US 5,776,696 AGrant
High Throughput Assay Using Fusion Proteins
Issue Date:1998-07-07
•10 Claims
•1 Drawing Sheets
Abstract
This application describes a high throughput assay for screening for compounds which are capable of binding to a fusion protein which consists of a target protein and an FKS506-binding protein.
Metadata
Assignee
- Merck & Co., Inc.
Inventor
- Scott P. Salowe
Application Information
Application Number:US 7077939
Filing Date:1996-09-04
Priority Date:1996-09-04
Art Unit:182
Classifications
IPC:
G01N 3353G01N 33546G01N 33566G01N 3360G01N 3368
Field of Search:
4355305369307.1;7.5;7.72;7.8;969;973324;344;350;872;876;82723.4280
Patent Drawings (1 sheets)
Description
Domestic Priority Claim
The priority of U.S. Provisional application Ser. No. 60/003,824, filed on Sep. 15, 1995, now abandoned, is claimed.
Background of the Invention
Src homology 2 (SH2) domains are a family of homologous protein domains that share the common property of recognizing phosphorylated tyrosine residues in specific peptide contexts. They have routinely been expressed in E. coli as fusion proteins with glutathione-S-transferase (GST). This usually provides high level expression and straightforward affinity purification on glutathione-Sepharose. Ligand binding is then assayed by incubating the GST/SH2 with a radiolabeled phosphopeptide, precipitating the complex with glutathione-Sepharose, washing the beads, and then counting the beads to determine bound radioactivity Isakov et al., J. Exp. Med., 181, 375-380 (1995); Piccione et al., Biochemistry, 32, 3197-3202 (1993); Huyer et al., Biochemistry, 34, 1040-1049 (1995)!. There are several disadvantages to this procedure, particularly when applied to high-throughput screening for agonists, antagonists, or inhibitors as new leads for drug development. First, the radiolabeling of the peptide is carried out either enzymatically with a kinase and .sup.32 P!ATP or chemically with .sup.125 I!Bolton-Hunter reagent. In both cases, the isotopes are short-lived and thus require frequent preparation of material. In the case of enzymatic phosphorylation, the appropriate kinase must also be available in sufficient quantity to generate enough material for screening purposes. Second, the protocol requires separation of bound complex from free phosphopeptide by washing of the glutathione-Sepharose beads. This is a nonequilibrium procedure that risks dissociation of the bound ligand, particularly when off-rates are fast. Thus, there is the possibility of misleading results. Finally, due to the number of manipulations and centrifugations involved, the protocol is very tedious to conduct manually and is not readily adaptable to robotic automation to increase throughput.
Two additional methods for measuring the interaction of proteins and ligands that have been applied to SH2 domains are biospecific interaction analysis using surface plasmon resonance and isothermal titration calorimetry (Felder et al., Mol. Cell. Biol., 13, 1449-1455 (1993); Panayotou et al., Mol. Cell. Biol., 13, 3567-3576 (1993); Payne et al., Proc. Natl. Acad. Sci. U.S.A., 90, 4902-4906 (1993); Morelock et al., J. Med. Chem. 38, 1309-18 (1995); Ladbury et al., Proc. Natl. Acad. Sci. U.S.A., 92, 3199-3203 (1995); Lemmon et al., Biochemistry, 33, 5070-5076 (1994)). These techniques do not require a particular fusion partner for the SH2 domain, but do require sophisticated instrumentation that is not amenable to high throughput screening.
Summary of the Invention
The instant invention covers a method of screening for compounds capable of binding to a fusion protein which comprises combining a test compound, a tagged ligand, a fusion protein (target protein, peptide linker and FK506-binding protein), a radiolabeled ligand, and coated scintillation proximity assay (SPA) beads, and then measuring the scintillation counts attributable to the binding of the tagged ligand to the fusion protein in the presence of the test compound relative to a control assay in the absence of the test compound, so as to determine the effect the test compound has on the binding of the tagged ligand. This invention provides an immediate means of making use of SPA technology for the functional assay of ligand binding to a single or multiple signal transduction domain(s), for example a phosphopeptide binding to an SH2 domain. The present invention does not require specialized radiochemical synthesis and is readily adaptable to robotic automation for high capacity screening for agonists, antagonists, and/or inhibitors.
Brief Description of the Figures
FIG. 1.
A.) Binding of the streptavidin SPA bead, biotinylated ligand and the fusion protein (SH2:FKBP), which emits a detectable signal; and
B.) Binding of the test compound and the fusion protein (SH2:FKBP), which results in no signal detection.
