Heat-induced oligomerization of the molecular chaperone Hsp90 - Inhibitionby ATP and geldanamycin and activation by transition metal oxyanions

It has been previously reported that heat shock protein 90 (Hsp90) oligomer izes at high temperatures and displays concomitantly a novel chaperone acti vity (Yonehara, M., Minami, Y., Kawata, Y., Nagai, J., and Yahara, I. (1996 ) J. Biol. Chem., 271, 2641-2645). In order to better define these oligomer ization properties at high temperatures and to know whether they are influe nced by modulators of Hsp90 function, heat-induced oligomerization of highl y purified dimeric Hsp90 has been investigated over a wide range of tempera ture and protein concentrations by native polyacrylamide gel electrophoresi s and size exclusion chromatography. Whereas below 50 degrees C, the dimeri c form is maintained over a large range of concentrations, at the critical temperature of 50 degrees C, a sharp transition from dimeric to higher orde r oligomeric species takes place within minutes, in a highly ordered proces s, suggesting that a conformational change, leading to the appearance of a new oligomerization site, occurs in Hsp90 dimer. Moreover, at and above the critical temperature, the extent of oligomerization increases with Hsp90 c oncentration. Formation of high order oligomers at high temperatures is sensitive to modu lators of Hsp90 function. ATP and geldanamycin, both known to bind to the s ame pocket of Hsp90, are inhibitors of this process, whereas molybdate, van adate, and Nonidet P-40, which are thought to increase surface hydrophobici ty of the protein, are activators. Thus, oligomerization of Hsp90 at high t emperatures may be mediated through hydrophobic interactions that are hinde red by ligands and favored by transition metal oxyanions. The fact that the heat-induced oligomerization of Hsp90 is affected by spec ific ligands that modulate its properties also suggests that this process m ay be involved in cell protection during heat shock.