG. 3 shows the restriction map for plasmid pMc13C which is derived from pMac5-8 and contains the SLAP gene and carries an amber mutation in the Ap.sup.R gene which renders it inactive.

One aspect of the invention relates to mutant proteolytic enzymes which have superior thermal stability and surfactant stability relative to the wild-type protease as determined by laboratory tests. The mutant proteases according to the invention are those derived by the replacement of at least one amino acid residue of the mature Bacillus lentus DSM 5483 alkaline protease wherein said one amino acid residue which is selected from the group consisting of Ser3, Va14, Ser36, Asn42, Ala47, Thr56, Thr69, Glu87, Ala96, Ala101, Ile102, Ser104, Asnl14, Hisl18, Ala120, Ser130, Ser139, Thr141, Ser142, Ser157, Ala188, Val193, Val199, Gly205, Ala224, Lys229, Ser236, Asn237, Asn242, His243, Asn255, Thr268 is replaced with the amino acid residues listed in Table 2. Table 2 shows the identity and position of the wild-type amino acid and the amino acid residue(s) which replace it in the mutant protein. For example, the first entry in Table 2 shows Ser3, a serine residue at position 3 which can be replaced by threonine (abbreviated as T using the one letter code for amino acids) or any small amino acid. A small amino acid is defined as glycine, alaninc, valine, serine, threonine or cysteine. A small hydrophobic amino acid is defined as glycine, alaninc, threonine, valine or isoleucine. A charged amino acid is defined as lysine, arginine, histidine, glutamate or aspartate. The abbreviation a.a. stands for "amino acid" residue.

The amino acid sequences of the preferred proteolytic enzymes are given in SEQ ID NO:1 to SEQ ID NO:51. The preferred mutated B. lentus DSM 5483 proteases which are encoded for by genes according to the invention as disclosed above are given in SEQ ID NO: 53 to 105. These proteases are produced by bacterial strains which have been transformed with plasmids containing a native or hybrid gene, mutated at one or more nucleotide base pairs by known mutagenesis methods. These mutant genes encode for proteases in which selected amino acid residues have been substituted for by other amino acids.

The mutant proteases according to the invention are listed in Table 3.

Any of the proteases listed in Table 3 will exhibit greater stability in some manner than the wild-type protease BLAP. The entries under the "Mutation" heading of Table 3 shows the identity of the wild-type amino acid (using the one letter code), its position, and the amino acid which replaces it in the mutant protease. For example, S3T signifies that the serine at position 3 of the mature protease is replaced with a threonine. Some of the preferred mutant proteases are single replacements at specific locations such as a protease wherein valine at position 4 is replaced by isoleucine to specific combinations of replacements such as a protease wherein threonine at position 141 is replaced by tryptophan and asparagine at position 237 is replaced by alanine. The latter protease containing two replacements is one of only a number of possibilities.

The preferred mutant proteases according to the invention are identified as: (S3T, V4I, A188P, V193M, V199I); E87R; (S3T, A188P, V193M, V199I); Nl14S; (V4I, A188P, V193M, V199I); A47W; (S139Y, A188P, V193M, V199I); A120S; (S130T, S139Y, A188P, V193M, V199I); T56V; A120V;(A188P, V193M, V199I); G205V; (S3T, A188P, V193M); S130A; S130T; S157T; A96I; (S104T, S139Y, A224V); S139A; S142T; S139T; I102W; V193M; A96N; N42F; S142A; Hl18F; N237A; N255P; (T141W, N237A); T268V; K229W; T141W; (A188P, V193M); V4I; S3T; S139Y; N242A; S236T; S36A; H243A; A101T; S236A; A188P; (S3T, V4I, A188P, V193M); V193M; S104T; T69V; (V4I, A188P, V193M); A224V; V199I. The system used to designate the above preferred proteases first lists the amino acid residue in the mature form of the B. lentus DSM 5483 alkaline protease at the numbered position followed by the replacement amino acid residue using the one letter codes for amino acids. For example, V193M is a protease in which valine has been replaced by methionine at position 193 of the mature B. lentus DSM 5483 alkaline protease. A mutant protease identified by more than one such designation is a mutant protease which contains all of the indicated substitutions. For example, (A188P, V193M) is a protease in which valine has been replaced by methionine at position 193 of the mature B. lentus DSM 5483 protease and alanine at position 188 has been replaced by proline.

Mutant forms of the B. lentus DSM 5483 alkaline protease are prepared by site-specific mutagenesis of DNA encoding the mature form of either wild-type BLAP, or a mutant BLAP. The DNA fragment encoding the mature form of wild type BLAP was prepared using plasmid pCB13C. Plasmid pCB13C contains a hybrid fusion between the B. licheniformis ATCC 53926 protease gene and the B. lentus DSM 5483 BLAP gene, shown in FIG. 2. Specifically, this hybrid fusion contains DNA encoding the promoter, ribosomal binding site, and 21 residues of the pre sequence from the ATCC 53926 protease gene fused to a DNA sequence encoding the last five residues of the BLAP pre sequence and all of the pro and mature residues of BLAP. This fusion is referred to as the ClaI fusion because this restriction 15 site is located at the juncture between the ATCC 53926 and DSM 5483 DNA's. A new ClaI restriction site had to be introduced into the ATCC 53926 alkaline protease gene near to the junction of the pre and pro sequences. The ClaI site was introduced into the ATCC 53926 alkaline protease gene by using a polymerase chain reaction (PCR) to amplify a DNA fragment containing sequence information from the N-terminal part of the ATCC 53926 alkaline protease gene. The amplified fragment included the ATCC 53926 alkaline protease promoter, ribosomal binding site, initiation codon, and most of the pre sequence. This 292 bp DNA fragment was flanked by AvaI and ClaI restriction sites at its 5' and 3' ends, respectively. The BLAP gene already contained a naturally occurring ClaI site at the corresponding position. Analysis of the DNA sequence across the fusion of the ATCC 53926 and BLAP genes confirmed the expected DNA and amino acid sequences.

