Increasing intracellular magnesium levels with the 31-amino acid MgtS protein

Synthesis of the 31-amino acid, inner membrane protein MgtS (formerly denoted YneM) is induced by very low Mg2+ in a PhoPQdependent manner in Escherichia coli. Here we report that MgtS acts to increase intracellular Mg2+ levels and maintain cell integrity upon Mg2+ depletion. Upon development of a functional tagged derivative of MgtS, we found that MgtS interacts with MgtA to increase the levels of this P-type ATPase Mg2+ transporter under Mg2+-limiting conditions. Correspondingly, the effects of MgtS upon Mg2+ limitation are lost in a Delta mgtA mutant, and MgtA overexpression can suppress the Delta mgtS phenotype. MgtS stabilization of MgtA provides an additional layer of regulation of this tightly controlled Mg2+ transporter and adds to the list of small proteins that regulate inner membrane transporters.