Detailed Description of the Invention
The present invention relates to a method of screening for compounds which preferentially bind to a target protein.
An embodiment of this invention is a method of screening for compounds capable of binding to a fusion protein which comprises the steps of:
a) mixing a test compound, a tagged ligand, the fusion protein, a radiolabeled ligand and coated scintillation proximity assay (SPA) beads;
b) incubating the mixture for between about 1 hour and about 24 hours;
c) measuring the SPA bead-bound counts attributable to the binding of the tagged ligand to the fusion protein in the presence of the test compound using scintillation counting; and
d) determining the binding of the tagged ligand to the fusion protein in the presence of the test compound relative to a control assay run in the absence of the test compound.
The term "fusion protein" refers to a "target protein" fused to an "FK506-binding protein" (FKBP), the two proteins being separated by a "peptide linker".
A "peptide linker" may consist of a sequence containing from about 1 to about 20 amino acids, which may or may not include the sequence for a protease cleavage site. An example of a peptide linker which is a protease cleavage site is represented by the amino acid sequence GLUPRGS (SEQ.ID.NO: 7).
The term "target protein" refers to any protein that has a defined ligand. Included within this definition of target protein are single and multiple signal transduction domains, such as, but not limited to, Src homology 1 (SH1), Src homology 2 (SH2), Src homology 3 (SH3), and pleckstrin homology (PH) domains Hanks & Hunter, FASEB J., 9, 576-596 (1995); Bolen, Curr. Opin. Immunol., 7, 306-311 (1995); Kuriyan & Cowbum, Curr. Opin. Struct. Biol., 3, 828-837 (1993); Cohen et al., Cell, 80, 237-248 (1995)!. The term "SH1 domain" refers to a family of homologous protein domains that bind ATP and catalyze tyrosine phosphorylation of peptide and protein substrates. The term "SH2 domain" refers to a family of homologous protein domains that share the common property of recognizing phosphorylated tyrosine residues in specific peptide contexts. The term "SH3 domain" refers to a family of homologous protein domains that share the common property of recognizing polyproline type II helices. The term "PH domain" refers to a family of homologous protein domains that mediate both protein-protein and protein-lipid interactions. Examples of SH2 domains which may be utilized in the method of the invention include, but are not limited to, the single and tandem SH2 domains present in the tyrosine kinases ZAP, SYK and LCK. The DNA sequences were obtained from GenBank, National Center for Biotechnology Information, National Library of Medicine, 8600 Rockville Pike, Bethesda, Md. 20894. The Accession Numbers for the sequences are: human ZAP (LO5148); human SYK (L28824) and human LCK (X13529). The sequences for ZAP, Syk and Lck are disclosed in the sequence listing as follows: the isolated DNA encoding for a fusion protein containing ZAP is (SEQ.ID.NO. 1); the isolated DNA encoding for a fusion protein containing Syk is (SEQ.ID.NO. 2); the isolated DNA encoding for a fusion protein containing Lck is (SEQ.ID.NO. 3); the sequence for the FKBP-ZAP:SH2 fusion protein is (SEQ.ID.NO. 4); the sequence for the FKBP-Syk:SH2 fusion protein is (SEQ.ID.NO. 5); and the sequence for the FKBP-Lck:SH2 fusion protein is (SEQ.ID.NO. 6).
The term "tagged ligand" refers to a biotinylated or epitope tagged ligand for the target protein.
The term "radiolabeled ligand" refers to a .sup.3 H!- or .sup.125 I!-labeled ligand which binds to the FKBP. An example of a radiolabeled ligand useful in the instant invention is .sup.3 H!-dihydroFK506.
The term "coated scintillation proximity assay beads" (SPA beads) refers to streptavidin-coated scintillation proximity assay beads when the tagged ligand is biotinylated, and to anti-epitope antibody bound to anti-antibody-coated or protein A-coated scintillation proximity assay beads when the tagged ligand is epitope-tagged.
The term "control assay" refers to the assay when performed in the presence of the tagged ligand, the fusion protein, the radiolabeled ligand and the coated scintillation proximity assay beads, but in the absence of the test compound.
The term FK506-binding proteins may include, but are not limited to, the below listed FKBPs and FKBP homologues, which include a citation to the references which disclose them. This list is not intended to limit the scope of the invention.
A variety of host cells may be used in this invention, which include, but are not limited to, bacteria, yeast, bluegreen algae, plant cells, insect cells and animal cells.
