A bacterial toxin inhibits DNA replication elongation through a direct interaction with the β sliding clamp.
Toxin-antitoxin (TA) systems are ubiquitous on bacterial chromosomes, yet the mechanisms regulating their activity and the molecular targets of toxins remain incompletely defined. Here, we identify SocAB, an atypical TA system in Caulobacter crescentus. Unlike canonical TA systems, the toxin SocB is unstable and constitutively degraded by the protease ClpXP; this degradation requires the antitoxin, SocA, as a proteolytic adaptor. We find that the toxin, SocB, blocks replication elongation through an interaction with the sliding clamp, driving replication fork collapse. Mutations that suppress SocB toxicity map to either the hydrophobic cleft on the clamp that binds DNA polymerase III or a clamp-binding motif in SocB. Our findings suggest that SocB disrupts replication by outcompeting other clamp-binding proteins. Collectively, our results expand the diversity of mechanisms employed by TA systems to regulate toxin activity and inhibit bacterial growth, and they suggest that inhibiting clamp function may be a generalizable antibacterial strategy.
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Christopher D
CD
Aakre
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Tuyen N
TN
Phung
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
David
D
Huang
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. Electronic address: laub@mit.edu.
Michael T
MT
Laub
D000992:Antitoxins / Q000235:genetics* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001427:Bacterial Toxins / Q000235:genetics* / Q000378:metabolism*; D016935:Caulobacter crescentus / Q000235:genetics / Q000378:metabolism; D002876:Chromosomes, Bacterial; D004261:DNA Replication / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D011485:Protein Binding; D059748:Proteolysis
D000992:Antitoxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004268:DNA-Binding Proteins