The Putative Na⁺/H⁺ Antiporter of Vibrio cholerae, Vc-NhaP2, Mediates the Specific K⁺/H⁺ Exchange in Vivo

Abstract

The existence of bacterial K+/H+ antiporters preventing the over-accumulation of potassium in the cytoplasm was predicted by Peter Mitchell almost fifty years ago. The importance of K+/H+ antiport for bacterial physiology is widely recognized but its molecular mechanisms remain underinvestigated. Here, we demonstrate that a putative Na+/H+ antiporter, Vc-NhaP2, protects cells of Vibrio cholerae growing at pH 6.0 from high concentrations of external K+. Resistance of V. cholerae to Na+ was found to be independent of Vc-NhaP2. When assayed in inside-out membrane vesicles derived from antiporter-deficient Escherichia coli, Vc-NhaP2 catalyzed the electroneutral K+(Rb+)/H+ exchange with pH optimum at ~7.75 with an apparent Km for K+ of 1.62 mM. In the absence of K+ it exhibited Na+/H+ antiport, albeit rather weakly. Interestingly, while Vc-NhaP2 cannot exchange Li+ for protons, elimination of functional Vc-NhaP2 resulted in a significantly higher Li+ resistance of V. cholerae cells growing at pH 6.0, suggesting the possibility of Vc-NhaP2-mediated Li+/K+ antiport. The peculiar cation specificity of Vc-NhaP2 and the presence of its two additional paralogues in the same genome make this transporter an attractive model for detailed analysis of structural determinants of the substrate specificity in alkali cation exchangers.

Na + /H + Antiport Is Essential for Yersinia pestis Virulence

“…1) (4). However, recent detailed biochemical characterization of NhaP-type antiporters NhaP-1 and NhaP-2 from Vibrio cholerae revealed that these antiporters mediate K ϩ /H ϩ exchange rather than Na ϩ /H ϩ exchange under physiological conditions (6,7). By analogy, we predict that the Y. pestis NhaP protein has a similar cation preference ( Fig.…”

Growth Inhibition by External Potassium of Escherichia coli Lacking PtsN (EIIA Ntr ) Is Caused by Potassium Limitation Mediated by YcgO

“…However, we did not observe any significant differences in the growth rates between MC4100 and its ⌬ycgO derivative in the low-osmolarity media employed in the aforementioned study (data not shown). YcgO belongs to the CPA1 family of proteins that mediate monovalent cation/proton antiport (55), and its orthologs in Vibrio parahaemolyticus (56) and Vibrio cholerae (57) have been reported to mediate K ϩ efflux by functioning as K ϩ /H ϩ antiporters. It is thus plausible that YcgO-mediated K ϩ efflux may occur via K ϩ /H ϩ antiport.…”

A novel Na+(K+)/H+ antiporter plays an important role in the growth of Acetobacter tropicalis SKU1100 at high temperatures via regulation of cation and pH homeostasis

“…These characteristics are different from those of EcNhaA (Padan et al, 2004) or PaNhaA (Utsugi et al, 1998) both in terms of substrate specificity and optimum pH, but similar to those of HpNhaA in terms of pH optimum (Inoue et al, 1999), and to those of BsNhaK (Fujisawa et al, 2005) in terms of substrate specificity. The activity of both VpNhaP2 (Radchenko et al, 2006) and VcNhaP2 (Resch et al, 2010) is similar to that of At-NhaK2 for K + at alkaline pH and Na + at relatively neutral pH (pH 7.75). Furthermore, yeast antiporters possess properties similar to those of At-NhaK2; the Nha1 antiporter of S. cerevisiae can efflux both Na + and K + at acidic pH, suggesting greater importance for K + tolerance (BaAueIos et al, 1998), and S. pombe Sod2 and Sod22 exhibit broad substrate specificity at acidic pH (Papouskova and Sychrova, 2007).…”

“…NhaP2 of Vibrio parahaemolyticus (VpNhaP2) was shown to be specifically involved in K + /H + exchange at alkaline pH, while NhaA and NhaB possess certain K + exchange activity in addition to Na + transport (Radchenko et al, 2006). Furthermore, NhaP2 of V. cholerae (VcNhaP2), which is able to catalyze electroneutral K + (Rb + )/H + exchange with a pH optimum of approximately 7.75, was shown to be essential for resistance to high external K + concentrations during growth at pH 6.0 (Resch et al, 2010). Similarly, B. subtilis NhaK (BsNhaK) has the ability to extrude several cations, including K + , Li + , Rb + , as well as Na + (Fujisawa et al, 2005).…”

“…A large number of adaptive strategies for pH homeostasis have been reported, including Na + /H + antiporters, secondary sodium pumps, which play a crucial role by controlling intracellular Na + and H + concentrations in a pH-dependent manner (Häse et al, 2001). Several families of bacterial Na + /H + antiporters have been reported and characterized in detail (Hunte et al, 2005;Karpel et al, 1991;Mesbah et al, 2009;Minato et al, 2013;Padan et al, 2004;Pinner et al, 1993a;Quinn et al, 2012;Radchenko et al, 2006;Resch et al, 2010). Characterization of these individual antiporters has provided insight into their physiological role and importance in certain growth environments.…”