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

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Hunte,  Carola
Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Max Planck Society;

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Screpanti,  Emanuela
Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Max Planck Society;

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Venturi,  Miro
Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Max Planck Society;

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Michel,  Hartmut
Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Max Planck Society;

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Citation

Hunte, C., Screpanti, E., Venturi, M., Rimon, A., Padan, E., & Michel, H. (2005). Structure of a Na+/H+ antiporter and insights into mechanism of action and regulation by pH. Nature, 435(7046), 1197-1202. doi:10.1038/nature03692.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0024-DA46-D
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.