Sequestration from Protease Adaptor Confers Differential Stability to Protease Substrate

Abstract

Summary According to the N-end rule, the N-terminal residue of a protein determines its stability. In bacteria, the adaptor ClpS mediates proteolysis by delivering substrates bearing specific N-terminal residues to the protease ClpAP. We now report that the Salmonella adaptor ClpS binds to the N-terminus of the regulatory protein PhoP, resulting in PhoP degradation by ClpAP. We establish that the PhoP-activated protein MgtC protects PhoP from degradation by outcompeting ClpS for binding to PhoP. MgtC appears to act exclusively on PhoP as it did not alter the stability of a different ClpS-dependent ClpAP substrate. Removal of five N-terminal residues rendered PhoP stability independent of both the clpS and mgtC genes. By preserving PhoP protein levels, MgtC enables normal temporal transcription of PhoP-activated genes. The identified mechanism provides a simple means to spare specific substrates from an adaptor-dependent protease.

ATP reduction by MgtC and Mg2+ homeostasis by MgtA and MgtB enables Salmonella to accumulate RpoS upon low cytoplasmic Mg2+ stress

“…B). Consistent with the previous finding that cytoplasmic Mg 2+ starvation triggers mgtC expression (Spinelli et al , ; Yeom et al , ), MgtC levels greatly increased at 4 h, when Salmonella typically enters the slow‐growth phase (Fig. A), and remained constant for the following 8 h (Fig.…”

High‐level, constitutive expression of the mgtC gene confers increased thermotolerance on Salmonella enterica serovar Typhimurium

“…Our observations suggest that the complex functions of MgtC include regulation of thermotolerance in addition to its role in the regulation of virulence (Blanc‐Potard and Groisman, ), growth and flagella‐independent motility at low Mg 2+ concentrations, and the production of cellulose (Pontes et al ., ) and succinic acid (Wang et al ., ). The observation that MgtC can protect PhoP from proteolysis (Yeom et al ., ) raises the possibility that overproduction of MgtC could increase the steady state level of PhoP, and the enhanced thermotolerance in the mgtM mutants might be the consequence of overproduction of protein(s) in the PhoQP regulon.…”

“…The issue of what environmental factors regulate PhoQ is controversial (Papp‐Wallace and Maguire, ): activating signals that have been proposed are some antimicrobial peptides (Bader et al ., ), acid pH (Alpuche Aranda et al ., ), osmotic stress (Yuan et al ., ) and low extracellular [Mg 2+ ] (Groisman, ). Recently, it was reported that MgtC interacts with PhoP to protect the latter protein from degradation by the ClpS/ClpAP protease (Yeom et al ., ).…”

Activation of master virulence regulator PhoP in acidic pH requires the Salmonella -specific protein UgtL

“…S7). That a given protein may have more than one target is also illustrated by another PhoP-activated protein, MgtC, which binds to and inhibits the F 1 F o ATP synthase (55) and binds to and stabilizes PhoP (56). …”