Mg 2-dependent gating of bacterial MgtE channel underlies Mg 2 homeostasis

Abstract

The MgtE family of Mg 2 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 Mg 2 suggested a Mg 2-homeostasis mechanism, in which the MgtE cytosolic domain acts as a Mg 2 sensor to regulate the gating of the ion-conducting pore in response to the intracellular Mg 2 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 Mg 2-selective channel gated by Mg 2 and elucidated the Mg 2-dependent gating mechanism of MgtE, using X-ray crystallographic, genetic, biochemical, and electrophysiological analyses. These structural and functional results have clarified the control of Mg 2 homeostasis through cooperative Mg 2 binding to the MgtE cytosolic domain. © 2009 European Molecular Biology Organization | All Rights Reserved.