Mg2+-sensing mechanism of Mg2+ transporter MgtE probed by molecular dynamics study.

Proper regulation of the intracellular ion concentration is essential to maintain life and is achieved by ion transporters that transport their substrates across the membrane in a strictly regulated manner. MgtE is a Mg(2+) transporter that may function in the homeostasis of the intracellular Mg(2+) concentration. A recent crystallographic study revealed that its cytosolic domain undergoes a Mg(2+)-dependent structural change, which is proposed to gate the ion-conducting pore passing through the transmembrane domain. However, the dynamics of Mg(2+) sensing, i.e., how MgtE responds to the change in the intracellular Mg(2+) concentration, remained elusive. Here we performed molecular dynamics simulations of the MgtE cytosolic domain. The simulations successfully reproduced the structural changes of the cytosolic domain upon binding or releasing Mg(2+), as well as the ion selectivity. These results suggested the roles of the N and CBS domains in the cytosolic domain and their respective Mg(2+) binding sites. Combined with the current crystal structures, we propose an atomically detailed model of Mg(2+) sensing by MgtE.