Before any mutagenesis can be carried out, the gene is subcloned into the mutagenesis vector pMa5-8. This is accomplished by synthesizing a DNA fragment containing the ClaI fusion gene and the ATCC 53926 transcription terminator as a SalI cassette using the PCR. The PCR was carried out using conditions as described by the manufacturer (Perkin Elmer Cetus, Norwalk, CT.). In the PCR, two synthetic oligonucleotides bearing SalI sites are used as primers and Escherichia coli vector pCB13C DNA as a template. After cutting the PCR product with SalI, this fragment is cloned into the mutagenic plasmid pMc5-8 which has previously been cut with SalI and dephosphorylated with bacterial alkaline phosphatase. Plasmids pMc5-8, and pMa5-8 described below were obtained from H.-J. Fritz and are described by Stanssens, P., et al. (1989) Nucleic Acids Res. 17:4441-4454. SalI sites are chosen to allow the PCR fragment to be cloned into pMc5-8 in both orientations. The ligation mix is transformed into E. coli WK6. Chloramphenicol resistant (Cm.sup.R) transformants are screened for the presence of an insert and a correct plasmid construct pMc13C is identified as shown in FIG. 3. Once the gene is cloned into the pMc vector and desirable sites for mutation are identified, the mutation(s) is introduced using synthetic DNA oligonucleotides according to a modification of a published protocol (Stanssens, P., et al. (1989) Nucleic Acids Res. 17:4441-4454). The oligonucleotide containing the mutation(s) to be introduced is annealed to a gapped duplex (gd) structure which carries the BLAP gene on a segment of single stranded (ss) DNA. The gapped duplex can be formed by annealing linear ss DNA from pMc13C with denatured and restricted pMa5-8 DNA. Plasmid pMa5-8 contains an active ampicillin resistance gene but has an inactivating point mutation in the chloramphenicol resistance gene, whereas plasmid pMc13C contains, in addition to an intact BLAP gene, an active chloramphenicol resistance gene, but has an inactivating point mutation in the ampicillin resistance gene. The annealed product is the gd DNA which is a double stranded heteroduplex with ass DNA gap spanning the entire cloned BLAP gene. The mutant oligonucleotide is able to anneal to homologous ss BLAP DNA within the gap and the remaining gap is filled in by DNA polymerase I (Klenow fragment) and ligated using T4 DNA ligase, purchased from New England Biolabs Inc., Beverly, Ma. The mutagenic efficiency of such a system can be improved by the use of Exonuclease III (Exo III) purchased from New England Biolabs Inc., Beverly, MA. Exo III is an exodeoxyribonuclease that digests double stranded DNA from the 3' end. As a free 3' end is required, closed circular ss DNA or ds DNA is unaffected by this enzyme. A subsequent treatment of the product of the fill-in reaction with Exo III removes any species with only partially filled gaps. This significantly improves the mutagenic efficiency and is the preferred mutagenesis method. The product of the fill-in reaction is then transformed into a repair deficient E. coli strain such as WK6mutS and ampicillin resistant transformants (Ap.sup.R) are selected. Replication of the transformed heteroduplex phasmid results in two different progenies. One progeny contains the wild type BLAP gene and the intact chloramphenicol resistance gene, but an inactive ampicillin resistance gene. The other progeny contains a BLAP gene carrying the mutation of interest and is resistant to ampicillin but not to chloramphenicol.

Selection of Ap.sup.R, Cm.sup.s mutant transformants with ampicillin is not sufficient to stop some background growth of the Ap.sup.s, Cm.sup.R progeny carrying the wild type BLAP gene. Therefore, it is necessary to perform a second transformation into E. coli using plasmid DNA prepared from the Ap.sup.R transformants of the WK6mutS strain. This second transformation uses a low plasmid concentration with a large number of recipient cells of a suppressor deficient strain of E. coli such as WK6. This approach decreases the likelihood of a recipient cell receiving plasmid DNA from both progeny. Ap.sup.R transformants are selected and plasmid DNA from several transformants is isolated and screened for the presence of the mutation. The pMa mutant derivative of the first mutagenesis round can be used for a second round of mutagenesis by preparing ss DNA of that species and annealing it to XbaI/HindIII restricted and denatured DNA of pMc5-8. Plasmid pMc5-8 is identical to pMa5-8 except that it contains an active chloramphenicol resistance gene and an inactive ampicillin resistance gene. The general procedure is the same as that described above.

The mutant BLAP proteases can be produced by transferring the mutant BLAP genes from their particular E. coli pMa13C derivative vector into a plasmid vector which can replicate in Bacillus. To accomplish this, the mutant BLAP genes are separated from their pMa13C plasmids by digestion with the restriction endonucleases AvaI and SstI, followed by ligation to the larger AvaI/SstI fragment from either plasmid pH70 or pC51. These AvaI/SstI fragments from pH70 and pC51 include the DNA sequences necessary for replication in Bacillus and encode either kanamycin resistance (Km.sup.R) or tetracycline resistance (TC.sup.R), respectively. Plasmid pH70 is constructed by cloning the ATCC 53926 alkaline protease gene carried on a EcoRI/BamHI DNA fragment into the Km.sup.R plasmid pUBl10 between the EcoRI and BamHI sites. Plasmid pC51 is constructed by cloning the ATCC 53926 protease gene carried on a EcoRI-BamHI fragment into the Tc.sup.R plasmid pBC16 between the EcoRI and BamHI sites. The larger AvaI-SstI fragment from either pH70 or pC51 used for cloning the mutant BLAP genes is first purified from other DNA fragments by high pressure liquid chromatography (HPLC) on a Gen-Pak FAX column (Waters, Milford, MA). The column is 4.6 mm by 100 mm in size and contains a polymer-based high performance anion-exchange resin. Conditions for elution of the DNA are a flow rate of 0.75 ml/min with a gradient of Buffer A (25 mMtris(hydroxymethyl)aminomethane (Tris) pH 8.0 containing 1 mMdisodium ethylenediamine tetraacetic acid (EDTA)) and Buffer B (25 mM Tris pH 8.0, 1 mM EDTA, 1 M NaC1) starting at 50% each and reaching a final concentration of 30% Buffer A and 70% Buffer B.

After ligation the mutant BLAP plasmids are transformed into B. subtilis DB104. The genes encoding the major alkaline and neutral proteases present in this strain have been inactivated (Kawamura, F., and Doi, R.A. (1984) J. Bacteriol. 160:442-444). Cells of B. subtilis DB104 transformed by these plasmids grow on a nutrient-skim milk agar in the presence of either kanamycin or tetracycline. Transformants of DB104 that manufacture mutant protease are identified by the formation of clear zones of hydrolysis in the skim milk. Confirmation that the protease-producing transformants carry a plasmid-borne BLAP gene with the desired mutation(s) is accomplished by purifying plasmid DNA from a culture of each transformant. The plasmid DNA is purified away from cell protein and chromosomal DNA by SDS-salt precipitation followed by chromatography over a Qiagen ion-exchange column (Qiagen corporation, Studio City, CA). AvaI-SstI digested plasmid DNAs from different transformants are compared with AvaI/SstI-digested derivatives of plasmid pH70 or pC51 known to carry an intact BLAP gene. Restriction digests of these plasmids are compared by agarose gel electrophoresis to identify plasmids that have the proper-sized AvaI/SstI DNA fragments. Selected plasmid DNAs are then sequenced across the region of the expected BLAP mutation(s) to confirm that the desired mutation(s) are present. One or more clones of each BLAP mutation are stored frozen in 15% glycerol at -70.degree. C. and also cultivated in shake flasks (Example 4, Production of Proteases) to produce mutant protease for characterization.

Another aspect of the invention provides a computer based method for identifying the sites which affect the storage, thermal, SDS and pH stability of a protein. This method is based on the hypothesis that protein stability may be enhanced by decreasing the volume of internal cavities and improving surface packing of amino acid side chains. The interior of a protein contains many apolar amino acids which are tightly packed into a nearly crystalline state. One way in which these interior amino acids affect protein stability is through packing effects. These include van der Waal interactions, distortion of the remainder of the protein and electrostatic effects. Packing effects have been studied by measuring the contribution of methyl groups in the interior of a protein to the overall stability of the protein. It has been estimated that the removal of a methyl group from the interior of a protein destabilizes it by about 1.1 kcal/mol assuming no other perturbations occur (Kellis, J.T., Jr., et al. (1988) Nature 333:784-786). However, the inverse may not be true. Simply adding buried hydrophobic groups may not increase protein stability because the total effect of adding or deleting a methyl group on the local packing structure must be considered. As the protein interior has a para-crystalline structure (Chothia, C. (1975) Nature 254:304-308), small distortions in the remainder of the structure resulting from the addition methyl group may exact a high cost and reduce rather than increase stability.

While it is known in the art to make certain substitutions which may affect protein stability, there is no known way of identifying which sites in the protein will lead to stabilization when substituted. For example, it has been suggested that protein stability would be increased if alanine were substituted for glycine or serine; or if threonine were substituted for serine (Matthews, B.W., et al. (1987) Proc. Natl. Acad. Sci. 84:6663-6667); or if proline were substituted for glycine. However, the sites in which one or more of these substitutions should be made has been so far unpredictable. Other methods depend on comparisons of the amino acid sequences of different but related proteins. However, this does not show which sites are important to stability, only which positions are different.

