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Crystal structure of the Na+/H+ antiporter NhaACrystal structure of the Na+/H+ antiporter NhaA
Structural highlights
Function[NHAA_ECOLI] Na(+)/H(+) antiporter that extrudes sodium in exchange for external protons. Catalyzes the exchange of 2 H(+) per Na(+). Can mediate sodium uptake when a transmembrane pH gradient is applied. Active at alkaline pH. Activity is strongly down-regulated below pH 6.5.[1] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThe 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. Structure of a Na+/H+ antiporter and insights into mechanism of action and regulation by pH.,Hunte C, Screpanti E, Venturi M, Rimon A, Padan E, Michel H Nature. 2005 Jun 30;435(7046):1197-202. PMID:15988517[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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