The MgtR regulatory peptide negatively controls expression of the MgtA Mg2+ transporter in Salmonella enterica serovar Typhimurium

MgtR is a 30 amino acid peptide that is encoded from the mgtCBR operon. This peptide has recently been demonstrated to interact with the MgtC virulence protein and lead to MgtC degradation. In the present study, we reveal that the MgtA Mg2+ transporter is another protein under the direct control of the MgtR peptide. Salmonella expresses the MgtA transporter only in Mg2+ depleted conditions. We determined that the mgtR peptide limits levels of the MgtA protein at low Mg2+ concentrations. MgtA expression increased in a Salmonella strain lacking MgtR but decreased in a strain overexpressing MgtR. Moreover, we found that the MgIR peptide is necessary for the MgtA protein to be induced at the normal timing upon Mg2+ starvation. The MgtR peptide did not affect transcription of the mgtA gene but specifically bound to the MgtA transporter in vivo, resembling the features of MgtR-regulated MgtC expression. MgtR-mediated regulation of MgtA expression was biologically significant because the lack of MgtR enhanced Salmonella growth in low Mg2+. (C) 2011 Elsevier Inc. All rights reserved.