Interaction of HSP70 with J-domain co-chaperones

The Hsp70 chaperone system plays a part in many cellular functions, including protein folding, refolding of misfolded proteins, and solubilizing protein aggregates. These chaperones, however, require tight regulation of their activity and precise selection of substrates in order to perform their diverse protein functions.

This regulation is achieved by transition of the Hsp70 from the low-substrate-affinity ATP state to the high-affinity ADP state, which is, in turn, modulated by the conserved family of J-domain proteins (JDPs). JDP co-chaperones, through a direct interaction, dramatically increase Hsp70 ATP hydrolysis rates and consequently Hsp70 substrate affinity. Structurally, JDPs are composed of an N-terminal J-domain, G/F-rich disordered linker, two putative substrate binding domains (CTDI, CTDII), and a dimerization domain. Biochemical data have suggested that it is the J-domain that is necessary for functional interaction with the Hsp70s, yet the J-domain alone is not sufficient for Hsp70 activation.

Here we have used NMR to determine the roles of the JDP domains in interaction with Hsp70. While our data shows that the J-domain indeed has an essential role in Hsp70 interaction, we also, surprisingly, found that the presence of G/F rich linker completely abolished the interaction of JPD with Hsp70. Our preliminary results further indicate that the linker may have a regulatory role, preventing Hsp70 from binding by generating a conserved salt bridge with the J-domain, and mutations disrupting this salt bridge indeed returned the ability of the JDPs to bind to Hsp70.