Expression vectors are defined herein as DNA sequences that are required for the transcription of cloned copies of genes and the translation of their mRNAs in an appropriate host. Such vectors can be used to express genes in a variety of host cells, such as, bacteria, yeast, bluegreen algae, plant cells, insect cells and animal cells.
Specifically designed vectors allow the shuttling of DNA between hosts such as bacteria-yeast or bacteria-animal cells. An appropriately constructed expression vector may contain: an origin of replication for autonomous replication in host cells, selectable markers, a limited number of useful restriction enzyme sites, a potential for high copy number, and active promoters. A promoter is defined as a DNA sequence that directs RNA polymerase to bind to DNA and initiate RNA synthesis. A strong promoter is one which causes mRNAs to be initiated at high frequency. Expression vectors may include, but are not limited to, cloning vectors, modified cloning vectors, specifically designed plasmids or viruses. Commercially available vectors suitable for FKBP fusion protein expression include, but are not limited to pBR322 (Promega), pGEX (Amersham), pT7 (USB), pET (Novagen), pIBI (IBI), pProEX-1 (Gibco/BRL), pBluescript II (Stratagene), pTZ18R and pTZ19R (USB), pSE420 (Invitrogen), pVL1392 (Invitrogen), pBlueBac (Invitrogen), pBAcPAK (Clontech), pHIL (Invitrogen), pYES2 (Invitrogen), pCDNA (Invitrogen), pREP (Invitrogen) or the like.
The expression vector may be introduced into host cells via any one of a number of techinques including but not limited to transformation, transfection, infection, protoplast fusion, and electroporation.
E. coli containing an expression plasmid with the target gene fused to FKBP are grown and appropriately induced. The cells are then pelleted and resuspended in a suitable buffer. Although FKBP-12 lacks sequences that specifically direct it to the periplasm, FKBP fusions are primarily located there and can be released by a standard freeze/thaw treatment of the cell pellet. Following centrifugation, the resulting supernatant contains >80% pure FKBP fusion, which if desired can be purified further by conventional methods. Alternatively, the assay is not dependent on pure protein and the initial periplasmic preparation may be used directly. A thrombin site located between FKBP and the target protein can be used as a means to cleave FKBP from the fusion; such cleaved material may be a suitable negative control for subsequent assays.
A fusion protein which contains a single or multiple SH2 domain(s) may be purified by preparing an affinity matrix consisting of biotinylated phosphopeptide coupled to avidin or streptavidin immobilized on a solid support. A freeze/thaw extract is prepared from the cells which express the fusion protein and is loaded onto the affinity matrix. The desired fusion protein is then specifically eluted with phenyl phosphate.
To assay the formation of a complex between a target protein and its ligand, the tagged ligand is mixed with the FKBP fusion protein in a suitable buffer in the presence of the radiolabeled ligand in the well of a white microplate. After a suitable incubation period to allow complex formation to occur, coated SPA beads are added to capture the tagged ligand and any bound fusion protein. The plate is sealed, incubated for a sufficient period to allow the capture to go to completion, then counted in a multiwell scintillation counter. Screening for agonists/antagonists/inhibitors is carried out by performing the initial incubation prior to the capture step with SPA beads in the presence of a test compound(s) to determine whether they have an effect upon the binding of the tagged ligand to the fusion protein. This principle is illustrated by FIG. 1.
The present invention can be understood further by the following examples, which do not constitute a limitation of the invention.
Example 1
Process for Preparing the FKBP fusion cloning vector
General techniques for modifying and expressing genes in various host cells can be found in Ausubel, F. M., Brent, R., Kingston, R. E., Moore, D. D., Seidman, J. G., Smith, J. A. and Struhl, K. Current Protocols in Molecular Biology (John Wiley & Sons, New York, N.Y., 1989). Sequences for a 3'-altered FKBP fragment that contained a glycine codon (GGT) in place of the stop (TGA) codon followed by a sequence encoding a thrombin site (Leu-Val-Pro-Arg) and BamHI restriction site (GAATTC) were amplified using the polymerase chain reaction (PCR). The PCR reaction contained the following primers: 5'-GATCGCCATGGGAGTGCAGGTGGAAACCATCTCCCCA-3' (SEQ.ID.NO. 8) and 5'-TACGAATTCTGGCGTGGATCCACGCGGAACCAGACCTTCCAGT TTTAG-3' (SEQ.ID.NO. 9) and a plasmid containing human FKBP-12 as the template. The resulting 367 base pair amplification product was ligated into the vector pCRII (Invitrogen) and the ligation mixture transformed into competent Escherichia coli cells. Clones containing an insert were identified using PCR with flanking vector primers. Dideoxy DNA sequencing confirmed the nucleotide sequence of one positive isolate. The altered 338 base pair FKBP fragment was excised from the pCRII plasmid using NcoI and BamHI and ligated into NcoI and BamHI digested pET9d (Novagen) plasmid. Competent E. coli were transformed with the ligation mixture, and colonies containing the insert were identified using PCR with primers encoding for flanking vector sequences. The FKBP fusion cloning vector is called pET9dFKBPt.
