A widespread bacteriophage abortive infection system functions through a Type IV toxin-antitoxin mechanism.
Bacterial abortive infection (Abi) systems are 'altruistic' cell death systems that are activated by phage infection and limit viral replication, thereby providing protection to the bacterial population. Here, we have used a novel approach of screening Abi systems as a tool to identify and characterize toxin-antitoxin (TA)-acting Abi systems. We show that AbiE systems are encoded by bicistronic operons and function via a non-interacting (Type IV) bacteriostatic TA mechanism. The abiE operon was negatively autoregulated by the antitoxin, AbiEi, a member of a widespread family of putative transcriptional regulators. AbiEi has an N-terminal winged-helix-turn-helix domain that is required for repression of abiE transcription, and an uncharacterized bi-functional C-terminal domain, which is necessary for transcriptional repression and sufficient for toxin neutralization. The cognate toxin, AbiEii, is a predicted nucleotidyltransferase (NTase) and member of the DNA polymerase β family. AbiEii specifically bound GTP, and mutations in conserved NTase motifs (I-III) and a newly identified motif (IV), abolished GTP binding and subsequent toxicity. The AbiE systems can provide phage resistance and enable stabilization of mobile genetic elements, such as plasmids. Our study reveals molecular insights into the regulation and function of the widespread bi-functional AbiE Abi-TA systems and the biochemical properties of both toxin and antitoxin proteins.
Department of Microbiology and Immunology, University of Otago, 720 Cumberland Street, PO Box 56, Dunedin 9054, New Zealand and Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QW, UK.
Ron L
RL
Dy
Rita
R
Przybilski
Koen
K
Semeijn
George P C
GP
Salmond
Peter C
PC
Fineran
D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism*; D001435:Bacteriophages / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D016680:Genome, Bacterial; D006160:Guanosine Triphosphate / Q000378:metabolism; D055029:Inverted Repeat Sequences; D013294:Lactococcus lactis / Q000235:genetics; D009154:Mutation; D009713:Nucleotidyltransferases / Q000145:classification; D010957:Plasmids / Q000502:physiology; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013292:Streptococcus agalactiae / Q000235:genetics
D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004268:DNA-Binding Proteins; D012097:Repressor Proteins; D006160:Guanosine Triphosphate; D009713:Nucleotidyltransferases