The MgrB protein is a short lipoprotein. The mgrB gene has a mg2+ responsive promoter [1]. Deletion of mgrB results in a potent increase in PhoP-regulated transcription [3]. The PhoQ/PhoP signaling system responds to low magnesium and the presence of certain cationic antimicrobial peptides. Over-expression of mgrB decreased transcription at both high and low concentrations of magnesium. Localization and bacterial two-hybrid studies suggest that MgrB resides in the inner-membrane and interacts directly with PhoQ. This domain family is found in bacteria, and is approximately 40 amino acids in length. There are two conserved sequence motifs: CDQ and GIC.

1: Molecular characterization of the PhoP-PhoQ two-component system in Escherichia coli K-12: identification of extracellular Mg2+-responsive promoters. Kato A, Tanabe H, Utsumi R; J Bacteriol. 1999;181:5516-5520. PMID:10464230

2: Stimulus-dependent differential regulation in the Escherichia coli PhoQ PhoP system. Miyashiro T, Goulian M; Proc Natl Acad Sci U S A. 2007;104:16305-16310. PMID:17909183

3: Feedback inhibition in the PhoQ/PhoP signaling system by a membrane peptide. Lippa AM, Goulian M; PLoS Genet. 2009;5:e1000788. PMID:20041203