Example 2
Process for Preparing the FK-ZAP fusion expression vector
A DNA fragment encoding for the tandem SH2 domains of ZAP-70 was prepared by PCR to contain a BamHI site at the 5'-end such that the reading frame was conserved with that of FKBP in the fusion vector. At the 3'-end, the fragment also incorporated a stop codon followed by a BamHI site. The PCR reaction contained Molt-4 cDNA (Clontech) and the following primers: 5'-ATTAGGATCCATGCCAGATCCTGCAGCTCACCTGCCCT-3' (SEQ.ID.NO. 10) and 5'-ATATGGATCCTTACCAGAGGCGTTGCT-3' (SEQ.ID.NO. 11). The fragment was cloned into a suitable vector, sequenced, digested with BamHI, and the insert containing the SH2 domains ligated to BamHI treated pET9dFKBPt, and transformed into E. coli. Clones containing inserts in the correct orientation were identified by PCR or restriction enzyme analysis. Plasmid DNA was prepared and used to transform BL21(DE3) cells.
Example 3
Process for Preparing the FK-SYK fusion expression vector
The expression vector for the tandem SH2 domains of Syk fused to FKBP was prepared as in Example 2 except that the PCR reaction contained Raji cell cDNA (Clontech) and the following primers: 5'-CAATAGGATCCATGGCCAGCAGCGGCATGGCTGA-3' (SEQ.ID.NO. 12) and 5'-GACCTAGGATCCCTAATTAACATTTCCCTGTGTGCCGAT-3' (SEQ.ID.NO. 13).
Example 4
Process for Preparing the FK-LCK fusion expression vector
The expression vector for the SH2 domain of Lck fused to FKBP was prepared as in Example 2 except that the PCR reaction contained Molt-4 cDNA (Clontech) and the following primers: 5'-ATATGGATCCATGGCGAACAGCCTGGAGCCCGAACCCT-3' (SEQ.ID.NO. 14) and 5'-ATTAGGATCCTTAGGTCTGGCAGGGGCGGCTCAACCGTGT GCA-3' (SEQ.ID.NO. 15).
Example 5
FK-ZAP
Step A: Process for Expression of FK-ZAP
E. coli BL21(DE3) cells containing the pET9dFKBPt/ZapSH2 plasmid were grown in Luria-Bertani (LB) media containing 50 microgram/ml kanamycin at 37 degrees C. until the optical density measured at 600 nm was 0.5-1.0. Expression of the FK-ZAP fusion protein was induced with 0.1 mM isopropyl beta-thiogalactopyranoside and the cells were grown for another 3-5 hr at 30 degrees C. They were pelleted at 4400.times.g for 10 min at 4 degrees C. and resuspended in 2% of the original culture volume with 100 mM tris pH 8.0 containing 1 microgram/ml each aprotinin, pepstatin, leupeptin, and bestatin. The resuspended pellet was frozen at -20 degrees C. until further purification.
Step B: Process for Purification of FK-ZAP
The affinity matrix for purification of FK-ZAP was prepared by combining agarose-immobilized avidin with excess biotinylated phosphopeptide derived from the .zeta.1 ITAM sequence of the human T-cell receptor, biotinyl-GSNQLpYNELNLGRREEpYDVLDK (SEQ.ID.NO. 16), and washing out unbound peptide. Frozen cells containing FK-ZAP were thawed in warm water, refrozen on dry ice for about 25 min., then thawed again. After the addition of 0.1% octyl glucoside, 1 mM dithiothreitol (DTT) and 500 mM NaCl, the extract was centrifuged at 35,000.times.g for approximately 30 minutes. The supernatant was loaded onto the phosphopeptide affinity column, at about 4.degree. and washed with phosphate buffered saline containing 1 mM DTT and 0.1% octyl glucoside. FK-ZAP was eluted with 200 mM phenyl phosphate in the same buffer at about 37.degree.. The protein pool was concentrated and the phenyl phosphate removed on a desalting column. The purified FK-ZAP was stored at about -30.degree. in 10 mM HEPES/150 mM NaCl/1 mM DTT/0.1 mM EDTA/10% glycerol.
