Abstract
The 70-kDa heat shock protein (Hsp70), one of the major stress-inducible molecular chaperones, is localized not only in the cytosol, but also in extracellular milieu in mammals. Hsp70 interacts with various cell surface glycolipids including sulfatide (3'-sulfogalactosphingolipid). However, the molecular mechanism, as well as the biological relevance, underlying the glycolipid-Hsp70 interaction is unknown. Here we report that sulfatide promotes Hsp70 oligomerization through the N-terminal ATPase domain, which stabilizes the binding of Hsp70 to unfolded protein in vitro. We find that the Hsp70 oligomer has apparent molecular masses ranging from 440 kDa to greater than 669 kDa. The C-terminal peptide-binding domain is dispensable for the sulfatide-induced oligomer formation. The oligomer formation is impaired in the presence of ATP, while the Hsp70 oligomer, once formed, is unable to bind to ATP. These results suggest that sulfatide locks Hsp70 in a high-affinity state to unfolded proteins by clustering the peptide-binding domain and blocking the binding to ATP that induces the dissociation of Hsp70 from protein substrates.
Highlights
Molecular chaperones constitute the central core of a protein quality control system
We previously demonstrated that sulfatide induces the formation of the high molecular-weight (HMW) Hsp70 based on the results of native-polyacrylamide gel electrophoresis (PAGE) analysis on Hsp70-lipid interaction [24]
We found that the binding of sulfatide to Hsp70 induces the formation of HMW
Summary
Molecular chaperones constitute the central core of a protein quality control system. When unfolded proteins are generated, molecular chaperones bind to them, thereby preventing their non-functional, cytotoxic aggregate formation [1]. In the cytosol of mammalian cells, the stress-inducible 70-kDa heat shock protein (Hsp70) is one of the major molecular chaperones that are highly expressed under stress conditions [2,3]. Hsp has an intrinsic ATPase activity that regulates association and dissociation between Hsp and protein substrates [4,5,6,7,8,9]. In the ATP-bound state, Hsp shows low affinity for protein substrates. When Hsp hydrolyzes ATP to ADP, the protein substrates are tightly bound to Hsp
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