The small membrane protein MgrB regulates PhoQ bifunctionality to control PhoP target gene expression dynamics

Abstract

In Escherichia coli and other γ-proteobacteria, the PhoQ-PhoP two-component signaling system responds to low extracellular Mg and cationic antimicrobial peptides. On transition to inducing conditions, the expression of PhoP-dependent genes increases rapidly, but then decays to a new, intermediate steady-state level, a phenomenon often referred to as partial adaptation. The molecular basis for this partial adaptation has been unclear. Here, using time-lapse fluorescence microscopy to examine PhoP-dependent gene expression in individual E. coli cells we show that partial adaptation arises through a negative feedback loop involving the small protein MgrB. When E. coli cells are shifted to low Mg , PhoQ engages in multiple rounds of autophosphorylation and phosphotransfer to PhoP, which, in turn, drives the expression of mgrB. MgrB then feeds back to inhibit the kinase activity of PhoQ. PhoQ is bifunctional such that, when not active as a kinase, it can stimulate the dephosphorylation of PhoP. Thus, MgrB drives the inactivation of PhoP and the observed adaptation in PhoP-dependent gene expression. Our results clarify the source of feedback inhibition in the E. coli PhoQ-PhoP system and reveal how exogenous factors, such as MgrB, can combine with a canonical two-component signaling pathway to produce complex temporal dynamics in target gene expression.

Asymmetric regulation of quorum-sensing receptors drives autoinducer-specific gene expression programs in Vibrio cholerae

“…cholerae QS response (Fig 5B). Thus, the asymmetry in CAI-1 response that we discovered stems exclusively from positive feedback on CqsS which changes the stoichiometry of the two major QS receptors [49–53]. Biasing the system to favor the intra-genus CAI-1 autoinducer at HCD could be a type of kin-discrimination, ensuring that expensive public goods are not produced until sufficient numbers of kin are present [54].…”

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

“…In E. coli , the PhoQP system upregulates two small membrane proteins, MgrB and MgtS, to affect Mg 2+ homeostasis (Lippa and Goulian, , Wang et al ., ). MgrB interacts with the sensor kinase PhoQ to repress autophosphorylation, resulting in feedback inhibition that modulates PhoP target gene expression (Salazar et al ., ). MgtS stabilizes the Mg 2+ transporter MgtA to increase Mg 2+ import.…”

Quantitative Kinetic Analyses of Shutting Off a Two-Component System

“…A small extent of overshoot kinetics, or impulse response (32, 33), was observed for RU1616 but not for the WT strain, with promoter activities reaching a high level before relaxing to the eventual steady state. Impulse responses have been suggested to result from negative feedback in TCS pathways (12, 15, 34), but the reason for the absence of the overshoot kinetics in the WT strain is not clear. Nevertheless, the temporal profile nicely recapitulates the PhoB phosphorylation kinetics in vivo (Fig.…”

“…Most studies have been focused on the static ON (high level of RR phosphorylation) and OFF (low level of RR phosphorylation) states of the pathway, and TCSs are often portrayed as simple switches that can toggle between these static states. Several studies have begun to explore the sophisticated control that TCS pathways can exert on signaling dynamics, with many focusing on system activation (10–15). However, it is also of great interest to understand the temporal dynamics of shutting off the pathway.…”