Sm. Wilbanks et Db. Mckay, HOW POTASSIUM AFFECTS THE ACTIVITY OF THE MOLECULAR CHAPERONE HSC70 .2. POTASSIUM BINDS SPECIFICALLY IN THE ATPASE ACTIVE-SITE, The Journal of biological chemistry, 270(5), 1995, pp. 2251-2257
Crystallographic anomalous scattering from potassium at 1.7 Angstrom r
esolution 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-phos
phate of ADP, whereas K+ at site 2 interacts with an oxygen of P-i. Bo
th K+ ions also interact with specific H2O molecules in the first hydr
ation 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(+)similar to H2O pair at site 2. The
K+ ions are positioned where they could stabilize binding of a beta,ga
mma-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.