There are two computer based methods for identifying the sites which affect the stability of a protein according to the invention.

In the first method for identifying sites which affect the stability of protein, the first step comprises generating a probe-accessible surface by analyzing the target protein coordinates with an uncharged probe molecule having a radius of about 0.9 to about 2.0 .ANG.. It is important that no water molecules be included in the protein structure during this analysis. The second step of this method is the identification of the amino acids which form the boundaries of the internal cavities. These amino acids comprise a set of positions which, if mutated, may increase the stability of the protein. An increase in stability can be achieved by amino acid substitutions which decrease the volume of the internal cavities.

The molecular modeling program QUANTA (trademark of Polygen Corporation, 200 Fifth Ave., Waltham, MA02254) was used to calculate probe-accessible surfaces as well as perform the alignment of the three dimensional coordinates of the proteins. These functions can be carried out equally well by other molecular modeling programs which are also commercially available. The following is a list of commercially available programs which can also be used to calculate probe-accessible surfaces: Insight or InsightII (trademark of Biosym Technologies, Inc., 10065 Barnes Canyon Road--Suite A, San Diego, Calif. 92121), BIOGRAF (trademark of Biodesign, Inc., 199 S. Los Robles Ave., #270, Pasadena, Calif. 91101) or Sybyl (trademark of Tripos Associates, 1699 S. Hanley Road, St. Louis, MO 63144)

The probe-accessible surface referred to in step 1 of the first method can be generated in several ways (Richards, F.M. (1977) Annu. Rev. Biophys. Bioeng. 6:151-176): A spherical probe of radius R (0.9 to 2.0 .ANG.) is allowed to roll on the outside of a molecule while maintaining contact with the van der Waal surface. The surface defined by the center of the probe is defined as the probe-accessible surface. Alternatively, a similar surface can be generated by increasing the van der Waal radii of all the atoms in a protein by the radius of the probe. Overlapping surfaces are eliminated and the remaining surface represents the probe-accessible surface. In the preferred embodiment, a three-dimensional box of dimensions 50.times.50.times.50 .ANG. with a 1 .ANG. grid size in all three dimensions (x, y, and z) is centered on the center of mass of the target protein coordinates. Most preferrably, the dimensions of the probe map are adjusted such that all of the protein atoms fall within the probe map's bounds. The grid size of 1 .ANG. provides a sufficiently high resolution to clearly define the probe-accessible surface although another grid size could be used, ranging from 0.5 to 3.0 .ANG.. An uncharged probe molecule is positioned at each grid point and the energy of interaction between the probe and the target protein atoms is determined. The energy of nonbonded interaction (E.sub.nb) contains only the van der Waal component such that ##EQU1## where r is the nonbonded distance, .epsilon..sub.ij is the dispersion well depth and .sigma..sub.ij is the Lennard-Jones diameter. The result is a map consisting of a box with energy values at each grid point. This map can be contoured at a particular energy value to generate surfaces which correspond to the solvent accessible surface and internal cavities (Goodford, P.J. (1985) J. Med. Chem. 28:849-857). The value at which to contour the maps can vary depending on the particular radius used and the parameters used to define the probe molecule and the particular method used to generate the probe. The preferred embodiment is to used a probe radius of 0.9 .ANG. and contour the surface at 10 kcal/mol.

The external surface of the probe-accessible surface is also known as the solvent-accessible surface. Probe-accessible surfaces inside of the solvent accessible surface are defined as internal cavities and represent cavities large enough to accommodate a molecule with a radius equal to the probe radius. The presence of such a cavity on the inside of a protein does not imply that the cavity will in fact be filled by one or more solvent molecules.

The second step of the method for identifying sites which affect the stability of a protein is the identification of the amino acids which form the internal cavities. The internal cavities are defined by the amino acids which make up its boundaries. These amino acids comprise a set of positions which, if mutated, may increase the stability of the protein.

In a second method for identifying sites which affect the stability of a protein , the first step comprises generating a probe-accessible surface by analyzing the target protein coordinates with an uncharged probe molecule having a radius of about 0.9 to about 2.0 .ANG.. It is important that no water molecules be included in the protein structure during this analysis. This step is the same as the first step of the method set forth above.

The second step involves aligning the three dimensional structure of the target protein and a reference protein by moving the three dimensional coordinates of the reference protein into the coordinate frame of the target protein. The reference protein is usually chosen so that a high degree of similarity exists between it and the target protein so that packing differences between the target and reference protein which potentially affect the stability of the target protein can be identified. The reference protein can be any protein for which a three dimensional structure is available which is homologous to the target protein. Examples of such proteins include but are not limited to subtilisin Carlsberg, subtilisin BPN', proteinase K, and Thermitase. When the target protein is BLAP, one preferred reference protein is Thermitase. Thermitase is an extra-cellular subtilisin-like serine protease isolated from Thermoactinomyces vulgaris (Fr o/ mmel, C., et al. (1978) Acta Biol. Med. Ger. 37:1193-1204). The protein amino acid sequence of thermitase is 42% identical to BLAP. The high degree of similarity between these two proteins provides an ideal system with which to examine packing differences that affect BLAP stability. In this second step the three 5 dimensional structures of Thermitase and BLAP are aligned using the computer program QUANTA.TM.. The three dimensional alignment is carried out by first aligning the primary sequences of the two proteins to determine which amino acids are equivalent. This is accomplished using FASTA (Myers, E.W., and Miller, W. (1988) Comput. Applic. Biosci. 4:11-17; Pearson, W.R., and Lipman, D.J. (1988) Proc. Natl. Acad. Sci. USA 85:2444-2448). Based on this alignment of the primary sequence, residues are matched for subsequent alignment of the three dimensional structures using MULTLSQ (Sutcliffe, M.J., et al. (1987) Protein Eng. 1:377-384; Kabsch, W. (1976) Acta Cryst. A32:922-923). This program uses one structure as fixed coordinates (the target protein coordinates) and then rotates and translates a second structure (the reference protein coordinates) so as to give the smallest root mean squared (r.m.s.) deviation between the two sets of three dimensional coordinates. For example, the alignment of the BLAP and thermitase three dimensional coordinates results in an r.m.s. deviation between equivalent .alpha.-carbons of 0.8 .ANG.. This demonstrates that the amino acid sequences of BLAP and thermitase fold into three dimensional structures which are extremely similar.

In the third step, the alignment of the three dimensional structures is used to identify sites which affect the stability of the target protein. This can be accomplished by a variety of methods. Using a computer program designed to display protein structures and surfaces such as QUANTA.TM., the structure of the reference protein can be displayed with the probe-accessible surface. The combined display of the reference protein and probe-accessible surface can then be visually examined to determine which amino acids in the reference protein fall outside of the solvent-accessible surface or inside internal cavities. An alternative method which can be used comprises coloring the atoms of the reference protein by determining whether amino acids in the reference protein fall outside of the solvent-accessible surface or inside internal cavities. The probe-accessible surface map (probe map) was used to color the atoms in the transformed subtilisin BPN' structure. In order to color each atom, an energy value needs to be interpolated from the probe map at each atomic coordinate.

The probe map consists of three dimensional grid with an energy value (E) at each grid point. In the preferred embodiment, the probe map is a 50.times.50.times.50 .ANG. box centered on the center of mass of the protein with a 1 .ANG. grid unit in all three dimensions (x, y, and z). In its optimal conception, the size of the probe map is adjusted such that all of the protein atoms fall within the probe map's bounds. The energy value at each protein atom position was approximated by interpolating from the energy values from the surrounded eight grid points in the probe map. Given the energy value at each point from the probe map, the grid spacing, and the atomic coordinate, it is a simple matter for any one skilled in the art to interpolate an energy value at each atomic coordinate.

