Serine Protease and Uses Thereof

Cell-mediated killing by cytotoxic lymphocytes is an important immunologic defense against tumor cell proliferation, viral infection and transplanted tissue (Duke, R. C., et al. J. Exp. Med. 170:1451-1456 (1989)). Cytotoxic lymphocyte--mediated lysis is often associated with the formation of membrane lesions on target cells caused by exocytosis of cytoplasmic granules from cytolytic lymphocytes (Henkart, P. A., et al. J. Exp. Med. 160:75-93 (1984); Joag, S., et al. J. Cell Biochem. 39:239-252 (1989 )).

These granules contain proteoglycans (MacDermott, R. P., et al. J. Exp. Med. 162:1771-1787 (1985)) and several proteins (Tschopp, J., and Johngeneel, C. V. Biochemistry 27:2641-2646 (1988); Shinkai, Y., et al. Nature 334:525-527 (1988); Lichtenheld, M. G., et al. Nature 335:448-451 (1988); Tschopp, J., and Nabholz, M. Annu. Rev. Immunol. 8:279-302 (1990); Liu, C-C., et al. Cell 51:393-403 (1987); Tian, Q., et al. Cell 67:629-639 (1991)), including serine proteases (SP) (Tschopp, J., and Johngeneel, C. V. Biochemistry 27:2641 -2646 (1988)) and pore-forming protein (cytolysin) (PFP) (Shinkai, Y., et al. Nature 334:525-527 (1988); Lichtenheld, M. G., et al. Nature 335:448-451 (1988); Tschopp, J., and Nabholz, M. Annu. Rev. Immunol. 8:279-302 (1990)). PFP forms transmembrane ionic pores that produce membrane damage (Young, J. D. Physiol. Rev. 69:250-314 (1989); Ojcius, D. M., et al. Proc. Natl. Acad. Sci. USA 88:4621-4625 (1991)) but does not cause DNA fragmentation (Duke, R. C., et al. J. Exp. Med. 170:1451-1456 (1989)).

A direct role for SP in cytolysis has not been universally accepted (Henkart, P. A., et al. J. Immunol. 139:2398-2405 (1987); Berke, G. Immunol. Lett. 20:169-178 (1989); Ostergaard, H. L. and Clark, W. L. J. Immunol. 143:2120-2126 (1989)), despite the fact that a number of protease inhibitors can block cytotoxic T lymphocyte (CTL) --mediated lysis (Chang, T. W., and Eisen, J. E. Nature 124:1028-1033 (1980); Hudig, D., et al. J. Immunol. 147:1360-1368 (1991)). DNA fragmenting properties have been postulated for two members of the SP family (Munger, W. E., et al. Immunol. Rev. 103:99-109 (1988); Shi, L., et al. J. Exp. Med. 175:553-566 (1992)) when combined with PFP. Alternatively, it has been suggested that granules break down various extracellular matrix proteins (Simon, M. M., et al. Immunol. 60:219-230 (1987); Sayers, T. J., et al. J. Immunol. 148:292-300 (1992)) and may therefore be involved in the in vivo trafficking of NK cells and CTL or in modifying effector cell:target interactions.

Several serine protease genes from CTL and NK cells have been isolated and sequenced by several different laboratories (Zunino, et al. Biochem. Biophys. Acta. 967:331-340 (1988); Lobe, C. G., et al. Proc. Natl. Acad. Sci. USA 83:1448-1452 (1986); Lobe, C. G., et al. Science 232:858-861 (1986); Gershenfeld, H. K., and Weissman, I. L. Science 232:854-858 (1986); Jenne, D. E., and Tschopp, J. Immunol. Rev. 103:53-71 (1988); Brunet, J-F., et al. Nature 322:268-271 (1986); Kwon, B. S., et al. D-E. J. Exp. Med. 168:1839-1854 (1988); Schmid, J., and Weissman, C. J. Immunol. 139:250-256 (1987); Gershenfeld, H. K., et al. Proc. Nat'l Acad. Sci. USA 85:1184-1185 (1988); Manyak, C. L., et al. J. Immunol. 142:3703-3713 (1989); Zunino, S. J., et al. J. Immunol. 144:2001-2009 (1990)).

Some of these CDNAs encode the same protein, but seven different serine proteases have been identified. Seven serine proteases, granzymes A, B, C, D, E, F, and G, have been isolated and purified from murine granules (Maseon, D. and Tschopp, J. Cell 49:679-685 (1987)). Murine granzyme A is also known as Hanukah factor (Gershenfeld, H. K., and Weissman, I. L. Science 232:854-858 (1986)), TSP-1 (Simon, M. M., et al. Immunol. 60:219-230 (1987)), BLT-esterase (Pasternak, M. S., et al. Nature 314:743-745 (1985)), CTLA-3 (Brunet, J-F., et al. Nature 322:268-271 (1986)); and SE1 (Young, J. E.-E., et al. Cell 47:183-194 (1986)); murine granzyme B as CCP1 (Lobe, C. G., et al. Science 232:858-861 (1986)); and CTLA-1 (Brunet, J-F., et al. Nature 322:268-271 (1986)); granzyme C (Masson, D. and Tschopp, J. Cell 49:679-685 (1987)) as CCP2 (Lobe, C. G., et al. Science 232:858-861 (1986)); granzyme E as CCP3 (Bleackley, et al. FEBS Lett. 234:153-159 (1988)); and granzyme F as CCP4 (Bleackley, et al. FEBS Lett. 234:153-159 (1988)).

Granzymes A and B also have been isolated from human CTL granules and are homologous to the murine enzymes (Fruth, U., et al. Eur. J. Immunol. 17:1625-1633 (1987); Poe, M., et al. J. Biol. Chem. 266:98-103 (1991)). Human granzyme A is also known as HuTSP (Fruth, U., et al. Eur. J. Immunol. 17:1625-1633 (1987)), Hanukah factor (Gershenfeld, H. K., et al. Proc. Nat'l Acad. Sci. USA 85:1184-1185 (1988)), CTL tryptase (Poe, M., et al. J. Biol. Chem. 263 (26):13215-13222 (1988)), and granzyme 1 (Hameed, A., et al. J. Immunol. 141:3142-3147 (1988)); and human granzyme B as HLP (Schmid, J., and Weissman, C. J. Immunol. 139:250-256 (1987)), HSE26.1 (Trapani, J. A., et al. Proc. Nat'l. Acad. Sci. U.S.A. 85:6924-6928 (1988)), SECT (Caputo, A., et al. J. Biol. Chem. 263:6363-6369 (1988)), granzyme 2 (Hameed, A., et al. J. Immunol. 141:3142-3147 (1988)), and Q31 granzyme B (Poe, M., et al. J. Biol. Chem. 266:98-103 (1991)). Only one rat granzyme, RNKP-1, has been purified (Sayers, T. J., et al. J. Immunol. 148:292-300 (1992)) and sequenced (Zunino, S. J., et al. J. Immunol. 144:2001-2009 (1990)).

