Physiology of the Vc-NhaP paralogous group of cation–proton antiporters in Vibrio cholerae
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The genome of Vibrio cholerae encodes three cation–proton antiporters of NhaP-type, Vc-NhaP1, 2, and 3. To examine physiological roles of Vc-NhaP antiporters, triple ΔnhaP1ΔnhaP2ΔnhaP3 and single ΔnhaP3 deletion mutants of V. cholerae were constructed and characterized. Vc-NhaP3 was, for the first time, cloned and biochemically characterized. Activity measurements on the inside-out membrane vesicle experimental model defined Vc-NhaP3 as a potassium-specific cation–proton antiporter. While elimination of functional Vc-NhaP3 resulted in only minor growth defect in potassium-rich medium at pH 6.0, the triple Vc-NhaP mutant demonstrated severe growth defects at both low and high [K+] at pH 6.0 and failed to grow at high [K+] in mildly alkaline (pH 8.0 and 8.5) media, as well. Expressed from a plasmid, neither of the Vc-NhaP paralogues was able to complement the severe potassium-sensitive phenotype of the triple deletion mutant completely. Vc-NhaP1 provided much better complementation at acidic pH compared to Vc-NhaP2, despite the fact that Vc-NhaP2 showed much higher antiport activity in sub-bacterial vesicles. In mildly alkaline pH only Vc-NhaP2 complemented the potassium-sensitive phenotype of the triple deletion mutant. Taken together, these data suggest that in vivo all three isoforms operate in concert, contributing to K+ resistance of V. cholerae. We suggest that the Vc-NhaP paralogue group might play a role in passing gastric acid barrier by ingested V. cholerae cells.
KeywordsPotassium resistance NhaP Cation–proton antiporters Vibrio cholerae
This research was supported by Grant # 227414-2012 from the Natural Sciences and Engineering Research Council of Canada (to CR, MM and PD) and by grant from the National Institutes of Health 1 R21 AI109435-01A1 (to CBS and CCH). We would like to thank Dr. T. Nakamura (Niigata University of Pharmacy and Applied Life Sciences, Niigata, Japan) who kindly provided us with TO114 strain of E. coli. Many thanks are also due to Dr. J. L. Winogrodzki for her help with the analysis of membrane topology of Vc-NhaP proteins and Drs. M. J. Quinn and E. J. Lind for the construction of some of the engineered strains used in this work.
MM, CBS and CTR performed most of the experiments, contributed to data organization and manuscript review; MM performed most of the growth experiments as well as all membrane isolation and antiport measurements in vesicles; CBS performed crucial part of the molecular cloning, as well as some growth experiments, and reviewed the manuscript; CTR designed some experiments, contributed to the activity measurements in vesicles and Western blot analysis; critically reviewed data, contributed to the writing of manuscript; CCH and PD designed all the experiments, critically reviewed and edited data, PD wrote and reviewed manuscript.
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