In one such method, an energy value of zero is assigned arbitrarily if an atom falls outside the bounds of the map. From a given atomic coordinate (x,y,z), the eight closest grid points from the probe map which surround (x,y,z) are identified such that (x.sub.1 <x<x.sub.2), (y.sub.1 <y<y.sub.2), and (z.sub.1 <z<z.sub.2). The eight grid points are then A (x.sub.1, y.sub.1, z.sub.1), B (x.sub.1, y.sub.1, z.sub.2), C (x.sub.1, y.sub.2, z.sub.2), D (x.sub.1, Y.sub.2, z.sub.1) , E (x.sub.2, y.sub.1, z.sub.1) , F (x.sub.2, y.sub.1, z.sub.2) , G (x.sub.2, y.sub.2, z.sub.2), and H (x.sub.2, y.sub.2, z.sub.1). The energy value (E) at a given grid point such as (x.sub.1, y.sub.1, z.sub.1) is then E (x.sub.1, y.sub.1, z.sub.1) or equivalently E.sub.A. The energy at a specific atomic coordinate E (x,y,z) can be interpolated from the probe map given the eight nearest surrounding grid points (A through H, as described above) and the value at each grid point (E.sub.A through E.sub.H). The equation which was used for calculating the energy at specific atomic coordinates, E (x,y,z), is shown in Equation (2). The energy value at each coordinate can then be stored and used to display the molecule. ##EQU2##

The protein atoms were colored on the basis of this interpolated energy value. The protein was displayed using QUANTA.TM. and atoms with interpolated energies below 10 kcal/mol were colored as red. Atoms with interpolated energies above 10 kcal/mol were colored green. Visual inspection allowed identification of side chains which penetrated the solvent accessible surface or penetrated internal cavities.

There are also two computer based methods for increasing the stability of a protein. The first method comprises the steps of: (1) generating a probe-accessible surface of said target protein by probing the coordinates of said protein with an uncharged probe molecule having a radius of about 0.9 to about 2.0 .ANG., wherein said probe-accessible surface has an external surface the interior of which contains one or more probe-accessible internal cavities; (2) identifying the amino acids which make up the boundaries of the internal cavities, wherein said amino acids comprise a set of sites which when mutated increase the stability of the protein; (3) identifying an amino acid mutation which would decrease the volume of said internal cavities; (4) determining if said amino acid in said target protein can be changed without creating unacceptable steric interactions; (5) replacing the amino acid in said target protein by site-directed mutagenesis of the gene which expresses said target protein.

The first two steps of the above first method for improving the stability of a protein are the same as those disclosed above for the first computer based method for identifying the sites which affect the stability of a protein.

In step (3) an amino acid identified in step (2) is examined with the goal of identifying a mutation which would decrease the volume of said internal cavity. The size, shape and position of said internal cavity often defines and limits what mutations are acceptable and allowable given the distinct shape and size of each individual amino acid side chain. However, as a particular site in the protein has been identified for mutation, appropriate mutations can be also be determined by applying any of the various heuristics which define generally acceptable mutations (Matthews, B.W., et al. (1987) Proc. Natl. Acad. Sci. 84:6663-6667; Menendez-Arias, L., and Argos, P. (1990) J. Mol. Biol. 206:397-406; Sandberg, W.S., and Terwilliger, T.C. (1991) Trends Biotechnol. 9:59-63; Bordo, D., and Argos, P. (1991) J. Mol. Biol. 217:721-729).

In step (4) a determination is then made if the amino acid identified for change in the target protein can be mutated or changed without creating a conformation of the target protein having unacceptable steric interactions. The separation distance between two atoms considered unacceptably short is some percentage of the sum of the van der Waal radii of the two atoms in question. Values of 90-95% of the sum of the van der Waal radii are common though others could be used. Common atoms between the original and replacement amino acid side chain are located and fixed in the same position. The new amino acid is rotated to find the position with the least number of close contacts or unacceptable steric interactions (distances shorter than physically reasonable). The separation distance at which two atoms are considered unreasonably short is some percentage of the sum of the van der Waal radii of the two atoms in question. Values of 90-95% of the sum of the van der Waal radii are common though others could be used. If all conformations of the new amino acid have close contacts, the amino acid substitution is rejected. A conformation with no close contacts which can be matched to a preferred amino acid conformation as defined by Ponder, J.W., and Richards, F.M. (1987) J. Mol. Biol. 193:775-791, is most highly desirable. In step (6) the amino acid identified for change to the corresponding amino acid in the same position in the reference protein is changed by site-directed mutagenesis of the gene which expresses the target protein by the methods disclosed above.

The second method comprises the steps of: (1) generating a probe-accessible surface of said target protein by probing the three dimensional coordinates of said protein with an uncharged probe molecule having a radius of about 0.9 to about 2.0 .ANG., wherein said probe-accessible surface has an external surface the interior of which contains one or more probe-accessible internal cavities; (2) aligning said three dimensional coordinates of said target protein and a reference protein by moving the three dimensional coordinates of said reference protein into the coordinate frame of said target protein; (3) identifying an amino acid in said reference protein whose side chain lies outside said solvent-accessible surface of said protein or inside said internal cavities of said target protein; (4) identifying the amino acid in said target protein which occupies the equivalent position as said amino acid in said reference protein; (5) determining if said amino acid in said target protein can be changed without creating unacceptable steric effects; (6) replacing the amino acid in said target protein with the corresponding amino acid in the equivalent position in said reference protein by site-directed mutagenesis of the gene which expresses said target protein.

The first three steps of this method are the same as steps (1), (2), and (3) of the second method for the second computer based method for identifying the sites which affect the stability of a protein.

In step (4) the amino acid in the target protein which occupies the equivalent position as the amino acid in the reference protein is identified. Equivalency is determined from the primary sequence alignment and three dimensional structure alignment described above. Given two protein structures, a target and a reference structure, which have been aligned, equivalent amino acids are defined as pairs of amino acids, one from the target and one from the reference protein, which may differ in identity but occupy close to the same position in the secondary and tertiary structure of the two proteins.

The following examples are meant to illustrate but not to limit the invention.

The structure of BLAP was obtained by X-ray crystallography and solved to 1.4 .ANG.. The atomic coordinates are shown in FIG. 1. Water molecules were removed from the structure and the protein coordinates were used to generate a probe-accessible surface using a computer program QUANTA.TM. (version 3.0). This program can be used to calculate a probe-interaction map. The coordinates of BLAP were read into the computer and the following parameters were set in order to perform the probe interaction grid calculation. A Van der Waal calculation was requested with a "proton" probe (radius of 0.9 .ANG.) with a charge of 0.0. The box dimensions were set to 50 .ANG. with a grid size of 1 .ANG. centered on the e-carbon of residue 219. The maximum energy was set to 500 and the minimum to -100. This means that energy values which exceed 500 will be set to 500. An energy value will exceed 500 when the probe is very close to an atom in the protein. The calculations were performed on a Silicon Graphics Inc. (2105 Landings Drive, Suite 2105, Mountain View, Calif. 94043) 4D/220 PowerIris.TM. workstation. QUANTA.TM. was used to visualize the probe-accessible surface. The map was contoured at 50 kcal/mol but this value depends on the particular constants in use and the method used to generate the probe accessible surface. The map was displayed simultaneously with the structure of BLAP and amino acid side chains which defined the boundaries of the internal cavities were identified visually.