Thus far, the hydrolytic activities for only three enzymes, Tryptase, Chymase, and ASP-ase, encoded by the seven serine protease genes have been described. Granzymes A and F have been shown to exhibit tryptase activity (Jenne, D. E., and Tschopp, J. Immunol. Rev. 103:53-71 (1988); Jiang, S., et al. Protein Expression Purification 1:77-85 (1990)); granzyme B has shown predominantly ASP-ase activity and some Met-ase activity ( Odake, S., et al. Biochemistry 30:2217-2227 (1991); Poe, M., et al. J. Biol. Chem. 266:98-103 (1991)); and granzymes D, E, and F were predicted to have chymase activity (Odake, S., et al. Biochemistry 30:2217-2227 (1991)). Granzymes C and G, although tested, have not been shown to exhibit a specific enzymatic activity (Odake, S., et al. Biochemistry 30:2217-2227 (1991)). RNKP-1 has been shown to have ASP-ase activity.

With respect to the Met-ase activity exhibited by granzyme B, Odake, et al. suggested that this activity may belong to granzyme B because of the observation that the Met-ase and Asp-ase activities coelute from the Mono S column and the nearly identical inhibition rates of granzyme B with DCI when three different substrates are used. On the other hand, Odake, et al. stated that the observation by Poe, et al. (Poe, M., et al. J. Biol. Chem. 266:98-103 (1991)) that the Met-ase activity was separated from the Asp-ase activity during the purification of human granzyme B suggests the presence of different enzymes.

Other than granzyme B, no cytolytic granule proteins have been reported which exhibit Met-ase activity.

This invention describes the biochemical purification of a novel 30 kDa SP with Met-ase activity (RNK Met-1) from the cytolytic granules of the rat RNK-16 LGL leukemia. Isolation and sequencing of the cDNA encoding RNK Met-1 from a rat RNK-16 .lambda.gt-11 library reveals RNK Met-1 to be a unique SP gene with structural variations that distinguish it from other members of the SP family. The invention also describes the human serine protease and its cDNA clone obtained by screening the phage .lambda.gt-10 cDNA library from human Lopez LGL leukemia with the rat RNK-Met-1 cDNA clone.

The present invention provides a purified and isolated nucleic acid molecule encoding serine protease (Met-ase) having Met-ase activity but not Asp-ase activity and a molecular weight of about 30,000 daltons on SDS PAGE under reducing and non-reducing conditions. The present invention also provides a vector comprising this nucleic acid molecule, a prokaryotic or eukaryotic host cell stably transformed or transfected with the vector, as well as a method for detecting this nucleic acid in a sample.

FIGS. 1A and 1B. Separation of granule constituents on an ACA 54 column. Fractions were extensively dialysed against PBS and tested for BLT-esterase activity (.quadrature.--.quadrature.) or Met-ase activity ( -- ) by assaying the change in O.D..sub.410 /10 min caused by 50 .mu.l of each fraction (FIG. 1A). Cytolysin (PFP) activity (.largecircle.--.largecircle.) in units/ml was assayed as described in the Materials and Methods (FIG. 1A). The elution peaks of molecular weight markers were fractions 79 (BSA, 67 kDa), 93 (ovalbumin, 43 kDa), 121 (chymotrypsinogen, 25 kDa) and 134 (ribonuclease, 13.7 kDa). The O.D.280nm ranged from 0.00-0.02 (FIG. 1B).

FIG. 2. Isolation of the Met-ase on reverse phase HPLC. For enzymatic analysis an aliquot of each fraction was lyophilized to dryness in the presence of 50.mu.g of BSA, reconstituted in PBS and extensively dialysed against PBS. An aliquot of fraction 104 which contained most of the Met-ase activity was lyophilized to dryness and then sequenced using the Edman degradation procedure.

FIGS. 3A and 3B. PAGE of HPLC purified rat granule serine proteases under reducing (FIG. 3A) or non-reducing (FIG. 3B) conditions. Asp-ase (lane a), Tryptase (lane b) and Met-ase (lane c). The positions of the molecular mass standards 46, 30, 21 and 14 kDa are shown.

FIGS. 4A and 4B. Nucleotide and predicted amino acid sequences (SEQ ID NO:1 and SEQ ID NO:2, respectively) of RNK-Met-1. Nucleotide sequence is numbered from the first nucleotide of the cloned 867 bp cDNA insert. Amino acid sequence encoded by this clone is shown by standard abbreviations below the respective DNA sequence. The numbering of the amino acid sequence starts with the amino-terminal residue (+1) of the mature RNK-Met-1 protein as determined by amino acid sequencing. The partial protein sequence determined for the amino terminus of RNK-Met-1 is underlined. The residues forming the catalytic site of SP are boxed (.quadrature.) and all cysteine residues are circled (.largecircle.). The putative N-linked glycosylation sites are marked by dashed underline (---) and the combination of amino acid residues thought to determine the specificity of the substrate binding pocket are asterisked (*). The stop codon is denoted (.DELTA.) and polyadenylation signal sequence in the 3' non coding region is underlined.

FIGS. 5A and 5B. Northern blot analysis of RNK-Met-1 expression. Total cellular RNA was isolated from the following tissues and cell lines (as described in the Materials and Methods): FIG. 5A; (1) rat CRC.sup.+ RNK-16 NK leukemia (in vitro), (2) rat CRC.sup.- RNK-16 NK leukemia (in vitro), (3) normal rat liver, (4) normal rat colon, (5) normal rat brain, (6) rat RNK-16 NK leukemia (in vivo--passage 7), (7) human HuT 78 T cell lymphoma, (8) human YT LGL leukemia (9) gibbon MLA 144 lymphoma, (10) mouse CTLL R8 cytotoxic T cell clone, (11) human Lp NK leukemia and (12) mouse P815 mastocytoma; FIG. 5B; (1) normal rat spleen (unseparated), (2) normal rat splenocytes (nylon wool passed), (3) normal rat thymocytes, (4) normal rat thymocytes treated with PMA (20 ng/ml) and IL-2 (1000 U/ml) for 4 days and (5) normal rat A-LAK splenocytes (see Materials and Methods). Northern blot analysis was performed on 25 .mu.g of RNA and the filters were sequentially hybridized with .sup.32 P-labeled cDNA probes for: rat RNK-Met-1 (exposure, 2 days) and human .gamma.-actin (exposure, 1 day).

FIGS. 6A and 6B. Nucleotide and predicted amino acid sequences (SEQ ID NO:3 and SEQ ID NO:4, respectively) of human Met-ase.

The present invention provides a purified and isolated serine protease (Met-ase) having Met-ase activity but not Asp-ase activity and a molecular weight of about 30,000 daltons on SDS PAGE under reducing and non-reducing conditions.

