Oligomerization of the 17-kDa peptide-binding domain of the molecular chaperone HSC70

Crystallographic and biochemical studies have indicated that the peptide-bi nding site of the molecular chaperone HSC70 is located in a small subdomain comprising a beta-sheet motif followed by a helical region, and there is s ome evidence of the involvement of this site in oligomerization of the prot ein. To determine the structure of this subdomain in solution and examine its in volvement in oligomerization of HSC70, a 17-kDa protein (residues 385-540 o f HSC70) consisting mainly of the peptide-binding site was constructed and analyzed for oligomerization properties. This small domain was found to bin d peptides and to form oligomers in solution, probably tetramers, which dis sociated into monomers on peptide binding in a manner comparable with that observed for the whole protein. Furthermore, in the 60-kDa fragment of HSC7 0, which is composed of the 17-kDa domain and the 44-kDa ATPase domain, not only were the oligomerization properties conserved, but dissociation of mu ltimeric species into monomers on ATP binding also occurred and peptide sti mulation of ATPase activity was restored. These results indicate that the i solated 17-kDa peptide-binding domain is necessary and sufficient for oligo merization of the whole protein, suggesting that the peptide-binding site m ay be involved in the oligomerization process.