Structure of a Na+/H+ antiporter and insights into mechanism of action and regulation by pH

Carola Hunte (), Emanuela Screpanti, Miro Venturi, Abraham Rimon, Etana Padan () and Hartmut Michel ()
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Carola Hunte: Max Planck Institute of Biophysics
Emanuela Screpanti: Max Planck Institute of Biophysics
Miro Venturi: Max Planck Institute of Biophysics
Abraham Rimon: Hebrew University of Jerusalem
Etana Padan: Hebrew University of Jerusalem
Hartmut Michel: Max Planck Institute of Biophysics

Nature, 2005, vol. 435, issue 7046, 1197-1202

Abstract: Abstract The control by Na+/H+ antiporters of sodium/proton concentration and cell volume is crucial for the viability of all cells. Adaptation to high salinity and/or extreme pH in plants and bacteria or in human heart muscles requires the action of Na+/H+ antiporters. Their activity is tightly controlled by pH. Here we present the crystal structure of pH-downregulated NhaA, the main antiporter of Escherichia coli and many enterobacteria. A negatively charged ion funnel opens to the cytoplasm and ends in the middle of the membrane at the putative ion-binding site. There, a unique assembly of two pairs of short helices connected by crossed, extended chains creates a balanced electrostatic environment. We propose that the binding of charged substrates causes an electric imbalance, inducing movements, that permit a rapid alternating-access mechanism. This ion-exchange machinery is regulated by a conformational change elicited by a pH signal perceived at the entry to the cytoplasmic funnel.

Date: 2005
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DOI: 10.1038/nature03692

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