Interaction between the N-terminal and Middle Regions Is Essential for the in Vivo Function of HSP90 Molecular Chaperone

At the primary structure level, the 90-kDa heat shock protein (HSP90) is composed of three regions: the N-terminal (Met 1 –Arg 400 ), middle (Glu 401 –Lys 615 ), and C-terminal (Asp 621 –Asp 732 ) regions. In the present study, we investigated potential subregion structures of these three regions and their roles. Limited proteolysis revealed that the N-terminal region could be split into two fragments carrying residues Met 1 to Lys 281 (or Lys 283 ) and Glu 282 (or Tyr 284 ) to Arg 400 . The former is known to carry the ATP-binding domain. The fragments carrying the N-terminal two-thirds (Glu 401 –Lys 546 ) and C-terminal one-third of the middle region were sufficient for the interactions with the N- and C-terminal regions, respectively. Yeast HSC82 that carried point mutations in the middle region causing deficient binding to the N-terminal region could not support the growth of HSP82-depleted cells at an elevated temperature. Taken together, our data show that the N-terminal and middle regions of the HSP90 family protein are structurally divided into two respective subregions. Moreover, the interaction between the N-terminal and middle regions is essential for the in vivo function of HSP90 in yeast.