Molecular mechanisms of gating in the calcium-activated chloride channel bestrophin
Bestrophin (BEST1-4) ligand-gated chloride (Cl-) channels are activated by calcium (Ca2+). Mutation of BEST1 causes retinal disease. Partly because bestrophin channels have no sequence or structural similarity to other ion channels, the molecular mechanisms underlying gating are unknown. Here, we present a series of cryo-electron microscopy structures of chicken BEST1, determined at 3.1 Å resolution or better, that represent the channel's principal gating states. Unlike other channels, opening of the pore is due to the repositioning of tethered pore-lining helices within a surrounding protein shell that dramatically widens a neck of the pore through a concertina of amino acid rearrangements. The neck serves as both the activation and the inactivation gate. Ca2+ binding instigates opening of the neck through allosteric means whereas inactivation peptide binding induces closing. An aperture within the otherwise wide pore controls anion permeability. The studies define a new molecular paradigm for gating among ligand-gated ion channels.
Atomic coordinates and cryo-EM density maps of have been deposited with the PDB and Electron Microscopy Data Bank with the accession numbers: 6N23 (BEST1405, inactivated; EMD-9321), 6N24 (BEST1345 W287F mutant, Ca2+-free; EMD-9322), 6N25 (BEST1345 W287F mutant, Ca2+-bound; EMD-9323), 6N26 ( BEST1345 Ca2+-free closed state; EMD-9324), 6N27 (BEST1345 Ca2+-bound closed state; EMD-9325), and 6N28 ( BEST1345 Ca2+-bound open state; EMD-9326).
BEST1 in a calcium-bound inactivated stateProtein Databank, 6N23.
BEST1 open state W287F mutant, calcium-freeProtein Databank, 6N24.
BEST1 open state W287F mutant, calcium-boundProtein Databank, 6N25.
BEST1 calcium-free closed state (deactivated)Protein Databank, 6N26.
BEST1 calcium-bound closed stateProtein Databank, 6N27.
BEST1 calcium-bound open stateProtein Databank, 6N28.
BEST1 in a calcium-bound inactivated stateElectron Microscopy Data Bank, EMD-9321.
BEST1 open state W287F mutant, calcium-freeElectron Microscopy Data Bank, EMD-9322.
BEST1 open state W287F mutant, calcium-boundElectron Microscopy Data Bank, EMD-9323.
BEST1 calcium-free closed state (deactivated)Electron Microscopy Data Bank, EMD-9324.
BEST1 calcium-bound closed stateElectron Microscopy Data Bank, EMD-9325.
BEST1 calcium-bound open stateElectron Microscopy Data Bank, EMD-9326.
Article and author information
National Institutes of Health (R01-GM110396)
- Stephen Barstow Long
National Cancer Institute (P30 CA008748)
- Stephen Barstow Long
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
- Kenton Jon Swartz, National Institute of Neurological Disorders and Stroke, National Institutes of Health, United States
- Received: October 30, 2018
- Accepted: January 2, 2019
- Accepted Manuscript published: January 10, 2019 (version 1)
- Version of Record published: January 22, 2019 (version 2)
- Version of Record updated: January 23, 2019 (version 3)
© 2019, Miller et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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