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XB-ART-48917
Proc Natl Acad Sci U S A 2014 Feb 25;1118:3002-7. doi: 10.1073/pnas.1319054111.
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A repulsion mechanism explains magnesium permeation and selectivity in CorA.

Dalmas O , Sandtner W , Medovoy D , Frezza L , Bezanilla F , Perozo E .


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Magnesium (Mg(2+)) plays a central role in biology, regulating the activity of many enzymes and stabilizing the structure of key macromolecules. In bacteria, CorA is the primary source of Mg(2+) uptake and is self-regulated by intracellular Mg(2+). Using a gating mutant at the divalent ion binding site, we were able to characterize CorA selectivity and permeation properties to both monovalent and divalent cations under perfused two-electrode voltage clamp. The present data demonstrate that under physiological conditions, CorA is a multioccupancy Mg(2+)-selective channel, fully excluding monovalent cations, and Ca(2+), whereas in absence of Mg(2+), CorA is essentially nonselective, displaying only mild preference against other divalents (Ca(2+) > Mn(2+) > Co(2+) > Mg(2+) > Ni(2)(+)). Selectivity against monovalent cations takes place via Mg(2+) binding at a high-affinity site, formed by the Gly-Met-Asn signature sequence (Gly312 and Asn314) at the extracellular side of the pore. This mechanism is reminiscent of repulsion models proposed for Ca(2+) channel selectivity despite differences in sequence and overall structure.

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References [+] :
Adams, The permeability of endplate channels to monovalent and divalent metal cations. 1980, Pubmed