IDENTIFICATION AND STRUCTURAL CHARACTERIZATION OF THE ATP ADP-BINDINGSITE IN THE HSP90 MOLECULAR CHAPERONE/

Hsp90 molecular chaperones in eukaryotic cells play essential roles in the folding and activation of a range of client proteins involved in cell cycle regulation, steroid hormone responsiveness, and signal tran sduction. The biochemical mechanism of Hsp90 is poorly understood, and the involvement of ATP in particular is controversial. Crystal struct ures of complexes between the N-terminal domain of the yeast Hsp90 cha perone and ADP/ATP unambiguously identify a specific adenine nucleotid e binding site homologous to the ATP-binding site of DNA gyrase B. Thi s site is the same as that identified for the antitumor agent geldanam ycin, suggesting that geldanamycin acts by blocking the binding of nuc leotides to Hsp90 and not the binding of incompletely folded client po lypeptides as previously suggested. These results finally resolve the question of the direct involvement of ATP in Hsp90 function.