One such amino acid was threonine-69. This side chain is completely buried with only 2% of its surface being solvent accessible. The hydroxyl group of the side chain defined part of the border of two internal cavities. These particular cavities are occupied by water molecules 278 on one side, and 280 on the other. Mutating this amino acid to valine represents a conservative change which increases the hydrophobicity of the side chain while having little effect on size and shape. Using computer modeling, it was determined that mutating threonine-69 to valine would not create any close contacts with other protein atoms or significantly perturb the structure if the valine occupies the same position as the hydroxyl of threonine-69 in the wild type protein. An oligonucleotide was synthesized which carried a mutation of the codon for threonine-69 to valine (T69V). This oligonucleotide was used to create a site directed mutation in the BLAP gene which was subcloned into a Bacillus vector and expressed in B. subtilis DB104 (See Examples 4 and 5). Strains were identified which were expressing the mutant protease and several shake flasks were prepared to produce the mutant protein (See Example 5). The mutant protease was purified from the shake flask media and characterized for surfactant and temperature stability (See Examples 7, 10, and 11).

The mutation T69V resulted in a 340% increase in the half-life of the protease at 50.degree. C., from 12 minutes to 41 minutes (See Table 3).

The three dimensional coordinates of subtilisin Carlsberg (lCSE) were obtained from the Brookhaven Protein Database (Bernstein, F.C., et al. (1977) J. Mol. Biol. 112:535-542). The protease structures were aligned using the molecular modeling program QUANTA.TM.. The BLAP coordinates were held fixed. The .alpha.-carbons of residues 1 to 32 of BLAP were matched to residues 1 to 32 of 1CSE, respectively; residues 40 to 60 of BLAP to residues 41 to 61 of 1CSE; residues 80 to 155 of BLAP to residues 82 to 157 of 1CSE; residues 170 to 269 of BLAP to residues 176 to 275 of lCSE. The BLAP structure was held fixed, and the 1CSE structure was rotated and translated such that the r.m.s. deviation between the .alpha.-carbons of matched residues was minimized. The translation vector (-10.68738, 31.28904, -5.32134) and the rotation matrix

were applied to the coordinates of 1CSE and the transformed coordinates were saved (henceforth, the transformed 1CSE structure). The final r.m.s. deviation between the matched 229 .alpha.-carbon pairs was 0.872 .ANG..

The probe-accessible surface map calculated in Example 1 was used to color the atoms in the transformed 1CSE structure. The entire map, which consists of three dimensional grid of (x, y, z) coordinates in space and an energy value at each position, was read into computer memory along with the protein coordinates (the transformed 1CSE structure). The energy value at each atom position was approximated by interpolating from the energy values of the surrounding eight nearest grid points in the probe map. The protein atoms were colored on the basis of this interpolated energy value. The protein was displayed using QUANTA.TM. and atoms were displayed in different colors depending on their interpolated energy value. For example, if the energy were greater than 400 the atoms were dark blue; between 300 and 400, light blue; 200 and 300, green; 200 to 100 yellow; and between -100 and 100, red. Visual inspection of such a display allowed identification of side chains which penetrated the solvent accessible surface or internal cavities.

One such amino acid was methionine-199 (1CSE numbering) in subtilisin Carlsberg. The amino acid was identified by visual inspection of the transformed 1CSE structure (as described above). Below, the coordinates of residue 199 from the transformed 1CSE structure are shown in the Brookhaven Protein Data Bank file format along with the interpolated energy values.

Column 1 is the record type; column 2 is the atom number; column 3 is the atom name; column 4 is the residue name; column 5 is the residue number; columns 6, 7 & 8 are the x, y, z coordinates of the atom, respectively; column 9 is the occupancy; column 10 is normally the temperature factor but this has been replaced with the interpolated energy value. Note that a value of 500 in this column means that the atom in nearly completely within the van der Waal surface of the BLAP molecule. When the probe map was calculated (see Example 1), energy values greater than 500 were set to 500. As can be seen, atoms 1370 and 1371 have significantly lower energy values (column 10). The end of this methionine residue extends into an internal cavity in the BLAP molecule.

This residue is equivalent in secondary and tertiary structure to valine-193 in BLAP. Using computer modeling, valine-193 in BLAP was changed to methionine. The .chi. values for the new methionine side chain in BLAP were taken from the subtilisin BPN' structure. In this conformation, the new side chain had no close contacts except for the .epsilon.-carbon of the methionine which contacted a crystallographic water in the BLAP structure.

An oligonucleotide was synthesized which mutated the codon for valine-193 to methionine (V193M) in the BLAP gene. This oligonucleotide was used to create a site directed mutation in the BLAP gene which was subcloned into a Bacillus vector and expressed in B. subtilis DB104 (See Examples 3, 4, and 5). Strains were identified which were expressing the mutant protease and several shake flasks were prepared to produce the mutant protein (See Example 5). The mutant protease was purified from the shake flask media and characterized for temperature and surfactant stability (See Examples 6, 7, 10, and 11).

The mutation V193M resulted in a 350% increase in the half-life of the protease at 50.degree. C. from 12 minutes to 42 minutes (See Table 3).

The three-dimensional coordinates of thermitase (1TEC) were obtained from the Brookhaven Protein Database (Bernstein, F.C., et al. (1977) J. Mol. Biol. 112:535-542). The structures of BLAP and 1TEC were aligned using the molecular modeling program QUANTA.TM. by matching equivalent .alpha.-carbons as listed below.

The BLAP structure was held fixed and the 1TEC structure was rotated and translated such that the r.m.s. deviation between the .alpha.-carbons of matched residues was minimized. The translation vector (14.92521, 33.43270, 40.92134) and the rotation matrix

were applied to the coordinates of 1TEC and the transformed coordinates were saved (henceforth, the transformed 1TEC structure). The final r.m.s. deviation between the matched 236 .alpha.-carbon pairs was 1.384 .ANG..

The probe-accessible surface map was used to color the atoms in the transformed 1TEC structure. The entire probe map was read into computer memory along with the coordinates of the transformed 1TEC structure. The energy value at each atomic position was interpolated from the energy values of the eight surrounding grid points in the probe map. The protein was displayed using QUANTA.TM. and atoms were displayed in different colors as a function of their interpolated energy value. For example, if the energy were greater than 400 the atoms were dark blue; between 300 and 400, light blue; 200 and 300, green; 200 to 100 yellow; and between -100 and 100, red. Visual inspection of such a display allowed identification of side chains which penetrated the solvent accessible surface or internal cavities.

One such amino acid was tyrosine-149 (1TEC numbering) in thermitase. The amino acid was identified by visual inspection of the transformed 1TEC structure. Below, the coordinates of residue 149 from the transformed 1TEC structure are shown in the Brookhaven Protein Data Bank file format along with the interpolated energy values.

Column 10 is normally the temperature factor but this has been replaced with the interpolated energy value. As can be seen, the phenyl ring of the tyrosine side chain has significantly lower energy values (column 10 of atoms CG, CD1, CD2, CE1, CE2 and CZ).

This residue is equivalent in secondary and tertiary structure to serine-139 in BLAP. Using computer modeling, serine-139 in BLAP was changed to tyrosine. The .chi. values for the new tyrosine side chain in BLAP were taken from the thermitase structure. In this conformation, the new side chain had no close contacts that could not be alleviated by small changes (less than 5.degree.) of the .chi. values. The modeled tyrosine side chain in BLAP fits neatly into a crevice on the surface of the BLAP protein between two surface helices.

