2.A.62 The NhaD Na⁺:H⁺ Antiporter (NhaD) Family The NhaD Na⁺/H⁺ antiporter has been characterized from two Vibrio species: V. parahaemolyticus and V. cholerae (Nozaki et al., 1998; Ostroumov et al., 2002) and in the haloalkaliphile, Alkalimonas amylolytica (Liu et al., 2005). 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 NhaD family is a constituent of the IT superfamily (Prakash et al., 2003). The generalized reaction catalyzed by NhaD is: nH⁺ (in) + mNa⁺ (out) ⇌ nH⁺ (out) + mNa⁺ (in). (n and m are unknown, but are probably 1 or 2)
This family belongs to the IT Superfamily.
References:
Barrero-Gil, J., A. Rodríguez-Navarro, and B. Benito. (2007). Cloning of the PpNHAD1 transporter of Physcomitrella patens, a chloroplast transporter highly conserved in photosynthetic eukaryotic organisms. J Exp Bot 58: 2839-2849.
Cui, Y., B. Cheng, Y. Meng, C. Li, H. Yin, P. Xu, and C. Yang. (2016). Expression and functional analysis of two NhaD type antiporters from the halotolerant and alkaliphilic Halomonas sp. Y2. Extremophiles 20: 631-639.
Kurz, M., A.N. Brünig, and E.A. Galinski. (2006). NhaD type sodium/proton-antiporter of Halomonas elongata: a salt stress response mechanism in marine habitats? Saline Systems 2: 10.
Liu, J., Y. Xue, Q. Wang, Y. Wei, T.H. Swartz, D.B. Hicks, M. Ito, Y. Ma, and T.A. Krulwich. (2005). The activity profile of the NhaD-type Na⁺(Li⁺)/H⁺ antiporter from the Soda Lake haloalkaliphile Alkalimonas amylolytica is adaptive for the extreme environment. J. Bacteriol. 187: 7589-7595.
Melo, A.M., N.A. Felix, J.N. Carita, L.M. Saraiva, and M. Teixeira. (2006). The Na⁺/H⁺ antiporter of the thermohalophilic bacterium Rhodothermus marinus. Biochem. Biophys. Res. Commun. 348: 1011-1017.
Nozaki, K., T. Kuroda, T. Mizushima, and T. Tsuchiya. (1998). A new Na⁺/H⁺ antiporter, NhaD, of Vibrio parahaemolyticus. Biochim. Biophys. Acta 1369: 213-220.
Ostroumov, E., J. Dzioba, P. Loewen, and P. Dibrov. (2002). Asp³⁴⁴ and Thr³⁴⁵ are critical for cation exchange mediated by NhaD, Na⁺/H⁺ antiporter of Vibrio cholerae. Biochim. Biophys. Acta 1564: 99-106.
Prakash, S., G. Cooper, S. Singhi, and M.H. Saier, Jr. (2003). The ion transporter superfamily. Biochim. Biophys. Acta 1618: 79-92.
Zhong, N.Q., L.B. Han, X.M. Wu, L.L. Wang, F. Wang, Y.H. Ma, and G.X. Xia. (2012). Ectopic expression of a bacterium NhaD-type Na⁺/H⁺ antiporter leads to increased tolerance to combined salt/alkali stresses. J Integr Plant Biol 54: 412-421.
Examples:
TC#	Name	Organismal Type	Example
2.A.62.1.1	NhaD Na⁺/H⁺ antiporter	Bacteria	NhaD of Vibrio parahaemolyticus

2.A.62.1.2	NhaD Na⁺(Li⁺)/H⁺ antiporter (Liu et al., 2005). AaNhaD is from the soda lake alkaliphile, Alkalimonas amylolytica, is crucial for the bacterium's resistance to salt/alkali stresses (Zhong et al. 2012).	Proteobacteria	*NhaD of Alkalimonas amylolytica* (AAX63482)**

2.A.62.1.3	*Chloroplast Na⁺/H⁺ antiporter of 582 aas, NhaD (Barrero-Gil et al.* 2007). Mediates ionic homeostasis in chloroplasts from red algae to flowering plants ((Barrero-Gil et al. 2007).**	Plants	*NhaD of Physcomitrella patens* (Moss)**

2.A.62.1.4	*Na⁺/H⁺ antiporter, NhaD of 495 aas; involved in the response to salt stress and adaptation to a marine environment (Kurz et al.* 2006).**	Proteobacteria	NhaD of the halophilic eubacterium, Halomonas elongata

2.A.62.1.5	Sodium/proton antiporter, NhaD1, of 488 aas and 14 TMSs. Two NhaD homologues that catalyze Na⁺/H⁺ antiport were identified from this halotolerant and alkaliphilic strain isolated from sodium enriched black liquor. They exhibit 72% identity and have similar binding affinities for Na⁺ and Li⁺, while having different pH profiles. Ha-NhaD1 was active at pH 6.0 and most active at pH 8.0-8.5, whereas Ha-NhaD2 lacked activity at pH 6.0 but exhibited maximal activity at pH 9.5 or higher. Residues involved in transport were identified (Cui et al. 2016).		*NhaD1 of Halomonas* sp. Y2**

2.A.62.1.6	Na⁺ or Li⁺/H⁺ antiporter, NhaD, of 477 aas and 14 TMSs. It extrudes Na⁺ or Li⁺ in exchange for H⁺ (Dzioba et al. 2002). Residues important for function have been identified (Ostroumov et al. 2002; Habibian et al. 2005).		NhaD of Vibrio cholerae

2.A.62.1.7	NhaD homologue of 400 aas and 11 TMSs		NhaD of Hyphomicrobium zavarzinii