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.
- 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)