An oligonucleotide was synthesized which mutated the codon for serine-139 to tyrosine (S139Y) in the BLAP gene. This oligonucleotide was used to create a site directed mutation in the BLAP gene which was subcloned into a Bacillus vector and expressed in B. subtilis DB104 (See Examples 3, 4, and 5). Strains were identified which expressed the mutant protease and several shake flasks were prepared to produce the mutant protein (See Example 5). The mutant protease was purified from the shake flask culture and characterized for temperature and surfactant stability (See Examples 6, 7, 10, and 11).

The mutation S139Y resulted in a 216% increase in the half-life of the protease at 50.degree. C., from 12 minutes to 26 minutes (See Table 3).

This mutagenesis procedure was first described by Stanssens, P., et al. (1989) Nucleic Acids Res. 17:4441-4454. While this is the preferred method, many other methods could be used to introduce oligonucleotide site-directed mutations, particularly those which use single stranded DNA. For example, the method of Kunkel (Kunkel, T.A. (1985) Proc. Natl. Acad. Sci. USA 82:488-492) has also been used.

A synthetic oligonucleotide was synthesized which mutates the codon of threonine-69 to the codon for valine. The mutagenic oligonucleotide was annealed to a gapped duplex DNA which carries the BLAP gene on a segment of single stranded (ss) DNA. The gapped duplex (gd) was formed by denaturing linear DNA's from pMc13C and pMa5-8 followed by re-annealing. The mutagenic oligonucleotide annealed to homologous ss BLAP DNA within the gap and the remaining gap was filled in by a DNA polymerase and ligated using T4 DNA ligase. Subsequent treatment of the product of the fill-in reaction with ExoIII removed any species with only partially filled gaps.

The product of the fill-in reaction was then transformed into a repair deficient E. coli strain such as WK6mutS. Plasmid DNA from the recombinant E. coli WK6mutS was prepared and transformed in a low plasmid/recipient ratio into a suppressor deficient strain of E. coli such as WK6. Ampicillin resistant transformants were selected and plasmid DNA of several candidates was purified and checked for the presence of the mutation.

The mutant BLAP protease was expressed by transferring the mutant BLAP genes from their particular E. coli pMa13C derivative vector into a plasmid vector which can replicate in Bacillus such as pH70 or pC51. In the following example, the plasmids pC51 and pH70 can be used interchangeably with the exception that plasmid pH70 encodes resistance to kanamycin while plasmid pC51 encodes resistance to tetracycline. The mutant BLAP gene was separated from the pMa13C plasmids by digestion with the restriction endonucleases AvaI and SstI and then ligated with an AvaI-SstI cut fragment of plasmid pH70 that includes the regions necessary for kanamycin resistance and for replication in Bacillus. The pH70 AvaI-SstI fragment was purified by high pressure liquid chromatography (HPLC). After ligation the mutant BLAP plasmids were transformed into B. subtilis DB104, a strain that has been engineered to inactivate its own genes encoding the major alkaline and neutral proteases. B. subtilis DB104 transformed by these plasmids were grown on a nutrient-skim milk agar in the presence of the antibiotic kanamycin. Clones that manufactured mutant protease were identified by the formation of clear zones of hydrolysis in the skim milk. Plasmid DNA was purified from these clones to verify that the protease-producing clones carried the a plasmid-borne BLAP gene with the desired mutation. The plasmid DNA was purified away from cell protein and chromosomal DNA by SDS-salt precipitation followed by chromatography over a Qiagen ion-exchange column (Qiagen Corporation). AvaI-SstI digested plasmid DNAs from different clones were compared with AvaI/SstI-digested derivatives of plasmid pH70 known to carry an intact BLAP gene. Plasmid digests were compared by agarose gel electrophoresis to identify plasmids that have the proper-sized AvaI/SstI DNA fragments. Selected plasmid DNAs were then sequenced across the region of the particular BLAP mutation to confirm that the mutation was present. One or more clones of each BLAP mutation were stored frozen in 15% glycerol at -70.degree. C. and also cultivated in shake flasks (Examples 4 and 5) to manufacture mutant protease for characterization.

Each strain of B. subtilis DB104 that carried a plasmid with one of the mutant BLAP genes was cultivated in shake flasks to make the mutant protease. Strains were grown in 50 ml precultures of (Difco) Luria Broth (LB) with the antibiotic kanamycin for pH70 derived clones or tetracycline for pC51 derived clones at 37.degree. C. and 280 rpm in a New Brunswick Series 25 Incubator Shaker. After 7 to 8 hours of incubation 2.5 or 5.0 ml of the preculture was transferred to 50 or 100 ml of MLBSP medium (Table 5), respectively, with either 20 .mu.g/ml of kanamycin, or 15 .mu.g/ml of tetracycline in 500 ml (Bellco) baffled shake flasks for growth and eventual production of the protease. These main shake flask cultures were incubated at 240 rpm and 37.degree. C. for 64 hours before the culture broths were treated to remove intact cells and cellular debris, and to reduce the pH to 5.8 before they were concentrated. The protease production of each culture was monitored by electrophoresis of culture supernatants with reverse polarity on 12.5% homogenous polyacrylamide gels with the Pharmacia PhastSystem.

A hot loop was used to streak each mutant strain from a frozen cryovial culture onto an LB-skim milk agar containing either 20 .mu.g/ml of kanamycin or 15 .mu.g/ml of tetracycline. The plates were incubated at 37.degree. C. for 20 to 24 hours. A single, isolated colony producing a good zone of hydrolysis of the skim milk was picked into a 250 ml Erlenmeyer flask containing about 50 ml Luria Broth (LB) which contained either 20 .mu.g/ml kanamycin or 15 .mu.g/ml of tetracycline. The broth was incubated in a New Brunswick Series 25 Incubator Shaker at 37.degree. C. with shaking at 280 rpm for 7 to 8 hours. Either 2.5 ml of the turbid preculture was transferred into 50 ml of MLBSP containing either 20 .mu.g/ml kanamycin or 15 .mu.g/ml of tetracycline in each of four baffled 500 ml flasks, or 5 ml of preculture was used as an inoculum for 100 ml of MLBSP broth with antibiotic contained in each of two 500 ml baffled flasks (a 5% v/v transfer). All flasks were incubated at 240 rpm and 37.degree. C. for 64 hours. After 64 hours of incubation the set of flasks for each culture was consolidated, transferred to 50 ml centrifuge tubes, and centrifuged at 20,000 g.sub.av for 15 minutes at 4.degree. C. The broth was filtered through Miracloth (Calbiochem Corp. #475855) into 400 ml beakers chilled on ice. The broth was slowly stirred on ice for 30 minutes before the broth pH was reduced to 5.8 by the slow addition of glacial acetic acid. More fine debris were removed by centrifugation again at 20,000 g.sub.av and the broth was filtered through Miracloth into graduated cylinders to measure the volume. Two sets of 1 ml samples were made for PhastSystem gels and activity assays. The broth was stored on ice until the protease could be purified. The MLBSP media used for the production of BLAP in shake flask cultures is described in Table 5.

Either kanamycin or tetracycline antibiotic stock solutions were added to the media just before use to a final concentration of 20 .mu.g/ml and 15 .mu.g/ml respectively.

