Taxonomic distribution of proteins containing MgtE_N domains

The tree below includes only several representative species and genera. The complete taxonomic breakdown of all proteins containing MgtE_N domains can be accessed here. Click the counts or percentage values to display the corresponding proteins.

Crystal structure of the MgtE Mg2+ transporter.

Hattori M, Tanaka Y, Fukai S, Ishitani R, Nureki O
Nature. 2007; 448: 1072-5

The magnesium ion Mg2+ is a vital element involved in numerousphysiological processes. Mg2+ has the largest hydrated radius among allcations, whereas its ionic radius is the smallest. It remains obscure howMg2+ transporters selectively recognize and dehydrate the large, fullyhydrated Mg2+ cation for transport. Recently the crystal structures of theCorA Mg2+ transporter were reported. The MgtE family of Mg2+ transportersis ubiquitously distributed in all phylogenetic domains, and humanhomologues have been functionally characterized and suggested to beinvolved in magnesium homeostasis. However, the MgtE transporters have notbeen thoroughly characterized. Here we determine the crystal structures ofthe full-length Thermus thermophilus MgtE at 3.5 A resolution, and of thecytosolic domain in the presence and absence of Mg2+ at 2.3 A and 3.9 Aresolutions, respectively. The transporter adopts a homodimericarchitecture, consisting of the carboxy-terminal five transmembranedomains and the amino-terminal cytosolic domains, which are composed ofthe superhelical N domain and tandemly repeatedcystathionine-beta-synthase domains. A solvent-accessible pore nearlytraverses the transmembrane domains, with one potential Mg2+ bound to theconserved Asp 432 within the pore. The transmembrane (TM)5 helices fromboth subunits close the pore through interactions with the 'connectinghelices', which connect the cystathionine-beta-synthase and transmembranedomains. Four putative Mg2+ ions are bound at the interface between theconnecting helices and the other domains, and this may lock the closedconformation of the pore. A structural comparison of the two states of thecytosolic domains showed the Mg2+-dependent movement of the connectinghelices, which might reorganize the transmembrane helices to open thepore. These findings suggest a homeostasis mechanism, in which Mg2+ boundbetween cytosolic domains regulates Mg2+ flux by sensing the intracellularMg2+ concentration. Whether this presumed regulation controls gating of anion channel or opening of a secondary active transporter remains to bedetermined.