The protease of the present invention is purified to homogeneity sufficient to be sequenced and is at least about 90% pure. At this purity level, the protease has a Met-ase activity of about 156 nM/sec/.mu.g without the intentional addition of other substances such as other proteins or carriers. The assay for measuring this activity was performed as described in the Experimental Details section. The specific activity, however, depends on the degeneracy and folding of the protease and may be as low as about 100 nM/sec/.mu.g to as high as about 200 nM/sec/.mu.g.

In the preferred embodiment, the protease has the amino acid sequence selected from the group consisting of: (a) the amino acid sequence contained in FIGS. 4A and 4B (SEQ ID NO:2); (b) the amino acid sequence contained in FIGS. 6A and 6B (SEQ ID NO:4); and (c) biologically active fragments or analogs of the amino acid sequence defined in (a) or (b). The serine protease of the present invention encompasses both the rat and human forms as well as proteases having the same characteristics and Met-ase activity from other mammalian sources.

The present invention also provides a purified and isolated DNA molecule comprising a DNA sequence encoding the protease hereinabove. The DNA molecule includes all DNA sequences which encode for the protease including all degenerate forms. In the preferred embodiment, the DNA molecule comprises a DNA sequence selected from the group consisting of: (a) the DNA sequence contained in FIGS. 4A and 4B (SEQ ID NO:1) or a complementary strand thereof; (b) the DNA sequence contained in FIGS. 6A and 6B (SEQ ID NO:3) or a complementary strand thereof; (c) DNA sequences which hybridize to the DNA sequence defined in (a) or (b), or fragments thereof; and (d) DNA sequences, but for the degeneracy of the genetic code, would hybridize to the DNA sequences defined in (a), (b), or (c).

The present invention also provides an antibody immunoreactive with the protease hereinabove. The antibody may be polyclonal or monoclonal. If polyclonal, the antibody may be produced by immunizing a rabbit, mouse or rat with the protease or fragment thereof as an immunogen and collecting the serum produced thereby. The protease or fragment therof may be coupled to a protein such as keyhole limpet hemocyanin (KLH) or bovine serum albumin (BSA), with or without an adjuvant. A booster injection should be give 4-6 weeks after the primary injection. Additional booster injections may be given at later periods if necessary. The presence of antibody in the serum may be tested by radioimmunoassay (RIA), enzyme-linked immunosorbent assay (ELISA), or immunoprecipitation. To produce monoclonal antibodies, the spleen cells from the rabbit, mouse or rat are removed and fused with a myeloma cell, grown in culture, then inserted into a hybridoma to produce the desired monoclonal antibody by standard procedures.

The antibody of the present invention may then be used in detecting the protease in a sample or in the purification of recombinant protease from a recombinant host. For detection purposes, the antibody may be labeled with a detectable marker, including but not limited to a fluorescence, enzyme or radiolabeled marker known to those skilled in the art. The labeled antibody (polyclonal or monoclonal) may then be used to detect the protease of the present invention in a biological sample by using standard technology such as solid phase radioimmunoassay (e.g. competition RIAs, immobilized antigen or antibody RIAs, or double antibody RIAs), immunoprecipitation, or Western blotting.

The present invention also provides a method for detecting nucleic acid encoding the protease hereinabove (Met-ase) in a sample which comprises contacting nucleic acid from the sample with the DNA molecule hereinabove labeled with a detectable marker (as described above) under conditions permitting the nucleic acid to hybridize with the labeled DNA molecule, determining that hybridization has occurred, and thereby detecting nucleic acid encoding Met-ase in the sample.

The sample is a biological cell tissue or fluid sample from a mammalian subject and preferably is human. The sample is preferably from a tumor and is removed by standard biopsy procedures. The nucleic acid from the sample is then removed by procedures known to those in the art such as phenol/chloroform/ethanol extraction or guanidine thiocyanate. The nucleic acid may be DNA or RNA.

The labeled DNA molecule is contacted with the nucleic acid from the sample under hybridizing conditions. Hybridization of the two nucleic acids is determined by procedures known to those skilled in the art and is a function of the marker employed (e.g. fluorescent, enzyme or radiolabeled marker). The protease is detected in the sample when hybridization has occurred.

The protease also may be detected in the sample using polymerase chain reaction (U.S. Pat. Nos. 4,683,200 and 4,683,195 and Perkin Elmer/Cetus kit). The oligonucleotide primers based on the DNA sequence hereinabove are synthesized by standard techniques (e.g. H-phosphate method, dideoxy method, etc.). If the nucleic acid from the sample is RNA, it must first be converted to cDNA using reverse transcriptase (Perkin Elmer/Cetus Reverse Transcriptase kit). The DNA or CDNA is then subjected to PCR amplification using the synthesized primers. The protease is present in the sample if PCR amplification occurs.

Following PCR, the presence of the protease may be detected further using electrophoresis or other techniques.

The present invention also provides the protease hereinabove produced by recombinant techniques (see U.S. Pat. Nos. 4,704,362, 4,366,246, 4,425,437, 4,356,270, and 4,571,421). Specifically, the protease DNA is placed into a vector (e.g. plasmid, bacteriophage .lambda., or cosmid vector) by standard techniques. The vector containing the protease DNA is then stably tranformed or transfected in a microbial mammalian expression system which recombinantly produces the protease. The expression system is preferably a prokaryotic (pGEX, pPOW) or eukaryotic (CDM8, pSVL, vaccinia, or baculovirus) cell host. The host cells are then screened for clones which produce the recombinant serine protease. The present invention also provides a recombinant DNA molecule comprising the DNA molecule hereinabove operably linked to an expression-linked control sequence.

The following Experimental Details Section sets forth specific examples to aid in an understanding of the invention, and should not be construed to limit in any way the invention as defined in the claims which follow thereafter.

A. Materials and Methods.

Abbreviations: SP, serine protease; LGL, large granular lymphocyte(s); PFP, pore-forming protein (cytolysin); Hepes, N-2-hydroxyethylpiperazine-N'-2-ethane sulfonic acid; BLT, .alpha.-N-benzloxycarbonyl-L-lysinethiobenzylester; DTNB, 5,5'- dithiobis-(2-nitrobenzoic acid); Bzl, benzyl; PCR, polymerase chain reaction; PMA, phorbol myristate acetate; PEG, polyethylene glycol.

Rats/RNK tumors. Tumor cells from the rat large granular lymphocyte leukemia (RNK) were kindly provided by Dr. C. Reynolds (BRMP, FCRDC, Frederick, MD). RNK tumors were serially passaged in vivo in Fischer (F344) rats. Most of the tumor cells were from the RNK-16 line (passages 6-13) in ascites form.

