SPECIFIC BINDING OF TETRATRICOPEPTIDE REPEAT PROTEINS TO THE C-TERMINAL 12-KDA DOMAIN OF HSP90

The molecular chaperone hsp90 in the eukaryotic cytosol interacts with a variety of protein cofactors, Several of these cofactors have prote in domains containing tetratricopeptide repeat (TPR) motifs, which med iate binding to hsp90. Using a yeast two-hybrid screen, the 12-kDa C-t erminal domain of human hspg90 alpha (C90) was found to mediate the in teraction of hsp90 with TPR-containing sequences from the hsp90 cofact ors FKBP51/54 and FKBP52. In addition, the mitochondrial outer membran e protein hTOM34p was identified as a TPR-containing putative partner protein of hsp90, In experiments with purified proteins, the TPR-conta ining cofactor p60 (Hop) was shown to form stable complexes with hsp90 . A deletion mutant of hsp90 lacking the C90 domain was unable to bind p60, whereas deletion of the similar to 25-kDa N-terminal domain of h sp90 did not affect complex formation. Both p60 and FKBP52 bound speci fically to the C90 domain fused to glutathione S-transferase and compe ted with each other for binding. In reticulocyte lysate, the C90 fusio n protein recognized the TPR proteins p60, FKBP52, and Cyp40. Thus, ou r results identify the C90 domain as the specific binding site for a s et of hsp90 cofactors having TPR domains.