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Structure, Mechanism Of Cell-Signaling Interaction Revealed
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U.S. and British scientists have obtained the structure of the complex that forms ou're looking even under stringent when a key cell-signaling protein domain at a pump conditions. With almost binds to its phosphopeptide target And that no no maintenance. they've studied the chemical and mechacompetitor ca Plus, you don't have nistic basis for the cellular signals propatouch. The variable spee gated by such interactions. to worry about fitting your The study focused on forkhead-as- precision metering pump application to the pump. We sociated (FHA) domains, peptide se- from Eldex. offer a variety of models-includquences of about 120 amino acids each. ing metal-free-with flow rates from NOTHING TO HANDLE FHA domains are found in transcription 0.025 to 40 mL/min., at pressures You don't have to waste time turning factors and other types of cell-signaling up to 5,000 psi. You'll get the best it on or off or making flow adjustproteins in a wide variety of organisms, pump for your application. ments by hand. Your computer can ranging from bacteria to humans. handle all that by remote control. AT AN UNMATCHED PRICE Functionally, these domains are beTo order or learn more, give us lieved to play a role in the repair of damNOTHING TO aged DNA, and several human cancers a call. WORRY ABOUT are associated with loss of FHA-contain- You don't have to worry about Tel: 1-800-969-3533 ing proteins or with mutations in FHA do- replacing a DC-brush motor in the Fax: 1-707-224-0688 mains. Although the domains are known to bind to peptides and cellular proteins middle of a project. Our VS pumps containing phosphorylated threonine res- come with an AC Sync motor to idues, the underlying chemistry and de- accurately meter fluids for yearstailed mechanism of such interactions © Eldex Laboratories, Inc. 1991 CIRCLE 30 ON READER SERVICE CARD have not been known. Now, the X-ray crystal structure of a phosphopeptide complex of an FHA domain has been solved, revealing important clues about the domains' functional mechanism. The work was a collaborative effort by assistant professor of biology Michael B. Yaffe of Massachusetts Institute of Technology and Harvard Medi& * cal School; professor Stephen J. Smerdon of the Division of Protein Structure at the National Institute for Medical Research, London; biology professor Stephen P. Jackson at the University of Cambridge; and coworkers [Mol. Cell, 6,1169 (2000)1. They used combinatorial peptide library techniques to decode specific sequences that different FHA domains bind to, and then solved the structure of an & Ar B + Ar X Ar-Ar FHA domain bound to a phosphopeptide. The crystal structure is that of a complex between the FHA domain of Rad53p— a protein associated with DNA damage repair—and a phosphothreonine-contain• Improved Yields • Higher Purity ing peptide from Rad9p, a protein Rad53p • Greater Cost Efficiency binds to in cells. Thefindingscould lead to a better understanding of phosphopep^ ^ A n d e r s o n tide-mediated signaling in general and to - = ^ = . D K V B L . O P M K I M T C O M P A N Y the mechanisms of FHA domain-related tumor suppression and DNA damage sigA SPECIALTY CHEMICAL COMPANY naling in particular. E-mail:
[email protected] • www.andersondevelopment.com A number of protein domains—of 1415 E. Michigan Street • Adrian, Ml 49221-3499 • U.SA • (517) 263-2121 • FAX (517) 263-1000 which SH2 (Src homology 2) domains
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science/technology Asked to comment on the study, Tomi Sawyer, vice president of drug discovery at Ariad Pharmaceuticals, Cambridge, Mass., says it is relevant "to our developing understanding of phosphoprotein molecular recognition, which underlies complex biological processes, including signal transduction pathways critical to DNA repair and transcriptional regulation." Earlier this year, Sawyer and coworkers at Ariad discovered the first in vivo inhibitor of SH2—or of any other cell-signaling protein domain, for that matter [Proc. Natl. Acad. Sci. USA, 9 7 , 9373 (2000); C&EN, Aug. 28, page 34]. What is striking in the new study, Sawyer says, "is that the mode of binding between the FHA domain and a cognate phoshothreonine-containing peptide is unique relative to other known protein domains that interact with phosphopeptides. Without question, the Xray structure of the FHA domain complexed with a phosphothreonine-containing peptide answers all mysteries and, more importantly, provides intriguing clues to die roles of this newly defined domain in biological processes." The FHA domain complex, "now structurally determined, adds to a short list of extraordinary protein-protein interactions that nature utiComplex off FHA domain with lizes in the regulation of signal transduction processes in cellular target phosphopeptide function," Sawyer adds. "It would not be surprising that drug discovery efforts on FHA domains might be feasible given that success has been achieved in the case of SH2 domain-targeted peptidomimetic and de novo designed nonpeptides that show in vitro and in vivo efficacy." Yaffe tells C&EN that he and his coworkers currently are moving in several new directions. "We are using bioinformatics techniques to search the human proteome for proteins predicted Structure of complex to bind to FHA domains whose obtained by optimal sequence motifs we deYaffe, Smerdon, Jackson, duced from combinatorial pepand coworkers reveals tide libraries." In addition, he binding interactions (dashsays, "we are working on solving es) between arginme residues (green baflthe structures of several additionand-stick models) in the FHA domain and phosphothreonine and aspartate residues al FHA domain-peptide complexon me phosphopeptide (pink ball-and-stick es, and we are trying to undermodel at top). Peptide residues on either stand how binding of Rad9p to side of the central phosphothreonine make the FHA domains in Rad53p concritical contributions to the selectivity of trols signaling events in response different phosphopeptide-FHA domain to DNA damage." interactions. Stu Borman
are perhaps the best known—play crucial roles in cell-signaling processes and have therefore been undergoing intensive research scrutiny since their discovery in the mid-1980s. Many of these domains, including SH2, bind to phosphorylated tyrosine sites in their protein targets. But FHA domains bind instead to phosphorylated threonine sites. FHA domains have been considered to be of secondary importance as cellsignaling domains up to now, largely because the way in which they interact with their binding partners has not been well understood. The study by Yaffe, Smerdon, Jackson, and coworkers could therefore help focus greater attention on FHA domains as potential pharmaceutical research targets. The researchers demonstrate that the selectivity of FHA domain binding to phosphopeptide sites is determined by short sequence motifs that flank both sides of phosphorylated threonine residues in protein binding sites. FHA domains thus use both a common feature (the presence of a phosphothreonine residue) and a divergent feature (the type of amino acids arrayed on either side of that residue) to recognize specific phosphorylated binding sites.
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