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TitleSpecific protonation of acidic residues confers K selectivity to the gastric proton pump.
Journal, issue, pagesJ Biol Chem, Vol. 300, Issue 1, Page 105542, Year 2024
Publish dateDec 10, 2023
AuthorsHridya Valia Madapally / Kazuhiro Abe / Vikas Dubey / Himanshu Khandelia /
PubMed AbstractThe 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 ...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-Å 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.
External linksJ Biol Chem / PubMed:38072058 / PubMed Central
MethodsEM (single particle)
Resolution2.51 Å
Structure data

37391

8wa5

EMDB-37391, PDB-8wa5:
Cryo-EM structure of the gastric proton pump Y799W/E936Q mutant in K+-occluded (K+)E2-AlF state
Method: EM (single particle) / Resolution: 2.51 Å

Chemicals

ChemComp-K:
Unknown entry

ChemComp-ALF:
TETRAFLUOROALUMINATE ION

ChemComp-MG:
Unknown entry

ChemComp-CLR:
CHOLESTEROL

ChemComp-PCW:
1,2-DIOLEOYL-SN-GLYCERO-3-PHOSPHOCHOLINE / DOPC, phospholipid*YM

ChemComp-NAG:
2-acetamido-2-deoxy-beta-D-glucopyranose

ChemComp-HOH:
WATER

Source
  • sus scrofa (pig)
KeywordsMEMBRANE PROTEIN / P-type ATPase / gastric proton pump / primary transporter / transporter

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