2.A.37.2.7
Na⁺/H⁺ antiporter of 386 aas and 13 predicted TMSs, NapA. The 3-d structure is known (PDB# 4BWZ; 4BZ2; 4BZ3).  In the NapA structure, the core and dimerization domains are in different positions to those seen in the E. coli NhaA, and a negatively charged cavity is open to the outside. The extracellular cavity allows access to a strictly conserved aspartate residue thought to coordinate ion binding directly. To alternate access to this ion-binding site, however, requires a surprisingly large rotation of the core domain, some 20° against the dimerization interface (Lee et al. 2013). A  transmembrane lysine residue is essential for electrogenic transport in this and related Na+/H+ antiporters(Uzdavinys et al. 2017).