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

Cell. 2016 Feb 11;164(4):747-56. doi: 10.1016/j.cell.2015.12.055.


CorA, the major Mg(2+) uptake system in prokaryotes, is gated by intracellular Mg(2+) (KD ∼ 1-2 mM). X-ray crystallographic studies of CorA show similar conformations under Mg(2+)-bound and Mg(2+)-free conditions, but EPR spectroscopic studies reveal large Mg(2+)-driven quaternary conformational changes. Here, we determined cryo-EM structures of CorA in the Mg(2+)-bound closed conformation and in two open Mg(2+)-free states at resolutions of 3.8, 7.1, and 7.1 Å, respectively. In the absence of bound Mg(2+), 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 Mg(2+), 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.

Keywords: asymmetry; conformational change; direct electron detector; ion channel; membrane protein structure; single-particle cryo-electron microscopy.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Bacterial Proteins / chemistry
  • Bacterial Proteins / ultrastructure*
  • Cation Transport Proteins / chemistry
  • Cation Transport Proteins / ultrastructure*
  • Cryoelectron Microscopy
  • Magnesium / metabolism*
  • Models, Molecular
  • Molecular Dynamics Simulation
  • Thermotoga maritima / chemistry*


  • Bacterial Proteins
  • Cation Transport Proteins
  • Magnesium