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.
Wilbanks
S M
SM
Beckman Laboratories for Structural Biology, Stanford University School of Medicine, California 94305.
McKay
D B
DB
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