Proteotoxic Stress Induces a Cell-Cycle Arrest by Stimulating Lon to Degrade the Replication Initiator DnaA

Abstract

Summary The decision to initiate DNA replication is a critical step in the cell cycle of all organisms. Cells often delay replication in the face of stressful conditions, but the underlying mechanisms remain incompletely defined. Here, we demonstrate in Caulobacter crescentus that proteotoxic stress induces a cell cycle arrest by triggering the degradation of DnaA, the conserved replication initiator. A depletion of available Hsp70 chaperone, DnaK, either through genetic manipulation or heat shock, induces synthesis of the Lon protease, which can directly degrade DnaA. Unexpectedly, we find that unfolded proteins, which accumulate following a loss of DnaK, also allosterically activate Lon to degrade DnaA, thereby ensuring a cell cycle arrest. Our work reveals a new mechanism for regulating DNA replication under adverse growth conditions. Additionally, our data indicate that unfolded proteins can actively and directly alter substrate recognition by cellular proteases.

Adaptor-mediated Lon proteolysis restrictsBacillus subtilishyperflagellation

“…Consistent with an adaptor function, SmiA facilitates Londependent proteolysis of SwrA both in vivo and in vitro. Unlike known allosteric activators of Lon, such as unfolded protein substrates, SmiA does not simply enhance general proteolytic activity, as the presence of SmiA did not accelerate the LonAdependent degradation of α-casein or titin (13,16,44). Further, SmiA did not function as a generalized unfolding chaperone, as SmiA did not promote SwrA proteolysis by the heterologous Lon protease from E. coli.…”

“…SmiA could enhance SwrA degradation either as an adaptor for specific SwrA proteolysis or as an allosteric activator of generalized protease activity (7,13,16). Unfolded proteins have been proposed to be both substrates and allosteric Lon activators but the presence and degradation of α-casein did not promote proteolysis of SwrA ( Fig.…”

“…Lon is thought to degrade misfolded proteins by recognizing hydrophobic peptide sequences known as degrons that are normally buried in the hydrophobic core of folded proteins and become solvent exposed upon protein misfolding (12,13). Lon is also known to conduct regulatory proteolysis by highly specific degradation of key cellular regulators but to date, little has been reported regarding Lon-specific adaptor proteins (10,(14)(15)(16)(17). Thus, if and how Lon distinguishes specific regulatory targets from general misfolded proteins is an open question.…”

Response of single bacterial cells to stress gives rise to complex history dependence at the population level

“…S6). One possible molecular mechanism for the delay in cell division that leads to synchronization has been established by previous work: In C. crescentus, exposure to diverse stressors leads to the degradation of the essential replication initiation factor DnaA (25)(26)(27) by the Lon protease. It is possible that DnaA degradation in response to exposure to sodium chloride induced a halt in the cell-division cycle that led to synchronization.…”

Host plant peptides elicit a transcriptional response to control theSinorhizobium meliloticell cycle during symbiosis

“…One possibility is that NCR247 simply inhibits the formation, stability, or function of the Z-ring or other components of the cell-division machinery, as found for other small proteins that regulate bacterial cell division (17,18). A second possibility is that NCR247-peptide treatment blocks cell division by eliciting responses that disrupt cell-cycle regulatory pathways, as has been found to occur in Caulobacter crescentus cells in response to certain stresses (19,20).…”