Example 6
FK-SYK
E. coli BL21(DE3) cells containing the pET9dFKBPt/SykSH2 plasmid were grown, induced, and harvested as described in Example 5. FK-SYK was purified using the same affinity matrix and methodology described in Example 5.
Example 7
FK-LCK
E. coli BL21(DE3) cells containing the pET9dFKBPt/LckSH2 plasmid were grown, induced, and harvested as described in Example 5. The affinity matrix for purification of FK-LCK was prepared by combining agarose-immobilized avidin with excess biotinyl-EPQpYEEIPIYL, and washing out unbound peptide. The remaining methodology for purification was the same as Example 5.
Example 8
Method of Screening for Antagonists of FK-ZAP
Assays were conducted at ambient temperature in a buffer consisting of 25 mM HEPES, 10 mM DTT, 0.01% TWEEN-20, pH 7.0. 10 .mu.l of a DMSO solution of test compound(s) and 120 .mu.l of biotinyl-phosphopeptide stock solution were dispensed into the wells of a 96-well Packard Optiplate. Next, 20 .mu.l of a mixture of FK-ZAP protein and .sup.3 H-dihydroFK506 were added to each test well. Finally, 50 .mu.l of a 4 mg/ml suspension of SPA beads were dispensed to each well. Final concentrations of the assay components were:
25 nM biotinyl-GSNQLpYNELNLGRREEpYDVLDK (SEQ.ID.NO. 16)
25 nM FK-ZAP fusion protein
10 nM .sup.3 H-dihydroFK506 (DuPont NEN)
1.0 mg/ml streptavidin-SPA beads (Amersham)
5% DMSO
The plate was sealed and incubated between 1 and 8 hours. Bead-bound radioactivity was then measured in a Packard Topcount microplate scintillation counter.
Example 9
Method of Screening for Antagonists of FK-SYK
The assays were conducted as set forth in Example 8, except that FK-SYK replaced FK-ZAP.
Example 10
Method of Screening for Antagonists of FK-LCK
The assays were conducted as set forth in Example 8, except that FK-LCK replaced FK-ZAP and the tagged ligand was 25 nM biotinyl-EPQpYEEIPIYL (SEQ.ID.NO. 17).
Claims
What is claimed is:
1. A method of screening for compounds capable of binding to a fusion protein, which is defined as an FK506-binding protein linked to a target protein through a peptide linker, which comprises the steps of: a) mixing a test compound, a tagged ligand for the target protein, which is selected from a biotinylated ligand or an epitope-tagged ligand, the fusion protein, a radiolabeled ligand selected from .sup.3 H!- or .sup.125 I!-labeled FK506 analog and coated scintillation proximity assay (SPA) beads selected from streptavidin-coated or anti-antibody coated or protein A-coated beads; b) incubating the mixture from between about 1 hour to about 24 hours; c) measuring the SPA bead-bound counts attributable to the binding of the tagged ligand to the fusion protein in the presence of the test compound using scintillation counting; and d) determining the binding of the tagged ligand to the fusion protein in the presence of the test compound relative to a control assay run in the absence of the test compound.
2. The method of screening for compounds capable of binding to a fusion protein, as recited in claim 1, wherein the target protein comprises a single or multiple signal transduction domain.
3. The method of screening for compounds capable of binding to a fusion protein, as recited in claim 2, wherein the single or multiple signal transduction domain is selected from the group consisting of: SH1, SH2, SH3 and PH domains.
4. The method of screening for compounds capable of binding to a fusion protein, as recited in claim 3, wherein the target protein is a single or multiple SH2 domain.
5. The method of screening for compounds capable of binding to a fusion protein, as recited in claim 4, wherein the radiolabeled ligand is .sup.3 H!-dihydroFK506.
6. The method of screening for compounds capable of binding to a fusion protein, as recited in claim 5, wherein the FK506-binding protein is a 12 kDA human FK506-binding protein.
7. The method of screening for compounds capable of binding to a fusion protein, as recited in claim 6, wherein the target protein is a single or multiple SH2 domain selected from the group consisting of: ZAP:SH2, SYK:SH2 and LCK:SH2.
8. The method of screening for compounds capable of binding to a fusion protein, as recited in claim 7, wherein the target protein is the SH2 domain, ZAP:SH2.
