Crystal structure of the C-terminal 10-kDa subdomain of Hsc70.

The 70-kDa heat shock proteins (Hsp70), including the cognates (Hsc70), are molecular chaperones that prevent misfolding and aggregation of polypeptides in cells under both normal and stressed conditions. They are composed of two major structural domains: an N-terminal 44-kDa ATPase domain and a C-terminal 30-kDa substrate binding domain. The 30-kDa domain can be divided into an 18-kDa subdomain and a 10-kDa subdomain. Here we report the crystal structure of the 10-kDa subdomain of rat Hsc70 at 3.45 A. Its helical region adopted a helix-loop-helix fold. This conformation is different from the equivalent subdomain of DnaK, the bacterial homologue of Hsc70. Moreover, in the crystalline state, the 10-kDa subdomain formed dimers. The results of gel filtration chromatography further supported the view that this subdomain was self-associated. Upon gel filtration, Hsc70 was found to exist as a mixture of monomers, dimers, and oligomers, but the 60-kDa fragment was predominantly found to exist as monomers. These findings suggest that the alpha-helical region of the 10-kDa subdomain dictates the chaperone self-association.