Cloning, expression, purification and preliminary X-­ray crystallographic studies of yeast Hsp40 Sis1 complexed with Hsp70 Ssa1 C-terminal lid domain

Heat-shock protein 70 (Hsp70) plays essential roles in a number of cellular processes such as protein folding, assembly and translocation. Heat-shock protein 40 (Hsp40) transiently interacts with Hsp70 and facilitates Hsp70 functions in these processes within cells. Hsp40 recognizes and binds non-native polypeptide and delivers it to Hsp70. Hsp40 can then stimulate the ATPase activity of Hsp70 to refold the polypeptide. To investigate the molecular mechanism by which Hsp40 interacts with Hsp70 to transport the non-native polypeptide, Saccharomyces cerevisiae Hsp40 Sis1 C-terminal peptide-binding fragment complexed with Hsp70 Ssa1 C-terminal lid domain has been produced and crystallized. The complex crystals diffract to 3.3 Å and belong to the space group P4₁2₁2 or P4₃2₁2, with unit-cell parameters a = 112.17, c = 171.31 Å. Structure determination by the MAD method is under way.