J Proteins Catalytically Activate Hsp70 Molecules to Trap a Wide Range of Peptide Sequences

Howard Hughes Medical Institute, Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Molecular Cell (Impact Factor: 14.02). 12/1998; 2(5):593-603. DOI: 10.1016/S1097-2765(00)80158-6
Source: PubMed


Proteins of the Hsp70 family of ATPases, such as BiP, function together with J proteins to bind polypeptides in numerous cellular processes. Using a solid phase binding assay, we demonstrate that a conserved segment of the J proteins, the J domain, catalytically activates BiP molecules to bind peptides in its immediate vicinity. The J domain interacts with the ATP form of BiP and stimulates hydrolysis resulting in the rapid trapping of peptides, which are then only slowly released upon nucleotide exchange. Activation by the J domain allows BiP to trap peptides or proteins that it would not bind on its own. These results explain why BiP and probably all other Hsp70s can interact with a wide range of substrates and suggest that the J partner primarily determines the substrate specificity of Hsp70s.

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    • "Other stabilizing mechanisms cannot be excluded. For instance, even molecular chaperones, including GroEL, hsp70, TF, calnexin, and calrecticulin, were reported to recognize their substrates mainly through the non-hydrophobic interactions, such as electrostatic interactions and glycan-binding [79–82]. "
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    • "Most strikingly, PD variants showed enhanced interaction with J-proteins, which are involved in the folding function (hTid-1S and hTid-1L) as well as import reaction (DnaJC19) as indicated by their ability to get the ATPase activity stimulated through J-domain. In general, J-class protein family members are known to interact transiently with the ATPase domain of Hsp70s in ATP-bound conformation via their conserved J-domain (51). In vivo, the folding cycle of Hsp70 is initiated in ATP-bound conformation (21). "
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    • "We have assumed that a single BiP is activated per Sec63 molecule located at the ER membrane. In vitro studies have indicated that the BiP-Sec63 interaction occurs transiently, and suggest that one Sec63 molecule could potentially activate at least ten BiP molecules [38]. On average, E. coli experiments have determined that incoming proteins present a new Hsp70 binding site every 25 to 35 amino acids [46] which is consistent with S. cerevisiae literature that estimates a minimum of six to seven molecules of BiP bound to the endogeneous protein, ppαF [47]. "
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