Mg2+-dependent gating of bacterial MgtE channel underlies Mg2+ homeostasis

The MgtE family of Mg2+ transporters is ubiquitously distributed in all phylogenetic domains. Recent crystal structures of the full-length MgtE and of its cytosolic domain in the presence and absence of Mg2+ suggested a Mg2+-homeostasis mechanism, in which the MgtE cytosolic domain acts as a 'Mg2+ sensor' to regulate the gating of the ion-conducting pore in response to the intracellular Mg2+ concentration. However, complementary functional analyses to confirm the proposed model have been lacking. Moreover, the limited resolution of the full-length structure precluded an unambiguous characterization of these regulatory divalent-cation-binding sites. Here, we showed that MgtE is a highly Mg2+-selective channel gated by Mg2+ and elucidated the Mg2+-dependent gating mechanism of MgtE, using X-ray crystallographic, genetic, biochemical, and electrophysiological analyses. These structural and functional results have clarified the control of Mg2+ homeostasis through cooperative Mg2+ binding to the MgtE cytosolic domain. The EMBO Journal (2009) 28, 3602-3612. doi:10.1038/emboj.2009.288; Published online 1 October 2009