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Nat Commun. 2014 Jul 15;5:4231. doi: 10.1038/ncomms5231.

Substrate-bound outward-open state of the betaine transporter BetP provides insights into Na+ coupling.

Author information

1
1] Structural Biology Department, Max-Planck Institute of Biophysics, Frankfurt am Main 60438, Germany [2] [3].
2
1] Computational Structural Biology Group, Max-Planck Institute of Biophysics, Frankfurt am Main 60438, Germany [2].
3
Institute of Chemistry-Analytical Chemistry, University of Graz, Graz 8010, Austria.
4
1] Structural Biology Department, Max-Planck Institute of Biophysics, Frankfurt am Main 60438, Germany [2] Institute of Biophysics and Biophysical Chemistry, University of Regensburg, Regensburg 95053, Germany.

Abstract

The Na(+)-coupled betaine symporter BetP shares a highly conserved fold with other sequence unrelated secondary transporters, for example, with neurotransmitter symporters. Recently, we obtained atomic structures of BetP in distinct conformational states, which elucidated parts of its alternating-access mechanism. Here, we report a structure of BetP in a new outward-open state in complex with an anomalous scattering substrate, adding a fundamental piece to an unprecedented set of structural snapshots for a secondary transporter. In combination with molecular dynamics simulations these structural data highlight important features of the sequential formation of the substrate and sodium-binding sites, in which coordinating water molecules play a crucial role. We observe a strictly interdependent binding of betaine and sodium ions during the coupling process. All three sites undergo progressive reshaping and dehydration during the alternating-access cycle, with the most optimal coordination of all substrates found in the closed state.

PMID:
25023443
PMCID:
PMC4745115
DOI:
10.1038/ncomms5231
[Indexed for MEDLINE]
Free PMC Article
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