Mechanism of Na+/H+ antiporting.
Na+/H+ antiporters are central to cellular salt and pH homeostasis. The structure of Escherichia coli NhaA was recently determined, but its mechanisms of transport and pH regulation remain elusive. We performed molecular dynamics simulations of NhaA that, with existing experimental data, enabled us to propose an atomically detailed model of antiporter function. Three conserved aspartates are key to our proposed mechanism: Asp164 (D164) is the Na+-binding site, D163 controls the alternating accessibility of this binding site to the cytoplasm or periplasm, and D133 is crucial for pH regulation. Consistent with experimental stoichiometry, two protons are required to transport a single Na+ ion: D163 protonates to reveal the Na+-binding site to the periplasm, and subsequent protonation of D164 releases Na+. Additional mutagenesis experiments further validated the model.
Arkin
Isaiah T
IT
D. E. Shaw Research, New York, NY 10036, USA.
Xu
Huafeng
H
Jensen
Morten Ø
MØ
Arbely
Eyal
E
Bennett
Estelle R
ER
Bowers
Kevin J
KJ
Chow
Edmond
E
Dror
Ron O
RO
Eastwood
Michael P
MP
Flitman-Tene
Ravenna
R
Gregersen
Brent A
BA
Klepeis
John L
JL
Kolossváry
István
I
Shan
Yibing
Y
Shaw
David E
DE
D001224:Aspartic Acid / Q000378:metabolism; D001665:Binding Sites; D003198:Computer Simulation; D003460:Crystallization; D003593:Cytoplasm / Q000378:metabolism; D004926:Escherichia coli / Q000254:growth & development / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport; D008954:Models, Biological; D008958:Models, Molecular; D016296:Mutagenesis; D019897:Periplasm / Q000378:metabolism; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011522:Protons; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000737:chemistry* / Q000378:metabolism*
D029968:Escherichia coli Proteins; C102839:NhaA protein, E coli; D011522:Protons; D017923:Sodium-Hydrogen Exchangers; D001224:Aspartic Acid; D012964:Sodium