The small protein MgtS and small RNA MgrR modulate the PitA phosphate symporter to boost intracellular magnesium levels

Abstract

Summary In response to low levels of magnesium (Mg2+), the PhoQP two component system induces the transcription of two convergent genes, one encoding a 31-amino acid protein denoted MgtS and the second encoding a small, regulatory RNA (sRNA) denoted MgrR. Previous studies showed that the MgtS protein interacts with and stabilizes the MgtA Mg2+ importer to increase intracellular Mg2+ levels, while the MgrR sRNA base pairs with the eptB mRNA thus affecting lipopolysaccharide modification. Surprisingly, we found overexpression of the MgtS protein also leads to induction of the PhoRB regulon. Studies to understand this activation showed that MgtS forms a complex with a second protein, PitA, a cation-phosphate symporter. Given that the additive effect of ΔmgtA and ΔmgtS mutations on intracellular Mg2+ concentrations seen previously is lost in the ΔpitA mutant, we suggest that MgtS binds to and prevents Mg2+ leakage through PitA under Mg2+-limiting conditions. Consistent with a detrimental role of PitA in low Mg2+, we also observe MgrR sRNA repression of PitA synthesis. Thus, PhoQP induces the expression of two convergent small genes in response to Mg2+ limitation whose products act to modulate PitA at different levels to increase intracellular Mg2+.

The Small RNA PinT Contributes to PhoP-Mediated Regulation of the Salmonella Pathogenicity Island 1 Type III Secretion System in Salmonella enterica Serovar Typhimurium

“…We have shown that the PhoP represses hilA transcription by blocking activation of the promoter and also indirectly affects hilD and rtsA transcription, providing mechanistic insight into how the SPI1 system is shut off after invasion (60). PhoPQ also induces two sRNAs: MgrR and PinT (33,61,62). MgrR regulates genes involved in lipopolysaccharide modification and phosphate import in response to intracellular magnesium levels (61)(62)(63).…”

“…PhoPQ also induces two sRNAs: MgrR and PinT (33,61,62). MgrR regulates genes involved in lipopolysaccharide modification and phosphate import in response to intracellular magnesium levels (61)(62)(63). The 80-nucleotide (nt) sRNA PinT is produced as a primary transcript, is induced in intracellular Salmonella, and regulates virulence-associated genes (33,44).…”

Identifying small proteins by ribosome profiling with stalled initiation complexes

“…These regulators have been identified in organisms spanning the phylogenetic tree of life, and important roles have been characterized for small proteins in bacteria and eukaryotes. In Escherichia coli, for example, the absence of the 49 amino acid protein AcrZ renders cells more susceptible to specific antibiotics (4), and cells lacking the 31 amino acid protein MgtS are sensitive to low magnesium concentrations (5,6). In humans and other mammals, the small proteins myoregulin, sarcolipin, and phospholamban regulate muscle activity by affecting calcium transport (7,8).…”

Small open reading frames and cellular stress responses

“…29 This membranebound SEP also interacts with the PitA cation-phosphate transporter to prevent Mg 2+ export. 47 In contrast, accumulation of Mn 2+ can be toxic to cells. 48 The SEP MntS is repressed by the manganese-dependent transcriptional regulator MntR at high manganese, and overexpression of MntS leads to increased manganese sensitivity.…”