Protein Folding Activity of Hsp70 Is Modified Differentially by the Hsp40 Co-chaperones Sis1 and Ydj1

Abstract

Specification of Hsp70 action in cellular protein metabolism may occur through the formation of specialized Hsp70:Hsp40 pairs. To test this model, we compared the ability of purified Sis1 and Ydj1 to regulate the ATPase and protein-folding activity of Hsp70 Ssa1 and Ssb1/2 proteins. Ydj1 and Sis1 could both functionally interact with Ssa1, but not the Ssb1/2 proteins, to refold luciferase. Interestingly, Ydj1:Ssa1 could promote up to four times more luciferase folding than Sis1:Ssa1. This functional difference was explored and could not be accounted for by differences in the ability of Sis1 and Ydj1 to regulate Ssa1 ATPase activity. Instead, differences in the chaperone function of Ydj1 and Sis1 were observed. Ydj1 was dramatically more effective than Sis1 at suppressing the thermally induced aggregation of luciferase. Paradoxically, Sis1 and Ydj1 could bind similar quantities of chemically denatured luciferase. The polypeptide binding domain of Sis1 was found to lie between residues 171-352 and correspond to its conserved carboxyl terminus. The conserved carboxyl terminus of Ydj1 is also known to participate in the binding of nonnative polypeptides. Thus, Ydj1 appears more efficient at assisting Ssa1 in folding luciferase because its contains a zinc finger-like region that is absent from Sis1. Ydj1 and Sis1 are structurally and functionally distinct Hsp40 proteins that can specify Ssa1 action by generating Hsp70:Hsp40 pairs that exhibit different chaperone activities.

ERdj4 and ERdj5 Are Required for Endoplasmic Reticulum-associated Protein Degradation of Misfolded Surfactant Protein C

“…This finding is similar to that reported for interaction of ERdj3 with unfolded substrates (Shen and Hendershot, 2005) and suggests that the C-terminal domain containing the Gly/Phe-rich region may bind unfolded/misfolded substrate directly. This hypothesis is also supported by the observation that yeast Sis1p directly binds substrate through its C-terminal domain and suggests that type II DnaJ proteins may have chaperone activity independently of BiP (Lu and Cyr, 1998). Although ERdj3 was also increased in cells expressing mutant SP-C, knockdown of ERdj4 resulted in accumulation of misfolded protein, indicating that endogenous ERdj3 could not compensate for loss of ERdj4.…”

The yeast Hsp110, Sse1p, exhibits high‐affinity peptide binding

“…As shown in Fig. 1, we found that the activity of the Ssa1p but not Sse1p was significantly enhanced by two cytosolic yeast Hsp40s, Hlj1p and Sis1p, which are, respectively, ER-and ribosome-associated Hsp70 co-chaperones that are known to interact with Ssa1p [19,23]. A mammalian Hsp40, Csp, which activates ATP hydrolysis by mammalian Hsc70 [24] also selectively stimulated ATP hydrolysis by Ssa1p.…”

Differential expression of three Paralichthys olivaceus Hsp40 genes in responses to virus infection and heat shock☆

“…3), indicating different roles in unstressed and stressed cells. Indeed, accumulating studies showed that Type I Hsp40s and Type II Hsp40s are not functionally equivalent [45,46], although they all regulate the Hsp70 ATP hydrolytic cycle [14,15] and direct non-native proteins to the peptide-binding site of Hsp70 [47]. For example, Type I Hsp40 Fig.…”

“…1, liver; 2, spleen; 3, head kidney; 4, posterior kidney; 5, skin; 6, heart; 7, muscle; 8, brain; 9, intestine; 10, ovary; 11, gill. proteins can function as co-chaperones independent of Hsp70 to suppress protein aggregation [48]. On the other hand, Type II Hsp40s appear to be less efficient as chaperones and need to interact with Hsp70 to suppress aggregation of model protein [46]. In yeast, Ydj1 (Type I Hsp40 homologue) is dramatically more effective than Sis1 (Type II Hsp40 homologue) in suppressing the thermally induced aggregation of luciferase and appears more efficient in assisting Ssa1 to fold luciferase [48].…”