How potassium affects the activity of the molecular chaperone Hsc70. II. Potassium binds specifically in the ATPase active site.
Crystallographic anomalous scattering from potassium at 1.7 A resolution reveals two monovalent ions that interact with MgADP and P(i) in the nucleotide binding cleft of wild-type recombinant bovine Hsc70 ATPase fragment. K+ at site 1 interacts with oxygens of the beta-phosphate of ADP, whereas K+ at site 2 interacts with an oxygen of P(i). Both K+ ions also interact with specific H2O molecules in the first hydration shell of the octahedrally coordinated Mg2+ ion and with specific protein ligands. In crystals that have Na+ present, K+ is replaced by a Na+ ion at site 1 and by a Na(+)-H2O pair at site 2. The K+ ions are positioned where they could stabilize binding of a beta,gamma-bidentate MgATP complex with Hsc70, as well as a transition state during ATP hydrolysis, suggesting that monovalent ions act as specific metal cofactors in the ATPase reaction of Hsc70.
Beckman Laboratories for Structural Biology, Stanford University School of Medicine, California 94305.
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Wilbanks
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McKay
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism*; D002414:Cations, Monovalent; D002417:Cattle; D002712:Chlorides / Q000378:metabolism; D018360:Crystallography, X-Ray; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D066298:In Vitro Techniques; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000378:metabolism*; D011188:Potassium / Q000502:physiology*; D011994:Recombinant Proteins
D002352:Carrier Proteins; D002414:Cations, Monovalent; D002712:Chlorides; D050883:HSC70 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D018832:Molecular Chaperones; D011994:Recombinant Proteins; D000251:Adenosine Triphosphatases; D011188:Potassium