Structure and transport mechanism of the sodium/protonantiporter MjNhaP1
- Max Planck Institute of Biophysics, Germany
Abstract
Sodium/proton antiporters are essential for sodium and pH homeostasis and play a major role in human health and disease. We determined the structures of the archaeal sodium/proton antiporter MjNhaP1 in two complementary states. The inward-open state was obtained by x-ray crystallography in the presence of sodium at pH8, where the transporter is highly active. The outward-open state was obtained by electron crystallography without sodium at pH4, where MjNhaP1 is inactive. Comparison of both structures reveals a 7{degree sign} tilt of the 6 helix bundle. 22Na+ uptake measurements indicate non-cooperative transport with an activity maximum at pH7.5. We conclude that binding of a Na+ ion from the outside induces helix movements that close the extracellular cavity, open the cytoplasmic funnel, and result in a ~5 Å vertical relocation of the ion binding site to release the substrate ion into the cytoplasm.
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© 2014, Paulino et al.
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Structure and transport mechanism of the sodium/protonantiporter MjNhaP1
eLife 3:e03583.
https://doi.org/10.7554/eLife.03583
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