NhaA family
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| Na+/H+ antiporter 1 | |||||||||||
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| Identifiers | |||||||||||
| Symbol | Na_H_antiport_1 | ||||||||||
| Pfam | PF06965 | ||||||||||
| InterPro | IPR004670 | ||||||||||
| TCDB | 2.A.36 | ||||||||||
| OPM superfamily | 106 | ||||||||||
| OPM protein | 1zcd | ||||||||||
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Na+/H+ antiporter A (NhaA) family (TC# 2.A.33) contains a number of bacterial sodium-proton antiporter (SPAP) proteins. These are integral membrane proteins that catalyse the exchange of H+ for Na+ in a manner that is highly pH dependent. Homologues have been sequenced from a number of bacteria and archaea. Prokaryotes possess multiple paralogues. A representative list of the proteins that belong to the NhaA family can be found in the Transporter Classification Database.
Proteins of the NhaA family are of 300-700 amino acyl residues in length. NhaA of E. coli is a homeodimer, each subunit consisting of a bundle of 12 tilted transmembrane α-helices (TMSs).[1][2][3][4][5]
Molecular dynamics simulations of NhaA enabled proposal of an atomically detailed model of antiporter function.[6] Three conserved aspartate residues are key to this 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.[6][7][8]
Function
Na+-H+ antiporters are integral membrane proteins that exchange Na+ for H+ across the cytoplasmic membrane and many intracellular membranes. They are essential for Na+, pH, and volume homeostasis, which are processes crucial for cell viability.[8][9] The E. coli protein probably functions in the regulation of the internal pH when the external pH is alkaline, and the protein effectively functions as a pH sensor.[7] It also uses the H+ gradient to expel Na+ from the cell. Its activity is highly pH dependent.[3][10]
The generalized transport reaction catalyzed by NhaA is:[6][11]
Na+ (in) + 2H+ (out) ⇌ Na+ (out) + 2H+ (in).
