DIFFERENTIAL INTERACTIONS OF P23 AND THE TPR-CONTAINING PROTEINS HOP,CYP40, FKBP52 AND FKBP51 WITH HSP90 MUTANTS

Hsp90 is required for the normal function of steroid receptors, but it s binding to steroid receptors is mediated by Hsc70 and several hsp-as sociated accessory proteins. An assortment of Hsp90 mutants were teste d for their abilities to interact with each of the following accessori es: Hop, Cyp40, FKBP52, FKBP51, and p23. Of the II Hsp90 mutants teste d, all were defective to some extent in associating with progestin (PR ) complexes. In every case, however, reduced PR binding correlated wit h a defect in binding of one or more accessories. Go-precipitation of mutant Hsp90 forms with individual accessories was used to map Hsp90 s equences required for accessory protein interactions. Mutation of Hsp9 0's highly conserved C-terminal EEVD to AAVD resulted in diminished in teractions with several accessory proteins, most particularly with Hop . Deletion of amino acids 661-677 resulted in loss of Hsp90 dimerizati on and also caused diminished interactions with all accessory proteins . Binding of p23 mapped most strongly to the N-terminal ATP-binding do main of Hsp90 while binding of TPR proteins mapped to the C-terminal h alf of Hsp90. These results and others further suggest that the N- and C-terminal regions of Hsp90 maintain important conformational links t hrough intramolecular interactions and/or intermolecular influences in homodimers.