Fermentation broth of transformed B. subtilis DB104, while still in the fermenter, was adjusted to pH 5.8 with 4N H.sub.2 SO.sub.4. The broth was collected and cooled to 4.degree. C. If not mentioned otherwise, all subsequent steps were performed on ice or at 4.degree. C. An aliquot of the broth material was clarified by centrifugation at 15,000.times.g.sub.av. for 60 min. Floating lipid material was removed by aspiration, and the supernatant filtered through Miracloth. The dark brown solution was placed in dialysis tubing (Spectrapor; #1, 6 to 8 kilodalton (kDa) molecular-weight-cut-off, 1.7 ml/cm) and dialyzed for 16 hours in 20 mM 2-(N-morpholino)ethanesulfonic acid (MES) containing 1 mM CaCl.sub.2, adjusted with NaOH to pH 5.8 (`MES buffer`). The dialysate was clarified by centrifugation (20,000.times.g.sub.av. for 10 min) and the pH of the solution was adjusted to 7.8 with 2N NaOH. The enzyme solution containing approximately 0.9 g of protein in 1.2 liter was loaded at a flow rate of 150 ml/hour onto a column of S-Sepharose Fast Flow (SSFF, Pharmacia; 25 mm diameter, 260 mm long) previously equilibrated with 20 mM N-(2-hydroxyethyl)piperazine-N'-(2-ethanesulfonic acid) [HEPES], containing 1 mM CaCl.sub.2, adjusted with NaOH to pH 7.8 (`HEPES buffer`). After the application of the enzyme solution the column was washed with 2 column volumes (250 ml) of HEPES buffer and then developed at a flow rate of 140 ml/hour with a gradient of 0 to 0.25 M NaCl in 600 ml of HEPES buffer. The gradient eluate was fractionated into 5.2-ml aliquots which were collected into tubes containing 2 ml of 100 mM MES/Na.sup.+, pH 5.8. The enzyme eluted between 0.12 and 0.15 M NaCl. Fractions containing the enzyme were pooled and protein was precipitated with ammonium sulfate at 52% of saturation. Solid salt (0.33 g per ml of solution) was added slowly with stirring over a period of 15 min, and stirring was continued for another 15 min. The precipitate was collected by centrifugation, the pellet was dissolved in MES buffer and the protein concentration in the solution was adjusted to 5 to 7 mg/ml. Following dialysis for 16 hours in MES buffer the solution was clarified by centrifugation and the pH of the supernatant was adjusted to 7.2. The protease was purified further by a second cation exchange separation on SSFF. All steps of this procedure were the same as above except that the pH of the HEPES buffer was 7.2 and that the NaCl gradient was from 0 to 0.25 M in 600 ml of HEPES buffer. Protein in pooled fractions was precipitated as above the ammonium sulfate and the enzyme was stored as ammonium sulfate precipitate at -70.degree. C. Prior to use the ammonium sulfate precipitate of the enzyme was dissolved in an appropriate buffer, typically MES buffer, at the desired protein concentration, and dialyzed overnight in the buffer of choice.

Fermentation broth from shake flasks, on average 180 ml, was collected and clarified by centrifugation at 20,000.times.g.sub.av. for 15 min. The supernatant was placed, with stirring, on ice and after 30 min the pH of the solution was adjusted to 5.8 with glacial acetic acid. If not mentioned otherwise, all subsequent steps were performed on ice or at 4.degree. C. The solution was clarified again by centrifugation (20,000.times.g.sub.av. for 15 min) and was concentrated approximately 4-fold by ultrafiltration (Amicon; YM30 membrane). The dark brown solution was placed in dialysis tubing (Spectrapor; #1, 6 to 8 KDa molecular-weight-cut-off, 1.7 ml/cm) and dialyzed for 16 hours in 20 mM HEPES/Na.sup.+, pH 7.8, containing 1 mM CaCl.sub.2 (`HEPES buffer`). The dialysate was clarified by centrifugation (20,000.times.g.sub.av. for 10 min) and the pH of the solution, if necessary, was adjusted to 7.8 with 2N NaOH. The enzyme solution was loaded at a flow rate of 60 ml/hour onto a column of SSFF (15 mm diameter, 75 mm long), previously equilibrated with HEPES buffer. When all colored by-products were eluted, the column was washed with 50 ml of HEPES buffer. Then, the enzyme was eluted with 0.25 M NaCl in HEPES buffer. Fractions of 1.2 ml were collected into tubes containing 0.5 ml of 100 mM MES/Na.sup.+, pH 5.8. Protein content in fractions was monitored either by a UV detector set at 280 nm or by protein assay as described below. Pooled fractions containing protease protein were placed on ice and protein was precipitated with a 5 to 8-fold volume excess of acetone at -20.degree. C. The protein was allowed to precipitate for 6 min, the mixture was centrifuged for 4 min at 6,600.times.g.sub.av., the supernatant was discarded, the pellet was briefly exposed to vacuum (water aspirator) to remove most of the acetone, and the pellet was dissolved in 20 mM MES/Na.sup.+, pH 5.8, to give an approximate protein concentration of 30 mg/ml. Prior to any assays, the solution was centrifuged in an Eppendorf centrifuge for 3 min at full speed (13,000.times.g.sub.max.).

Protein was determined by a modified biuret method (Gornall, A.G., et al. (1948) J. Biol. Chem. 177:751-766). The protein in a total volume of 500 .mu.l was mixed with 500 .mu.l of biuret reagent and incubated for 10 min at 50.degree. C. The solution was briefly chilled and its absorbance was measured at 540 nm. Typically, a reagent blank and three different protein aliquots in duplicates were measured and the recorded optical densities analyzed by linear regression. Bovine serum albumin (BSA, crystalline; Calbiochem) was used as protein standard. With purified BLAP protein the usefulness of BSA as protein standard in the biuret assay was confirmed. A BLAP sample was exhaustively dialyzed in 1 mM sodium phosphate, pH 5.8, and subsequently lyophilized. A sample of the solid material was weighed, dissolved in 1 mM sodium phosphate, pH 5.8, and used to generate a standard curve for the biuret assay. From the actual difference in phosphate content (Black, M.J., and Jones, M.E. (1983) Anal. Biochem. 135:233-238) of the final protein solution and the nominally 1 mM sodium phosphate solution used to dissolve the protein, the contribution of phosphate to the weight of solid BLAP was estimated and used to correct the standard curve.

Two different protease assays were used. With the HPE method protease activity was established at a single concentration of case in (prepared according to Hammarsten; Merck, #2242) as substrate. In the AAPF-pNA assay initial ratesofsuccinyl-L-alanyl-L-alanyl-L-prolyl-L-phenylalanyl-p-nitroanilide (AAPF-pNA; Bachem) supported catalysis were used to determine the kinetic parameters K.sub.m, k.sub.cat, and k.sub.cat /K.sup.m.

Culture supernatants or solutions of purified proteases were diluted with chilled buffer (10 mMMES/Na.sup.+, pH 5.8) to give three different solutions with a protein concentration ratio of 1:3:5. The substrate solution contained 9.6 mg/ml case in, 24 mM Tris, and 0.4% (w/v) sodium tripolyphosphate, dissolved in synthetic tap water (STW; 0.029% (w/v) CaCl.sub.2.2H.sub.2 O, 0.014% (w/v) MgCl.sub.2.6H.sub.2 O, and 0.021% (w/v) NaHCO.sub.3 in deionized water) adjusted to pH 8.5 at 50.degree. C., prepared as follows. With stirring for 10 min, 6 g of case in was dissolved in 350 ml of STW. To this, 50 ml of 0.3 M Tris in STW was added and stirring was continued for another 10 min. This solution was heated to 70.degree. C., then allowed to cool slowly At 50.degree. C., the pH was adjusted to 8.5 with 0.1N NaOH. When the solution reached room temperature, the volume was adjusted to 500 ml with STW, followed by the addition of 125 ml of 2% (w/v) pentasodium tripolyphosphate in STW, pH 8.5 (adjusted with 3N HCl). The protease assay was started by adding 50 .mu.l of protease solution to 750 .mu.l of substrate solution placed in a 2.2 ml Eppendorf container preincubated for 10 min at 50.degree. C. After 15 min, the reaction was terminated by the addition of 600 .mu.l of trichloroacetic reagent (0.44 M trichloroacetic acid, 0.22 M sodium acetate in 3% (v/v) glacial acetic acid). The mixture was placed on ice for 15 min, the precipitated protein removed by centrifugation for 8 min (at 13,000.times.g.sub.max.) and a 900 .mu.l aliquot of the supernatant was mixed with 600 .mu.l of 2N NaOH. The absorbance at 290 nm of this solution was recorded. Each dilution was assayed in duplicates and the data points for three different dilutions from one enzyme sample was analyzed by linear regression. A slope of 1 in this assay corresponds to 80 HPE units in the least diluted sample. In case of strongly colored culture supernatants with measurable quantities of UV absorbing material carried over by the diluted protease aliquot into the assay cuvette a control curve was constructed whose slope was subtracted from the slope of the protease assay before final HPE units were calculated.

