The NhaD family (TC# 2.A.62) belongs to the Ion Transporter (IT) Superfamily. A representative list of proteins belonging to the NhaD family can be found in the Transporter Classification Database.
The NhaD Na+/H+ antiporter has been characterized from two Vibrio species: V. parahaemolyticus and V. cholerae and in the haloalkaliphile, Alkalimonas amylolytica. These proteins and their homologues are 400-500 aas long and exhibit 10-13 TMSs. They catalyze Na+/H+ and Li+/H+ antiport. They exhibit activity at basic pH (8-10) with no activity at pH 7.5. The Amylolytica antiporter has low Na+ affinity and has optimal activity at 600 mM Na+. Homologues are found in proteobacteria of all groups, Flavobacteria and Chlamydia. Distant homologues of the IT superfamily are ubiquitous.
The generalized reaction catalyzed by NhaD is:
nH+ (in) + mNa+ (out) ⇌ nH+ (out) + mNa+ (in).