The enlightening encounter between structure and function in the NhaA Na+-H+ antiporter |
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Authors: | Padan Etana |
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Institution: | Department of Biological Chemistry, Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel. |
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Abstract: | Na(+)-H(+) antiporters are integral membrane proteins that exchange Na(+) for H(+) across the cytoplasmic membrane and many intracellular membranes. They are essential for Na(+), pH, and volume homeostasis, which are processes crucial for cell viability. Accordingly, antiporters are important drug targets in humans and underlie salt resistance in plants. Many Na(+)-H(+) antiporters are tightly regulated by pH. Escherichia coli NhaA, a prototype pH-regulated antiporter, exchanges 2H(+) for 1Na(+) (or Li(+)). The NhaA crystal structure has provided insight into the pH-regulated mechanism of antiporter action and revealed transmembrane segments, which are interrupted by extended mid-membrane chains that have since been found with variations in other ion-transport proteins. This novel structural fold creates a delicately balanced electrostatic environment in the middle of the membrane, which might be essential for ion binding and translocation. |
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