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The molecular chaperone Hsp90 is distinct from Hsp70 and chaperonin in that client proteins are apparently restricted to a subset of proteins categor-ized as cellular signaling molecules. Among these, many specific protein kinases require the assistance of Hsp90 and its co-chaperone Cdc37⁄p50 for their biogenesis. A series of Cdc37 deletion mutants revealed that all mutants capable of binding Raf-1 possess amino acid residues between 181 and 200. | iFEBS Journal A client-binding site of Cdc37 Kazuya Terasawa and Yasufumi Minami Department of Biophysics and Biochemistry and Undergraduate Program for Bioinformatics and Systems Biology Graduate Schoolof Science University of Tokyo Japan Keywords Cdc37 Hsp90 protein kinase Raf-1 Correspondence Y. Minami Department of Biophysics and Biochemistry and Undergraduate Program for Bioinformatics and Systems Biology Graduate Schoolof Science The University of Tokyo Hongo 7-3-1 Bunkyo-ku Tokyo 113-0033 Japan Fax 81 3 5841 3047 Tel 81 3 5841 3047 E-mail yminami@biochem.s.u-tokyo.ac.jp Received 28 June 2005 revised 23 July 2005 accepted 26 July 2005 doi 10.1111 j.1742-4658.2005.04884.x The molecular chaperone Hsp90 is distinct from Hsp70 and chaperonin in that client proteins are apparently restricted to a subset of proteins categorized as cellular signaling molecules. Among these many specific protein kinases require the assistance of Hsp90 and its co-chaperone Cdc37 p50 for their biogenesis. A series of Cdc37 deletion mutants revealed that all mutants capable of binding Raf-1 possess amino acid residues between 181 and 200. The 20-residue region is sufficient and in particular a five-residue segment residue 191-195 is essential for binding to Raf-1. These five residues are present in one a helix residues 184-199 in the middle of Cdc37 which is unexpectedly nested within the Hsp90-interacting domain of Cdc37 which was recently determined by crystallography but does not seem to contribute to direct contact with Hsp90. Furthermore an N-ter-minally truncated mutant of Cdc37 composed of residues 181-378 was shown to bind the N-terminal portion of Raf-1 subdomains I-IV . This mutant can bind not only other Hsp90 client protein kinases Akt1 Aurora B and Cdk4 but also Cdc2 and Cdk2 which to date have not been shown to physically interact with Cdc37. These results suggest that a region of Cdc37 other than the client-binding site may be responsible for discriminating client protein
