pH- and sodium-induced changes in a sodium/proton antiporter

Cristina Batista Paulino, Werner Kuehlbrandt

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We examined substrate-induced conformational changes in MjNhaP1, an archaeal electroneutral Na+/H+-antiporter resembling the human antiporter NHE1, by electron crystallography of 2D crystals in a range of physiological pH and Na+ conditions. In the absence of sodium, changes in pH had no major effect. By contrast, changes in Na+ concentration caused a marked conformational change that was largely pH-independent. Crystallographically determined, apparent dissociation constants indicated similar to 10-fold stronger Na+ binding at pH 8 than at pH 4, consistent with substrate competition for a common ion-binding site. Projection difference maps indicated helix movements by about 2 angstrom in the 6-helix bundle region of MjNhaP1 that is thought to contain the ion translocation site. We propose that these movements convert the antiporter from the proton-bound, outward-open state to the Na+-bound, inward-open state. Oscillation between the two states would result in rapid Na+/H+ antiport.
Original languageEnglish
Article numbere01412
Pages (from-to)1-13
Number of pages13
Publication statusPublished - 28-Jan-2014
Externally publishedYes


  • sodium/proton antiporter
  • pH
  • sodium
  • cryo-EM

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