Purification of Cytoplasmic Granules. The procedure for purification of cytoplasmic granules of rat LGL tumors has previously been described in detail (Millard, P. J., et al. J. Immunol. 132:3197-3204 (1984)). Briefly, RNK cells (5.times.10.sup.9 -1.times.10.sup.10) were washed in Hank's balanced salt solution (HBSS) and resuspended at 1.times.10.sup.8 cells/ml in disruption buffer (0.25M Sucrose, 0.01M N-2-hydroxyethylpiperazine-N'-2-ethane sulfonic acid (Hepes), 4 mM EGTA, 1000 U/ml Heparin [Sigma Chemical Co., St. Louis, Mo.] pH7.4). Cells were lysed by decompression at 0.degree. C. after equilibrating at 450 psi nitrogen for 20 min. After the addition of MgCl.sub.2 to 5 mM, the homogenate was digested with DNase 1 (800 .mu./ml, 22.degree. C., 30 min). Nuclei were removed by filtration through Nucleopore filters (Nucleopore Corp., Pleasanton, Calif.) of 5 and 3.mu.m and the resulting homogenate was cooled at 0.degree. C. Aliquots of 5 ml were layered onto 20 ml of 48% Percoll (in disruption buffer without heparin) and centrifuged on a 50.2 Ti rotor at 29,000 rpm (70,000 g) for 30 min at 4.degree. C. on a Beckman L 5-50B ultracentrifuge (Beckman Instruments, Fullerton, Calif.). Fractions (1 ml) of purified granules were localized to a visible band near the bottom of the tubes. The success of fractionation was monitored by assaying .alpha.-N-benzyloxycarbonyl-L-lysine-thiobenzylester (BLT)-esterase activity and the granule containing fractions were pooled and Percoll removed by centrifugation (100,000 g, 3 h). Granules were recovered as a loose white pellet over a hard Percoll pellet and stored at -70.degree. C.

Purification of Granule RNK Met-1. Dense granules combined from 6-10 isolations were solubilized by suspension in 2M NaCl to give a final volume of 20 ml in ACA column buffer (PBS diluted 1:1 with 10 mM Hepes, pH 7.4 containing 2M NaCl, 0.5 mM EGTA). The mixture was rapidly freeze--thawed twice and subjected to centrifugation (100,000 g, 3 h) to remove insoluble material. This extract was sterile filtered through a 0.45.mu.m Nalgene filter (Nalge Company, Rochester, N.J.) and concentrated to a total volume of 10-15 ml using centricon 10 concentrators (Amicon, Danvers, Mass.) that have a molecular weight cut-off of 10 kD. The soluble extract was fractioned by gel filtration on an Ultrogel ACA 54 column (IBF Biotechnics Inc., Savage, Md.) 80 cm.times.5 cm and 8 ml fractions were collected. Fractions were concentrated and extensively dialyzed against PBS, pH7.2 (Spectra/Por 7, Spectrum Medical Industries Inc., Los Angeles, Calif.) (cut off 15 kDa). Individual fractions were then tested for protease activity, BLT-esterase activity, and cytolysin activity (see below). Column fractions containing the majority of the granule Met-ase activity were pooled and concentrated to about 4 mls (Centricon 10). The pooled Met-ase activity was exhaustively dialyzed against PBS, 0.2% polyethylene glycol (PEG) and further purified by heparin--agarose affinity chromatography (Pierce, Rockford, Ill.). A 1 ml prepacked column was equilibrated with PBS, 0.2% PEG, pH7.2 and then stepwise elutions were performed with column buffer containing 0.1, 0.3, 0.65 and 0.8M NaCl (.about.15 ml/elution). Fractions were made up to 30 ml with PBS, 0.2% PEG, 2M NaCl and concentrated to 2-4 ml (Centricon 10). Aliquots from each elution were extensively dialyzed against PBS and tested for BLT--esterase and protease activity.

Fractions containing the granule Met-ase activity were made up to 0.04M Tris-HCl., pH 7.4 by the addition of concentrated buffer, and 8M guanidine (Pierce). The resulting solution was injected onto a high-pressure liquid chromatograph (Waters Associates, Milford, Mass.) and separated by reverse phase HPLC on a .mu.-Bondapak C18 column (Waters Associates) as previously described (Henderson, L. E., et al. J. Virol. 52:492-500 (1984)). The column was equilibrated in 0.05% trifluoroacetic acid (TFA) and proteins were eluted using a linear gradient of acetonitrile and 0.05% TFA. Eluted proteins were detected by UV absorption at 206 nm with a model 2140 Rapid Spectral detector (LKB, Bromina, Sweden) and 2 ml fractions were collected. A small volume of BSA was added to aliquots from the HPLC column (100 .mu.g/ml) for stabilization. Solvents were removed by lyophilization. The lyophilate was reconstituted in PBS, 20% glycerol, pH 7.2 and dialyzed extensively against this buffer to promote protein renaturation. Aliquots were extensively dialyzed against PBS and tested for BLT-esterase and protease activity.

Gas-Phase Sequencing. Amino acid sequences were determined by the Edman degradation procedure as previously described (Hewick, R. M., et al. J. Biol. Chem. 256:7990-7997 (1981)) using a model 470 A Protein Sequencer (Applied Biosystems, Foster City, Calif.).

Gel Electrophoresis. Sodium dodecyl sulfate (SDS) -polyacrylamide electrophoresis (PAGE) was performed on 4-20% gradient gels (Novex, Encinitas, Calif.) by the method of Laemmli (Laemmli, V. K. Nature 227:680-685 (1970)). Proteins were visualized by 0.5% Coomassie Brilliant blue in 40% methanol/10% acetic acid. Low levels of protein were detected using silver staining (Daiichi Pure Chemicals Co., Ltd. Hyde Park, Mass.).

Assay of Proteases. Thiobenzylester substrates were used to measure protease activities. For monitoring enzyme activities from granules and column fractions, assays were performed at room temperature using 0.5 mM 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) (Sigma) to detect the HSBzl leaving group (e.sub.410 =13600M-.sup.-1 cm.sup.-1).

