ATP-induced protein-Hsp70 complex dissociation requires K+ but not ATP hydrolysis.
The molecular chaperone proteins, particularly Hsp60 and Hsp70, have been implicated in essential cell functions under both normal and stress conditions (reviewed in refs 1-5). Members of the family of heat-shock proteins of M(r) 70K, Hsp70, bind to unfolded proteins and short peptides. Addition of Mg-ATP results in the dissociation of the substrate polypeptides from the chaperone, but as ATP-gamma S (an ATP analogue that is only slowly hydrolysable) cannot substitute for ATP in this reaction, it has been concluded that ATP hydrolysis is necessary to dissociate Hsp70-substrate protein complexes. By independently measuring the rates of ATP hydrolysis and substrate protein dissociation, we show here that Mg-ATP binding but not Mg-ATP hydrolysis is essential for substrate dissociation. We also show that there is an absolute requirement for K+ for the effect of Mg-ATP: only the combination of K+ and Mg-ATP will cause the conformational change in Hsp70 that is necessary for substrate dissociation. Moreover, in the absence of K+, Mg-ATP favours complex formation. We consider these results in terms of a G-protein-like model.
Palleros
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DR
Department of Chemistry and Biochemistry, University of California, Santa Cruz 95064.
Reid
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KL
Shi
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Welch
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WJ
Fink
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AL
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D004926:Escherichia coli; D019204:GTP-Binding Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D007768:Lactalbumin / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism; D008836:Micrococcal Nuclease / Q000378:metabolism; D009154:Mutation; D011188:Potassium / Q000378:metabolism*; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence
D006360:Heat-Shock Proteins; D000255:Adenosine Triphosphate; D007768:Lactalbumin; D008836:Micrococcal Nuclease; D000251:Adenosine Triphosphatases; D019204:GTP-Binding Proteins; D008274:Magnesium; D011188:Potassium