title: Substrate-bound outward-open state of the betaine transporter BetP provides insights into Na+ coupling.
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.
authors.affiliation: 1] Structural Biology Department, Max-Planck Institute of Biophysics, Frankfurt am Main 60438, Germany [2] [3].
authors.forename: Camilo
authors.initials: C
authors.lastname: Perez
authors.affiliation: 1] Structural Biology Department, Max-Planck Institute of Biophysics, Frankfurt am Main 60438, Germany [2] [3].
authors.forename: Belinda
authors.initials: B
authors.lastname: Faust
authors.affiliation: 1] Computational Structural Biology Group, Max-Planck Institute of Biophysics, Frankfurt am Main 60438, Germany [2].
authors.forename: Ahmad Reza
authors.initials: AR
authors.lastname: Mehdipour
authors.affiliation: Institute of Chemistry-Analytical Chemistry, University of Graz, Graz 8010, Austria.
authors.forename: Kevin A
authors.initials: KA
authors.lastname: Francesconi
authors.affiliation: 1] Computational Structural Biology Group, Max-Planck Institute of Biophysics, Frankfurt am Main 60438, Germany [2].
authors.forename: Lucy R
authors.initials: LR
authors.lastname: Forrest
authors.affiliation: 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.
authors.forename: Christine
authors.initials: C
authors.lastname: Ziegler
mesh_terms: D002352:Carrier Proteins / Q000378:metabolism*; D004594:Electrophysiology; D004926:Escherichia coli / Q000378:metabolism; D050485:GABA Plasma Membrane Transport Proteins; D056004:Molecular Dynamics Simulation; D016297:Mutagenesis, Site-Directed; D012964:Sodium / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D050485:GABA Plasma Membrane Transport Proteins; C072207:betaine plasma membrane transport proteins; D012964:Sodium