BLT-esterase activity was estimated using a microtiter assay (Green, G. D. J., and Shaw, E. Anal. Biochem. 93:223-226 (1979)). Briefly, 50 .mu.l of sample was added to 100 .mu.l of 1 mM DTNB, made up in 10 mM Hepes, 1 mM CaCl.sub.2, 1 mM MgCl.sub.2, pH7.2. The reaction was initiated by the addition of 50 .mu.l of BLT (Sigma) to give a final concentration of 500 .mu.M. For Metase determinations, 50 .mu.l of dilutions of the sample in 0.1M Hepes, 0.05M CaCl.sub.2, pH7.5 were added to 100 .mu.l of 1 mM DTNB and the reaction was initiated by the addition of 50 .mu.l of Boc-Ala-Ala-Met-S Benzyl (Bzl) to give a final concentration of 150 .mu.M. The duration of the assay depended on color development, the rate of which was measured (0.D.sub.410) on a Dynatech MR 5000 microplate reader. Controls of sample and DTNB alone or DTNB and substrate alone were run. For more sensitive comparisons of enzymatic activities, peptide thiobenzyl ester substrates were used to measure protease activities. The chymase substrate Suc-Phe-Leu-Phe-SBzl was purchased from BACHEM Bioscience Inc., Philadelphia, Pa. Z-Arg-SBzl (the tryptase substrate, Kam, C-M., et al. J. Biol. Chem. 262:3444-3451 (1987)); Boc-Ala-Ala-AA-SBzl (AA=Asp, Met, Leu, Nle, or Ser) and Suc-Ala-Ala-Met-SBzl (Odake, S., et al. Biochemistry 30:2217-2227 (1991); Harper, J. W., et al. Biochemistry 23:2995-3002 (1984)) were synthesized previously. Boc-Ala-Ala-Asp-SBzl is the substrate for Asp-ase and peptide thiobenzyl esters containing Met, Leu or Nle are substrates for Met-ase SP. Assays were performed at room temperature in 0.1M, Hepes buffer, pH7.5, containing 0.01M CaCl.sub.2 and 8% Me.sub.2 SO using 0.34 mM 4,4'-dithiodipyridine (Aldrithiol-4, Aldrich Chemical Co., Milwaukee, Wis.) to detect HSBzl leaving group that reacts with 4,4'-dithiodipyridine to release thiopyridone (.epsilon.324=19800M.sup.-1 cm.sup.-1, Grasetti, D. R. and Murray, J. F. Arch. Biochem. Biophys. 119:41-49 (1967)). The initial rates were measured at 324 nm using a Beckman 35 spectrophotometer when 10-25 .mu.l of an enzyme stock solution was added to a cuvette containing 2.0 ml of buffer, 150 .mu.l of 4,4'-dithiodipyridine and 25 .mu.l of substrate. The same volume of substrate and 4,4'-dithiodipyridine were added to the reference cell in order to compensate for the background hydrolysis rate of the substrates. Initial rates were measured in duplicate for each substrate concentration and were averaged in each case. Substrate concentrations were 100-133 .mu.M.

Cytolysin assays. Cytolysin (PFP) activity was measured using sheep E as targets (Henkart, P. A., et al. J. Exp. Med. 160:75-93 (1984)).

Screening of cDNA library. Two oligonucleotide primers were synthesized to PCR amplify a RNK-Met-1 cDNA probe from RNK-16 total cellular RNA. The 5'-3' primer was a degenerate inosine containing 41 mer (5'GAATTC.TAC(T)ATG GTI TCI CTI CAA(G) AAC(T) ACI AAA(G) TCI GAC(T) GT3') (SEQ ID NO:5 AND SEQ ID NO:6) coding for the Tyr-Met-Val-Ser-Leu-Gln-Asn-Thr-Lys-Ser-His-Met (pos. 14-25) (SEQ ID No:7) unique region obtained from sequencing the first 25 N-terminal amino acids of the RNK-Met-1 protein. The 3'-5'primer was a 21 mer (3'CTG AGA CCT CCC GGA.CTTAAG 5') (SEQ ID NO:8) coding for the Asp-Ser-Gly-Gly-Pro (SEQ ID NO:9) amino acid sequence around the active site Ser (pos. 183-187) that is conserved in SP proteins. EcoRI ends were included in these oligonucleotide primers for subcloning. Total cellular RNA was isolated as described below. RNA (1 .mu.g) was made up to 20 .mu.l in a reaction mixture [10 mM Tris-HCl buffer, pH 8.3, 50 mM KCl (Perkin-Elmer Cetus (PE-Cetus), Norwalk, Conn.) 5 mM MgCl.sub.2, 150 pmol random hexamers (Pharmacia Inc., Piscataway, N.J.), 200 U Murine Moloney Virus H Reverse Transcriptase (Bethesda Research Laboratories (BRL), Gaithersburg, Md.), 20 U RNAsin (Promega Corp., Madison, Wis.), and 1 mM of each dNTP]. cDNA synthesis was performed at 42.degree. C. for 15 min, 99.degree. C. for 5 min and 5.degree. C. for 5 min. For PCR amplification, samples were made up to a final 100 .mu.l reaction mixture (10 mM Tris-HCl buffer, pH 8.3, 50 mM KCl, 2 mM MgCl.sub.2, 100 pmol of both primers and 2 U Taq DNA polymerase (PE-Cetus)). Thirty PCR cycles were run for 1 min at 94.degree. C., 2 min at 50.degree. C., and 3 min at 72.degree. C. The PCR products were analyzed on a 3% NuSieve gel(FMC Bioproducts, Rockland, Me.). A 534 bp fragment amplified specifically from RNK-16 mRNA was gel purified on a DEAE cellulose membrane and subcloned into the EcoRI site of the vector pBluescript KS.sup.+.

This fragment was used to screen a RNK-16 cDNA library to isolate a full length clone. The cDNA library was made from rat RNK-16 tumor cell RNA at the National Institutes of Health (Bethesda, Md.) by Dr. Cho Yue using the Gubler and Hoffman method of cDNA synthesis (Gubler, U., and Hoffman, B. J. Gene 25:263-269 (1983)). Sequencing was performed in both orientations using the dideoxy method (Sanger, F., et al. Proc. Natl. Acad. Sci. USA 74:5463-5467 (1977)) and single stranded and double stranded templates (Chen, E. Y. and Seeburg, P. H. DNA 4:165-170 (1985)).

Northern Blot Analysis. Total cellular RNA was obtained from the following cell lines and tissues; murine P815 mastocytoma, murine CTLL-R8 cytotoxic T cell clone, human Lp NK leukemia, gibbon MLA 144 lymphoma, HuT 78 human T cell lymphoma, human U937 histiocytic lymphoma and the human YT LGL leukemia. Cells were cultured in RPMI 1640 medium supplemented with 10% heat-inactivated fetal calf serum, 2 mM glutamine, 100 U/ml penicillin and 100 .mu.g/ml streptomycin (Gibco Laboratories, Life Technologies, Grand Island, N.Y.). The in vitro RNK16 cell lines, CRC.sup.+ and CRC.sup.- were cultured in the above medium supplemented with 5.times.10.sup.-5 M 2-ME (Sigma) and 1 mM sodium pyruvate (Gibco). CRC.sup.+ additionally required 10% ConA treated T cell supernatant. In vivo RNK-16 tumor cells were obtained from serial ascites passage in Fisher (F344) rats. Normal rat spleens and thymuses were aseptically removed and single-cell suspensions prepared in RPMl 1640 with 10% heat-inactivated FCS. Splenic mononuclear cells were harvested after centrifugation on Ficoll/Hypaque gradients at 300 g for 20 min. Rat A-LAK splenocytes were prepared as described previously (Vujanovic, N. L., et al. J. Exp. Med. 167:15-29 (1988 )). Briefly, 10.sup.8 splenocytes in RPMI 1640, 10% FCS, were added to a 10 cc syringe containing 4 g of sterile nylon wool (1 h, 37.degree. C.) to reduce contaminating B cells and monocytes. The nylon non-adherent splenocytes were collected and washed. These splenocytes and thymocytes were cultured in the absence or presence of 20 ng/ml phorbol myristate acetate (PMA) (Sigma) and 1000 U/ml recombinant human IL-2 (Kindly provided by Cetus Corp., Emeryville, Calif.) for 4 days. Thymocytes were harvested and spleen A-LAK cells were obtained by culturing the plastic-adherent (A) splenocytes in the conditioned medium (4 days) for a further 2 days (Vujanovic, N. L., et al. J. Exp. Med. 167:15-29 (1988)). Total cellular RNA from normal rat brain, liver and colon was extracted by homogenizing the tissues in 5M guanidine thiocyanate.

