Computational study of the Na ⁺/H ⁺ antiporter from Vibrio parahaemolyticus

Sodium proton antiporters are ubiquitous membrane proteins that catalyze the exchange of Na ⁺ for protons throughout the biological world. The Escherichia coli NhaA is the archetypal Na ⁺/H ⁺ antiporter and is absolutely essential for survival in high salt concentrations under alkaline conditions. Its crystal structure, accompanied by extensive molecular dynamics simulations, have provided an atomically detailed model of its mechanism. In this study, we utilized a combination of computational methodologies in order to construct a structural model for the Na ⁺/H ⁺ antiporter from the gram-negative bacterium Vibrio parahaemolyticus. We explored its overall architecture by computational means and validated its stability and robustness. This protein belongs to a novel group of NhaA proteins that transports not only Na ⁺ and Li ⁺ as substrate ions, but K ⁺ as well, and was also found to miss a β-hairpin segment prevalent in other homologs of the Bacteria domain. We propose, for the first time, a structure of a prototype model of a β-hairpin-less NhaA that is selective to K ⁺. Better understanding of the Vibrio parahaemolyticus NhaA structure-function may assist in studies on ion transport, pH regulation and designing selective blockers.