ATP BINDING AND HYDROLYSIS ARE ESSENTIAL TO THE FUNCTION OF THE HSP90MOLECULAR CHAPERONE IN-VIVO

Hsp90 is an abundant molecular chaperone essential to the establishmen t of many cellular regulation and signal transduction systems, but rem ains one of the least well described chaperones. The biochemical mecha nism of protein folding by Hsp90 is poorly understood, and the direct involvement of ATP has been particularly contentious. Here we demonstr ate in vitro an inherent ATPase activity in both yeast Hsp90 and the E scherichia coil homologue HtpG, which is sensitive to inhibition by th e Hsp90-specific antibiotic geldanamycin. Mutations of residues implic ated in ATP binding and hydrolysis by structural studies abolish this ATPase activity in vitro and disrupt Hsp90 function in vivo. These res ults show that Hsp90 is directly ATP dependent in vivo, and suggest an ATP-coupled chaperone cycle for Hsp90-mediated protein folding.