Total cytoplasmic RNA was purified from all cells by the method of Chomczynski, et al (Chomczynski, P., and Sacchi, N. Anal. Biochem. 162:156-159 (1987)). For Northern analysis, 25 .mu.g RNA was subjected to electrophoresis on a 0.8% agarose formaldehyde gel, then transferred to Nytran (Schleicher and Schuell, Keene, N.H.). All blots were hybridized to .sup.32 P-labeled RNK-Met-1 cDNA and human .gamma.-actin (Gunning, P., et al. Mol. Cell. Biol. 3:787-795 (1983)) cDNA as described previously (Thomas, P. S. Methods Enzymol. 100:255-266 (1983)). The blots were then exposed to Kodak X-OMAT AR film for 0-7 days at -70.degree. C.

Human Met-ase. A cDNA clone encoding a human T cell and large granular lymphocyte (LGL)-specific serine protease was obtained by screening a phage .lambda.gt10 cDNA library from the human Lopez LGL leukemia with the rat RNK-Met-1 (Met-ase) cDNA clone. The Lopez cDNA phage library was constructed using the .lambda.gt10 vector and EcoRI cDNA inserts derived from human Lopez NK leukemia mRNA at the Slone Kettering Memorial Cancer Center (New York, N.Y.) by Dr. Joseph Trapani. The phage library was screened by plaque hybridization (1.times.10.sup.6) with random-primed rat RNK-Met-1 cDNA. All filter hybridizations were performed at 42.degree. C. in the presence of 5.times.SSC containing 25% formamide; the filters were washed with 2.times.SSC at 55.degree. C. The recombinant phages were plaque purified, isolated from overnight liquid cultures and phage DNA was purified, EcoRI digested and subcloned into the EcoRI site of the vector pBluescript KS.sup.+. Sequencing was performed in both orientations using synthetic oligonucleotides, the dideoxy method and single stranded and double stranded templates. The entire final sequence was determined from both strands.

Biochemical Purification of a Novel Serine Protease From the Granules of a Rat NK Leukemia.

Extracts of granules from the rat NK cells lines RNK-7 and RNK-16 have previously been reported to exhibit a number of protease activities including Tryptase, Chymase, Asp-ase, Met-ase, and Ser-ase activities when tested against a variety of synthetic substrates (Hudig, D., et al. J. Immunol. 147:1360-1368 (1991)). Whether these different enzymatic activities are due to distinct highly specific proteases or are the result of the broad substrate specificity of a more limited number of individual proteases is at present unclear. The biochemical purification to homogeneity of one of these proteases, RNKP-1, which exhibited an Asp-ase activity but appeared devoid of Met-ase activity also has been reported (Sayers, T. J., et al. J. Immunol. 148: 292-300 (1992)). A similar biochemical strategy was used herein in order to purify the Met-ase activity from the RNK granules.

The granule constituents were first fractionated on an ACA 54 column and fractions were collected and tested for Met-ase, Tryptase (BLT-esterase) and cytolysin (PFP) activities as shown in FIGS. 1A and 1B. The cytolytic activity was located in one major peak around 60-70 kDA as would be expected. BLT-esterase activity was localized in two peaks, one at 60-70 kDA overlapping the cytolysin activity and another around 25-35 kDA. The bulk of the Met-ase activity was associated with a peak which exhibited a slightly higher molecular mass than the smaller BLT-esterase, although a high degree of overlap between these two activities occurred. Some Met-ase activity was observed in fractions containing proteins of 70-80 kDa. This activity, however, was not further investigated. In an attempt to purify the lower molecular mase Met-ase activity from the BLT-esterase activity, fractions 96-108 were pooled, concentrated and subjected to heparin-agarose affinity chromatography. As seen in Table 1, the vast majority of both the Met-ase and BLT-esterase activities bound to heparin and were eluted at a salt concentration of 0.65M NaCl. Although this step resulted in a substantial purification of both the Met-ase and BLT-esterase activities, the two activities could not be discriminated from each other using this procedure and thus reverse phase HPLC chromatography was employed.

Fractionalization of HPLC chromatography using a very shallow gradient of acetonitrile (30-38%) resulted in the resolution of several protein peaks (FIG. 2). The bulk

of the Met-ase activity was associated with HPLC fraction 104 (Table 2), although activity was also detected in fractions 111-113. The BLT-esterase activity was found in fractions 49 and 56. In the chromatogram shown in FIG. 2, a clear separation of the BLT-esterase and the Asp-ase activities was not obtained since the majority of the Asp-ase activity was located in fraction 48 which also contained some BLT-esterase activity. However, the purification of the Asp-ase to complete homogeneity has been described (Sayers, T. J., et al. J. Immunol. 148: 292-300 (1992)), and one such preparation was used for enzymatic analysis in Table 2. Analysis of the enzyme activities of these HPLC purified proteins against synthetic substrates demonstrated that Asp-ase, Tryptase (BLT-esterase), and Met-ase activities could easily be distinguished from each other whereas Asp-ase and Ser-ase activities co-eluted upon HPLC chromatography (Table 2). The purified Met-ase also had some activity against synthetic peptides containing leucine or norleucine in the P1 position, but no activity against Asp-ase, Tryptase, or Chymase substrates. The purification of the Met-ase to homogeneity from the granule extract resulted in a 29 fold increase in the specific activity (Table 3).

As expected, PAGE of the granule Met-ase, Asp-ase and BLT-esterase demonstrated that the proteins had a very similar molecular mass (FIGS. 3A and 3B). Under reducing conditions the apparent molecular mass of the Met-ase was 30 kDa in comparison to 32 kDa for the Asp-ase and 25 kDa for the BLT-esterase. Interestingly, the apparent molecular mass of both the Met-ase and the BLT-esterase remained the same under nonreducing conditions whereas the Asp-ase migrated at 29 kDa. The N-terminal amino acid sequence was determined for the Met-ase protein using the Edman degradation method. One unambiguous N-terminal sequence was found and it is underlined in FIGS. 4A and 4B. This sequence was not found in the database of the NCI Biomedical

Supercomputing Center indicating that the rat Met-ase is a novel protein, which is designated RNK-Met-1.

Generation of RNK-Met-1 cDNA Probe Using the N-terminal Amino Acid Sequence Determination.

