8wa5

Publication Abstract from PubMed

The gastric proton pump (H(+),K(+)-ATPase) transports a proton into the stomach lumen for every K(+) ion exchanged in the opposite direction. In the lumen-facing state of the pump (E2), the pump selectively binds K(+) despite the presence of a 10-fold higher concentration of Na(+). The molecular basis for the ion selectivity of the pump is unknown. Using molecular dynamics simulations, free energy calculations, and Na(+) and K(+)-dependent ATPase activity assays, we demonstrate that the K(+) selectivity of the pump depends upon the simultaneous protonation of the acidic residues E343 and E795 in the ion-binding site. We also show that when E936 is protonated, the pump becomes Na(+) sensitive. The protonation-mimetic mutant E936Q exhibits weak Na(+)-activated ATPase activity. A 2.5-A resolution cryo-EM structure of the E936Q mutant in the K(+)-occluded E2-Pi form shows, however, no significant structural difference compared with wildtype except less-than-ideal coordination of K(+) in the mutant. The selectivity toward a specific ion correlates with a more rigid and less fluctuating ion-binding site. Despite being exposed to a pH of 1, the fundamental principle driving the K(+) ion selectivity of H(+),K(+)-ATPase is similar to that of Na(+),K(+)-ATPase: the ionization states of the acidic residues in the ion-binding sites determine ion selectivity. Unlike the Na(+),K(+)-ATPase, however, protonation of an ion-binding glutamate residue (E936) confers Na(+) sensitivity.

Specific protonation of acidic residues confers K(+) selectivity to the gastric proton pump.,Madapally HV, Abe K, Dubey V, Khandelia H J Biol Chem. 2024 Jan;300(1):105542. doi: 10.1016/j.jbc.2023.105542. Epub 2023 , Dec 10. PMID:38072058^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.