Role of the C-terminal cytoplasmic tail of the NhaP2 antiporter from Vibrio cholerae in transmembrane ion transport

Abstract

Although the importance of cation/proton antiporters in cellular physiology is well recognized and widely studied, many antiport systems remain underinvestigated. In this work, I report the phenotypic and biochemical effects of deletion of the cytoplasmic C-terminal tail of the NhaP2 antiporter from Vibrio cholerae (Vc-NhaP2). Namely, deletion of the C-terminal tail results in diminished K+/H+ and Na+/H+ antiport activity, as well as a 5-fold decrease in affinity for its major substrate, K+ (measured as the apparent Km at pH 7.5). Furthermore, reconstitution of antiport activity in the truncation mutant upon addition of exogenous C-terminal tail is demonstrated. Currently, the only known mechanism of antiport is for NhaA, which lacks a cytoplasmic tail. Therefore, these results suggest that NhaP2 may employ a novel mechanism of antiport in which the cytoplasmic tail is directly or indirectly involved.