Structural and functional characterization of the bestrophin-2 anion channel

Nat Struct Mol Biol. 2020 Apr;27(4):382-391. doi: 10.1038/s41594-020-0402-z. Epub 2020 Apr 6.

Abstract

The bestrophin family of calcium (Ca2+)-activated chloride (Cl-) channels, which mediate the influx and efflux of monovalent anions in response to the levels of intracellular Ca2+, comprises four members in mammals (bestrophin 1-4). Here we report cryo-EM structures of bovine bestrophin-2 (bBest2) bound and unbound by Ca2+ at 2.4- and 2.2-Å resolution, respectively. The bBest2 structure highlights four previously underappreciated pore-lining residues specifically conserved in Best2 but not in Best1, illustrating the differences between these paralogs. Structure-inspired electrophysiological analysis reveals that, although the channel is sensitive to Ca2+, it has substantial Ca2+-independent activity for Cl-, reflecting the opening at the cytoplasmic restriction of the ion conducting pathway even when Ca2+ is absent. Moreover, the ion selectivity of bBest2 is controlled by multiple residues, including those involved in gating.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Bestrophins / chemistry
  • Bestrophins / genetics
  • Bestrophins / ultrastructure*
  • Calcium / chemistry
  • Cattle
  • Chloride Channels / chemistry
  • Chloride Channels / genetics
  • Chloride Channels / ultrastructure*
  • Cryoelectron Microscopy
  • Cytoplasm / chemistry
  • Cytoplasm / genetics
  • Cytoplasm / ultrastructure
  • Humans
  • Ion Channel Gating / genetics
  • Protein Binding / genetics
  • Protein Conformation*
  • Signal Transduction

Substances

  • BEST1 protein, human
  • Bestrophins
  • Chloride Channels
  • Calcium