A disulfide bridge mediated by cysteine 574 is formed in the dimer of the 70-kDa heat shock protein.

The 70-kDa heat shock protein (Hsp70) is predominantly present intracellularly as a monomer, but a small population is converted to dimers and oligomers under certain conditions. In the present study, we investigated the dimeric structure of human inducible Hsp70. As reported earlier, the C-terminal client-binding domain (amino acids 382-641) was required for the dimerization. A 40-amino acid deletion in the client-binding domain from either the N-terminus or C-terminus greatly enhanced the dimerization potential of Hsp70. Limited proteolysis indicated that the dimer formed through truncation from the C-terminus had a conformation similar to that of the non-truncated form. Truncation experiments demonstrated that the client-binding sub-domain (amino acids 382-520) with its adjacent region up to amino acid 541 was not sufficient for the dimerization but that the region up to amino acid 561 was sufficient. Interestingly, the dimer formed through truncation from the C-terminus acquired a homomeric disulfide bridge at Cys574.