Two oligonucleotide primers were prepared to PCR amplify a RNK-Met-1 cDNA probe from RNK-16 total cellular RNA. The first of these (5'-3' primer) (SEQ ID NO:5 and SEQ ID NO:6) was a degenerate 41 mer coding for a 12 amino acid (SEQ ID NO:7) unique region in the N-terminus of the RNK-Met-1 protein. The second (3'-5' primer) (SEQ ID NO:8) was a 21 mer based on an Asp-Ser-Gly-Gly-Pro (SEQ ID NO:9) amino acid sequence around the active-site Ser that is completely conserved in the majority of reported SP proteins. This sequence is located 183-187 amino acids downstream from the N-terminus of the mature SP protein and thus if the RNK-Met-1 gene also encoded for a similar or identical stretch of amino acids, a PCR product of approximately 540 bp would be predicted. Indeed, stringent PCR amplification of total cellular RNA from rat RNK-16, yielded a single 534 bp product. No PCR products were obtained in the absence of either primer or when using total cellular RNA from rat N1S1 hepatoma cells as the template.

Nucleotide and Predicted Amino Acid Sequence RNK-Met-1 Indicate a Unique Serine-Dependent Protease.

The PCR product obtained was subcloned and used to screen a RNK-16 cDNA library to isolate a full length clone (FIGS. 4A and 4B). The insert of 867 bp contained a 774 bp open reading frame with 93 bp of 3' non coding region. The N-terminus of the mature SP protein (+1) and the TGA stop codon are indicated in FIGS. 4A and 4B. The RNK-Met-1 cDNA encodes a putative mature protein with 238 amino acids. The predicted m.w. for the unglycosylated protein is 26,014, which compared favorably with the observed m.w. on reduced and non-reduced (.about.30,000) SDS-PAGE gels (FIGS. 3A and 3B). The predicted isolectric point of RNK-Met-1 is 10.38 confirming its highly basic nature. The mature protein, as determined by amino acid sequencing, begins at +1 with the conserved sequence Ile-Ile-Gly-Gly (SEQ ID NO:10) found in activated SP. The amino acid sequence of the predicted protein demonstrates sequence similarities to previously published CTL SP (Table 4). RNK-Met-1 demonstrated approximately similar identity (<45%) with other SP from human, mouse and rat species, including granzyme (SP) A. This suggests that RNK-Met-1 is just as distinct as SP A from other SP. Up to 55.5% identity between SP and RNK-Met-1 was observed at the nucleotide level (data not shown). The three key amino acids representing the catalytic triad of serine proteases are the His at position 41, Asp at position 87 and Ser at position 184 (FIGS. 4A and 4B). The sequence Val-Leu-Thr-Ala-Ala-His-Cys (SEQ ID NO:11) around the His (position 41) and the sequence Gly-Asp-Ser-Gly-Gly-Pro (SEQ ID NO:12) around the active site Ser of SP are highly conserved. The mature RNK Met-1 protein contains 8 cysteine residues, 6 of which are conserved in all SP (positions 26, 42, 122, 153, 169, and 190). These conserved cysteines are expected to form three disulfide bonds (26-42, 122-153, 169-190) while the other two cysteines of RNK-Met-1 (position 180 and 206) may be analogous to the disulfide bond linking residues (position 191 and 220) in .alpha.-chymotrypsin which bridge the active-site serine.

RNK-Met-1 has several features which distinguish it from other known members of the SP family. The predicted first 20 amino acids of the RNK-Met-1 polypeptide chain are part of the hydrophobic SP signal peptide. However, the signal sequence is distinct from those derived according to the algorithm developed by von Heijne (von Heijne, G. Nucleic Acids Res. 14:4683-4690 (1986)).

The typical acidic SP propeptide at the amino terminus is not present in RNK-Met-1 but rather the leader peptide appears to be an exception in that it ends with a Glu residue. The combination of amino acid residues that are thought to determine the specificity of the substrate binding pocket (-6, +15, +16, +17, +28 relative to the active-site serine) are quite unique in RNK-Met-1. The

(-6) Ala.sup.178 of RNK-Met-1 is uncharged and therefore suggests a chymotrypsin-like activity. However, the Ser.sup.200 -Phe-Ser stretch (corresponding to +15 to +17) is clearly distinct from that found in any chymotrypsin-like or trypsin-like SP described thus far. Furthermore, RNK-Met-1 is the only SP known to have a Thr +28/29 residues C-terminal to the active-site serine. Two potential N-glycosylation sites Asn.sup.154 -Asn-Ser and Asn.sup.205 -Cys-Thr (Asn-X-Ser/Thr) are present, the former with no obvious counterpart amongst other known SP.

Expression of rat RNK-Met-1 mRNA.

Northern analysis detected an approximately 0.9 kb mRNA in total cellular RNA from in vitro and in vivo variants of RNK-16 (FIG. 5A). Equivalent levels of RNK-Met-1 mRNA were also detected in total cellular RNA from rat spleen cells that had been passed over nylon wool, cultured in IL-2 (1000 U/ml) and PMA (20 ng/ml) for 4 days, selected for plastic adherence and further cultured in the conditioned medium for another 2 days (classical rat A-LAK cells (Vujanovic, N. L., et al. J. Exp. Med. 167:15-29 (1988)) (FIG. 5B). By comparison, RNK-Met-1 mRNA could not be detected in total cellular RNA from unstimulated rat liver, colon, brain, spleen or thymus (FIG. 5A and B). In addition, rat splenocytes that were passed over nylon wool and cultured in media did not express detectable RNK-Met-1, nor did thymocytes cultured in IL-2 and PMA (as above). No cross reactivity of the RNK-Met-1 cDNA probe with total cellular RNA from human or murine NK, CTL and other cell lines was detected (FIG. 5A). Expression of .gamma.-actin mRNA in all the samples examined indicated that the total cellular RNA was intact.

Human Met-ase. Nucleotide sequencing of the cDNA clones reveals the Met-ase to be a unique member of the lymphocyte SP family. From the human nucleotide sequence, the amino acid sequence was deduced. The deduced human amino acid sequence has 66.4% identity with the rat amino acid sequence (See Table 5).

