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

Synthesis of the 31-amino acid, inner membrane protein MgtS (formerly denoted YneM) is induced by very low Mg²⁺ in a PhoPQ-dependent 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 ∆mgtA mutant, and MgtA overexpression can suppress the ∆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.