Stimulation of the Weak ATPase Activity of Human Hsp90 by a Client Protein

immunophilin; nuclear receptor*Corresponding author Abbreviations used: Hsp, heat shock protein; Hip, Hsp-interacting protein; Hop, Hsp70-organising protein; PPAR,E-mail address of the correspond peroxisome proliferator-activated re binding protein; hGR, human gluco carboxymethylated a-lactalbumin; G 0022-2836/02/040787–12 $35.00/0in, Harvey W. Smith and Sophie E. Jackson* Heat shock protein 90 (Hsp90) is a molecular chaperone involved in the folding and assembly of a limited set of ‘‘client’ ’ proteins, many of which are involved in signal transduction pathways. In vivo, it is found in com-plex with additional proteins, including the chaperones Hsp70, Hsp40, Hip and Hop (Hsp-interacting and Hsp-organising proteins, respectively), as well as high molecular mass immunophilins, such as FKBP59, and the small acidic protein p23. The role of these proteins in Hsp90-mediated assembly processes is poorly understood. It is known that ATP binding and hydrolysis are essential for Hsp90 function in vivo and in vitro