Despite the large number of murine SP characterized, only one gene encoding a rat counterpart (RNKP1, Asp-ase, SP B) and three genes encoding human counterparts (SP A, B and C) have been described. Hereinabove, a novel rat SP, RNK-Met-1, has been purified to homogeneity from the granules of a rat RNK-16 LGL leukemia in an enzymatically active form by a three step procedure. It was significant to maintain the enzymatic activity of RNK-Met-1 since leukocyte granules have been shown to contain SP-like proteins devoid of proteolytic activity (Wilde, C. G., et al. J. Biol. Chem. 265:2038-2041 (1990)). Three SP activities (Asp-ase, Tryptase and Met-ase) have been purified in an enzymatically active form. Previously, human and murine SP have been examined using the same set of thiobenzylester substrates used to measure RNK-Met-1 activity (Odake, S., et al. Biochemistry 30:2217-2227 (1991)). SPA hydrolyzed Arg- or Lys-containing substrates most effectively, but also hydrolyzed substrates such as Suc-Phe-Leu-Phe-SBzl and Suc-Ala-Ala-Pro-Phe-SBzl at much slower rates. SP D, E and F demonstrated minor activity toward Arg- or Lys-containing substrates and SP F also had activity toward Suc-Phe-Leu-Phe-SBzl. SP C did not hydrolyze any thioester substrate. The cloned RNK-Met-1 cDNA predicts a 238 amino acid mature protein with several structural features consistent with all SP isolated to date. The characteristic N-terminal sequence Ile-Ile-Gly-Gly (SEQ ID NO:10) was present in RNK-Met-1. In addition, the His, Asp and Ser residues that make up the active-site Ser charge relay system were found in RNK-Met-1 at homologous positions flanked by well-conserved peptide segments present in all SP family members. Six cysteine residues (of a total of 8) were conserved in homologous positions and are expected to form three internal disulfide bonds. The other two cysteine residues of RNK-Met-1 (position 180 and 206) may be analogous to the disulfide bond linking residues 191 and 220 in .alpha.-chymotrypsin, which bridge the active site serine (Le Trong, J., et al. Proc. Natl. Acad. Sci. USA 84:364-367 (1987); Le Trong, J., et al. Biochemistry 26:6988-6994 (1987)). Significantly, all of the chymotrypsin-like SP of lymphocytes described thus far lack this disulfide bond, while the trypsin like SP A has 9 cysteines including those at positions 180 and 206 (Gershenfeld, H. K., et al. Proc. Nat'l Acad. Sci. USA 85:1184-1185 (1988)).

RNK-Met-1 has other features distinguishing it from the chymotrypsin-like SP and likening it to trypsin-like SP A and kallikrein gene family (Mason, A. J., et al. Nature 303:300-307 (1983)). The signal peptides of the chymotrypsin-like SP are followed by a two- or four-residue propeptide (activation peptide) ending in a Glu (Jenne, D., et al. Proc. Natl. Acad. Sci. USA 85:4814-4818 (1988)). However the propeptides of SPA and kallikrein (mGK-1) end with a basic residue, Arg (Gershenfeld, H. K., et al. Proc. Nat'l Acad. Sci. USA 85:1184-1185 (1988); Mason, A. J., et al. Nature 303:300-307 (1983)), and the putative propeptide of RNK-Met-1 is at least 20 residues long and also ends with a basic residue, Gln. Interestingly, RNK-Met-1 also displays characteristics that differ from those documented in trypsin-like SP. The amino acid residue located (-6) positions amino-terminal to the active-site serine forms the bottom of the S.sub.1 substrate binding pocket and this determines the substrate specificity in the P.sub.1 position of a substrate (Kraut, J. Annu. Rev. Biochem. 46:331-358 (1977); Bode, W., et al. Biochemistry 28:1951-1963 (1989)). Similar to: SP D, E and H (Thr); SP B and C, Cathepsin G and rat mast cell protease (RMCP) lI (Ala); and SP F and .alpha.-chymotrypsin (Ser), the Ala.sup.178 (-6 from Ser.sup.184) of RNK-Met-1 is an uncharged residue and therefore suggests a chymotrypsin-like activity. By contrast, the trypsin-like SP A which cleaves after Lys or Arg residues contains the negatively charged Asp six residues N-terminal to its active-site serine. The low polarity of Ala.sup.178 in RNK-Met-1 indicates a preference for a hydrophobic amino acid at the P.sub.1 position in the substrate and methionine fits this description. However, residues at positions +15 to +17 and +28 relative to the active-site serine are thought to determine the specificity of the substrate binding pocket (Kraut, J. Annu. Rev. Biochem, 46:331-358 (1977); Bode, W., et al. Biochemistry 28:1951-1963 (1989)). Insertion of an additional residue between the active-site serine and this 3 amino acid stretch positions these residues +16 to +18 and +29 C terminal in RNK-Met-1. When the corresponding residues of RNK-Met-1 in these positions are compared to those of other SP, amino acid replacements are observed, suggesting distinct substrate specificity due to the altered shape and size of the substrate binding pocket. The Ser-Phe-Ser amino acid stretch in RNK-Met-1 is distinct from .alpha.-chymotrypsin (Ser-Trp-Gly) and SPA (Ser-Phe-Gly) and those SP containing a Tyr 16 positions C-terminal to the active-site serine (Ser-Try-Gln in SP B, C and H, RMCPI and II, Cathepsin G and human leukocyte protease; Ala-Tyr-Ala in SP D and E; and Thr-Tyr-Gly in SP F). RNK-Met-1 is the only SP described thus far with a Thr +28/29 residues C-terminal to the active-site serine.

The putative N-glycosylation sites Asn-Asn-Ser (positions 154-156) and Asn-Cys-Thr (positions 205-207) in RNK-Met-1 are distinct from putative N-glycosylation sites in SP B (positions 65, 98), SP H (position 65, 98, 175) and Cathepsin G (position 65). The Asn.sup.205 -Cys-Thr peptide of RNK-Met-1 is similar to one of 3, 4 and 5 sites present in SP F, E and D respectively. However, the Cys.sup.206 residue may also putatively be disulfide bonded to Cys.sup.180 and therefore the likelihood of N-glycosylation at this site might be questioned. Differences in glycosylation may influence the specificity of substrate binding (Salvensen, G., et al. Biochemistry 26:2289-2293 (1987)) and may result in functional heterogeneity when this site is not constantly used for glycosylation. Additionally, the amount of negatively charged N-linked carbohydrate influences the net charge of the SP and may affect the affinity for proteoglycans and their dissociation rates after secretion. The presence and functional role of N-glycosylation in RNK-Met-1 remain to be determined.

Clearly, RNK-Met-1 is expressed in activated rat A-LAK splenocytes. Whether RNK-Met-1 is also expressed in non-cytolytic cells and non-lymphoid lineages is not known. Although, RNK-Met-1 has only been detected in rat LGL, Met-ase activities have been described for granule preparations from human CTL and murine NK cells (Odake, S., et al. Biochemistry 30:2217-2227 (1991); T. J. Sayers, unpublished data). Homologous mRNAs were not detected in human LGL- or murine CTL-cell lines by Northern analysis. However, Southern analysis of human and murine genomic DNA would suggest that RNK-Met-1- like genes do exist in these species (data not shown). Evidently, with few exceptions, murine SP gene expression is restricted to T cells and their thymic precursors and NK cells (Garcia-Sanz, J. A., et al. J. Immunol. 145:3111-3118 (1990)).

All publications mentioned hereinabove are hereby incorporated by reference in their entirety.

While the foregoing invention has been described in some detail for purposes of clarity and understanding, it will be appreciated by one skilled in the art from a reading of the disclosure that various changes in form and detail can be made without departing from the true scope of the invention in the appended claims.