Protease samples were diluted with 50% (v/v) 1,2-propanediol in 100 mM Tris, adjusted with 2N HCl to pH 8.6 at 25.degree. C. (`Tris-propanediol buffer`), in which they were stable for at least 6 h at room temperature. A stock solution of 160 mM AAPF-pNA was prepared in dimethylsulfoxide dried with a molecular sieve (Aldrich; 4 .ANG., 4-8 mesh) for at least 24 h prior to use. Fixed point assays were performed at 25.degree. C. with 1.6 mM AAPF-pNA in 100 mM Tris, adjusted with 2N HCl to pH 8 6 at 25.degree. C., in a total volume of 1.020 ml. The substrate was added to the assay buffer 1 min prior to the assay initiation and the reaction was started by addition of enzyme at a final concentration of 20 ng to 1.3 .mu.g of protein per ml (0.75 to 48.5 nM enzyme) depending on specific activity. Release of p-nitroanilide was monitored at 410 nm, and a molar extinction coefficient of 8,480 M.sup.-1 cm.sup.-1 was used to calculate amount and concentration of product formed (DelMar, E.G., et al. (1979) Anal. Biochem. 99:316-320). Kinetic parameters were calculated from a velocity vs. substrate concentration plot constructed from initial rates measured once each at 12 different AAPF-pNA concentrations ranging from 0.16 to 3.2 mM. Data were fitted to a hyperbolic curve and proportionally weighted using the program ENZFITTER (Leatherbarrow, R.J. (1987) ENZFITTER, Biosoft, Cambridge, UK). A nominal molecular weight of 26.8 kDa was used in all calculations that required the interconversion of protein concentration and molarity of protease enzyme.

Stability of protease proteins was evaluated under two different conditions: (a) 100 mM glycine/Na.sup.+, pH 10 at 60.degree. C., and (b) 100 mM glycine/Na.sup.+, pH 11 at 50.degree. C. At t=0 min, the protein was diluted to approximately 0.25 mg/ml into incubation buffer maintained at the desired temperature. Periodically, an aliquot was removed from this incubation mixture and diluted into Tris-propanediol buffer chilled on ice. Residual protease activity was determined by the AAPF-pNA assay at a fixed AAPF-pNA concentration (1.6 mM). Stability is expressed as half-life (t.sub.1/2) of activity determined from semi-logarithmic plots of residual activity as function of time. Each plot consisted of 6 data points with t.sub.1/2 approximately in the center between experimental points.

SDS was selected as representative of surfactants in general. Resistance of proteases to SDS was evaluated under two different conditions: (a) 100 mM Tris adjusted with 2N HCl to pH 8.6 at 50.degree. C., containing 1% (w/v) SDS, and (b) 50 mM sodium carbonate, pH 10.5 at 50.degree. C., containing 1% (w/v) SDS. Protease proteins were incubated at a final protein concentration of 0.25 mg/ml. Data were collected and evaluated as described above under Example 10.

Purity of protease samples was evaluated on 20% nondenaturing PhastSystem gels (Pharmacia) run with reversed polarity. The same system was used to monitor the protease content of crude shake flask and fermentation broths. Buffer strips were prepared as described in Application File No. 300 (Pharmacia).

Molecular weight determinations were performed on 20% SDS PhastSystem gels, using the following markers: bovine serum albumin, 66 kDa; egg albumin, 45 kDa; glyceral-dehydephosphate dehydrogenase, 36 kDa; carbonic anhydrase, 29 kDa; trypsinogen, 24 kDa; trypsin inhibitor, 20.1 kDa; .alpha.-lactalbumin, 14.2 kDa (all from Sigma). Prior to SDS-PAGE, a protease sample was denatured with formic acid at a final concentration of 30 to 50% (v/v). Upon dilution of formic acid to 15% (v/v) protein was precipitated with trichloroacetic acid at a final concentration of 10% (v/v). The collected pellet was washed once with water, then dissolved in 2% (w/v) SDS and heated for 2 min in a boiling waterbath. Gels were stained with Coomassie Brilliant Blue R-250 (Kodak).

Living cultures of the following have been accepted for deposit under the Budapest Treaty on the International Recognition of the Deposit of Microorganisms for the purposes of patent procedure by the American Type Culture Collection, 12301 Parklawn Drive, Rockville, Md. 20852 on May 8, 1991 (the accession number preceeds each deposit description): ATCC 68614--Bacillus licheniformis ATCC 53926 strain which contains a tetracycline-resistance plasmid originally derived from Bacillus plasmid pBC16 which carries the ATCC 53926 alkaline protease-BLAP ClaI fusion gene, whose structural gene has the mutations S3T, V4I, A188P, V193M, V199I; ATCC 68615--E. coli WK6 which carries phasmid pMc13C, a chloramphenicol-resistant derivative of phasmid pMc-5-8, that contains the ATCC 53926 alkaline protease- BLAP ClaI fusion gene and a 164 bp KpnI fragment carrying the ATCC 53926 alkaline protease gene's transcriptional terminator. The genotype of strain WK6 are .DELTA.lac-proAB, galE, strA, mutS::Tn10/F'lacI.sup.q, Z.DELTA.M15, proA.sup.+ B.sup.+ (Zell, R., and Fritz, H. -J. (1987) EMBO J. 6:1809-1815); ATCC 68616--E. coli GM33 which carries plasmid pCB13C, an ampicillin-resistant derivative of Pharmacia plasmid vector pTZ19R (Pharmacia) that contains the ATCC 53926 alkaline protease-ClaI fusion gene. The GM33 strain's genotype is dam3 (dam-methylase minus (Marinus, M.G. and Morris, N.R. (1974) J. Mol. Biol. 85:309-322)); ATCC 68617--E. coli WK6 which carries phasmid pMa5-8, an ampicillin-resistant mutagenesis vector described in Stanssens, P. et al. (1989) Nucleic Acids Research 17:4441-4454. The genotype of strain WK6 mutations are .DELTA.lac-proAB, galE, StrA, mutS::Tn10/F'lacI.sup.q, Z.DELTA.M15, proA.sup.+ B.sup..sup.+ (Zell, R., and Fritz, H. -J. (1987) EMBO J. 6:1809-1815); ATCC 68618--an E. coli WK6 which carries phasmid pMc5-8, a chloramphenicol-resistant mutagenesis vector described in Stanssens, P., et al. (1989) Nucleic Acids Res. 17:4441-4454. The genotype of strain WK6 are .DELTA.lac-prOAB, galE, strA, mutS::Tn10/F'lacI.sup.q, Z.DELTA.M15, proA.sup.+ B.sup.+ (Zell, R., and Fritz, H. -J. (1987) EMBO J. 6:1809-1815).