9. The method of screening for compounds capable of binding to a fusion protein, as recited in claim 7, wherein the target protein is the SH2 domain, SYK:SH2.
10. The method of screening for compounds capable of binding to a fusion protein, as recited in claim 7, wherein the target protein is the SH2 domain, LCK:SH2.
Patent Citations (3)
Non-Patent Literature (17)
- Edalji et al. High-level expression of recombinant human FK-binding protein from a fusion precursor. Journal of Protein Chemistry. vol. 11, No. 3, pp. 213-223, 1992.
- Gilmer et al. Peptide inhibitors of src SH3-SH2-phosphoprotein interactions. The Journal of Biological Chemistry. vol. 269, No. 50, pp. 31711-31719, Dec. 16, 1994.
- Jin et al. The 25-kDa FK506-binding protein is localized in the nucleus and associates with casein kinase II and nucleolin. Proceedings of the National Academy of Sciences, USA, vol. 90, pp. 7769-7773, Aug. 1993.
- Muller et al. Rapid identification of phosphopeptide ligands for SH2 domains: screening of peptide libraries by fluorescence-activated bead sorting. The Journal of Biological Chemistry. vol. 271, No. 28, pp. 16500-16505, Jul. 12, 1996.
- Sampson et al. Neisseria meningitidis encodes an FK506-inhibitable rotamase. Proceedings of the National Academy of Sciences, USA. vol. 89, pp. 1164-1168, Feb. 1992.
- Lerner, et al., "Scintillation Proximity Assay for Human DNA Topoisomerase I Using Recombinant Biotinyl-Fusion Protein Produced in Baculovirus-Infected Insect Cells", Anal. Biochem., vol. 240, pp. 289-297 (1996).
- Skinner, et al., "Direct Measurment ofthe Binding of RAS to Neurofibromin Using a Scintillation Proximity Assay", Anal. Biochem., vol. 233, pp. 259-265, (1994).
- Lemmon, et al., "Thermodynamic Studies of Tyrosyl-Phosphopeptide Binding to the SH2 Domain of p56Ick", Biochemistry, vol. 33, pp. 5070-5076, 1994.
- Payne, et al., "Kinetics of p56Ick and p60src Homology 2 Domain Binding to Tyrosine-Phosphorylated Peptides Determined by a Competition Assay or Surface Plasmon Resonance", Proc. Natl. Acad. Sci. USA, vol. 90, pp. 4902-4906, 1993.
- Isakov, et al., ZAP-70 Binding Specificity to T Cell Receptor Tyrosine-Based Activation Motifs: The Tandem SH2 Domains of ZAP-70 Bind District Tyrosine-Based Activation Motifs with Varying Affinity, J. Exp. Med., vol. 181, pp. 375-380, 1995.
- Huyer, et al., "Direct Determination of the Sequence Recognition Requirements of the SH2 Domains of SH-PTP2", Biochemistry, vol. 34, pp. 1040-1049, 1995.
- Panayotou, et al., "Interactions Between SH2 Domains and Tyrosine-Phosphorylated Platelet-Derived Growth Factor Beta-Receptor Sequences: Analysis of Kinetic Parameters by a Novel Biosenor-Based Approach", Mol. Cell. Biol., vol. 13, pp. 3567-3576, 1993.
- Felder, et al., "SH2 Domains Exhibit High-Affinity Binding to Tyrosine-Phosphorylated Peptides Yet Also Exhibit Rapid Dissociation and Exchange", Mol. Cell. Biol., vol. 13, pp. 1449-1455, 1993.
- Morelock, et al., "Determination of Receptor-Ligand Kinetic and Equilibrium Binding Constants Using Surface Plasmon Resonance: Application to the Ick SH2 Domain and Phosphotyrosyl Peptides", J. Med. Chem., vol. 38, pp. 1309-1318, 1995.
- Ladbury, et al., "Measurement of the Binding of Tyrosyl Phosphopeptides to SH2 Domains: A Reappraisal", Proc. Natl. Acad. Sci. USA, vol. 92, pp. 3199-323, 1995.
- Piccione, et al., "Phosphatidylinositol 3-Kinase p85 SH2 Domain Specificity Defined by Direct Phosphopeptide/SH2 Domain Binding", Biochemistry, vol. 32(13), pp. 3197-3202, 1993.
- Sonatore, et al., "The Utility of FK506-Binding Protein as a Fusion Partner in Scintillation Proximity Assays: Appliction to SH2 Domains", Anal. Biochemistry, vol. 240, pp. 289-297, 1996.