The Putative Na<sup>+</sup>/H<sup>+</sup> Antiporter of <i>Vibrio cholerae</i>, Vc-NhaP2, Mediates the Specific K<sup>+</sup>/H<sup>+</sup> Exchange in Vivo
Bibliographic record
Abstract
The existence of bacterial K(+)/H(+) antiporters that prevent the overaccumulation of potassium in the cytoplasm was predicted by Peter Mitchell almost 50 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 a pH optimum of approximately 7.75 with an apparent K(m) 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 the structural determinants of the substrate specificity in alkali cation exchangers.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".