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

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Paulino,  Cristina
Department of Structural Biology, Max Planck Institute of Biophysics, Max Planck Society;

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Kühlbrandt,  Werner       
Department of Structural Biology, Max Planck Institute of Biophysics, Max Planck Society;

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Citation

Paulino, C., & Kühlbrandt, W. (2014). pH- and sodium-induced changes in a sodium/proton antiporter. eLife, 3: e01412. doi:10.7554/eLife.01412.


Cite as: https://hdl.handle.net/11858/00-001M-0000-0024-D464-0
Abstract
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 Nav concentration caused a marked conformational change that was largely pH-independent. Crystallographically determined, apparent dissociation constants indicated ∼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 Å 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