MD simulation of the NhaA dimer in a model membrane bilayer. (A) The NhaA dimer is stable in a POPC membrane. Snapshots show the structure after an ∼1-µs MD (simulation S2/1). The periplasmic space is at the top. Protomers are colored wheat and green, and POPC lipids are white. A bound sodium ion is shown as a cyan sphere. Residues Asp163, Asp164, and Lys300 are partially visible in a stick representation. (B) View from the periplasm.