ATP-binding is stabilized by a stacking interaction within the binding site of Na+/K+ -ATPase

Site-directed mutagenesis was applied to modify phenylalanines (Phe(475)Trp, Phe(548)Tyr, and both) to generate mutants on the basis of molecular modeling of the ATP-binding domain of Na(+)/K(+)-ATPase, in order to characterize the forces that stabilize ATP in its binding pocket. Each of the mutants was examined by Raman difference spectroscopy, i.e., as a difference between the spectrum of the domain with and without bound ATP. It was shown that Phe(475) plays a key role in stabilizing ATP-binding by a stacking interaction. Phe(548) co-stabilizes ATP on the opposite site of the binding pocket and its type of interaction with ATP-binding differs from that of Phe(475).