Cryo-EM Structures of the Magnesium Channel CorA Reveal Symmetry Break upon Gating

Doreen Matthies, Olivier Dalmas, Mario J. Borgnia, Pawel K. Dominik, Alan Merk, Prashant Rao, Bharat G. Reddy, Shahidul Islam, Alberto Bartesaghi, Eduardo Perozo, Sriram Subramaniam

Research output: Contribution to journalArticlepeer-review

Abstract

CorA, the major Mg2+ uptake system in prokaryotes, is gated by intracellular Mg2+ (KD ∼1-2 mM). X-ray crystallographic studies of CorA show similar conformations under Mg2+-bound and Mg2+-free conditions, but EPR spectroscopic studies reveal large Mg2+-driven quaternary conformational changes. Here, we determined cryo-EM structures of CorA in the Mg2+-bound closed conformation and in two open Mg2+-free states at resolutions of 3.8, 7.1, and 7.1 Å, respectively. In the absence of bound Mg2+, four of the five subunits are displaced to variable extents (∼10-25 Å) by hinge-like motions as large as ∼35° at the stalk helix. The transition between a single 5-fold symmetric closed state and an ensemble of low Mg2+, open, asymmetric conformational states is, thus, the key structural signature of CorA gating. This mechanism is likely to apply to other structurally similar divalent ion channels.

Original languageEnglish (US)
Pages (from-to)747-756
Number of pages10
JournalCell
Volume164
Issue number4
DOIs
StatePublished - Feb 11 2016
Externally publishedYes

Keywords

  • asymmetry
  • conformational change
  • direct electron detector
  • ion channel
  • membrane protein structure
  • single-particle cryo-electron microscopy

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)

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