Structure and function of H(+)/K(+) pump mutants reveal Na(+)/K(+) pump mechanisms

Ion-transport mechanisms evolve by changing ion-selectivity, such as switching from Na(+) to H(+) selectivity in secondary-active transporters or P-type-ATPases. Here we study primary-active transport via P-type ATPases using functional and structural analyses to demonstrate that four simultaneous residue substitutions transform the non-gastric H(+)/K(+) pump, a strict H(+)-dependent electroneutral P-type ATPase, into a bona fide Na(+)-dependent electrogenic Na(+)/K(+) pump. Conversion of a H(+)-dependent primary-active transporter into a Na(+)-dependent one provides a prototype for similar studies of ion-transport proteins. Moreover, we solve the structures of the wild-type non-gastric H(+)/K(+) pump, a suitable drug target to treat cystic fibrosis, and of its Na(+)/K(+) pump-mimicking mutant in two major conformations, providing insight on how Na(+) binding drives a concerted mechanism leading to Na(+)/K(+) pump phosphorylation.