A cis‐acting antitoxin domain within the chromosomal toxin–antitoxin module EzeT of Escherichia coli quenches toxin activity

Abstract

SummaryToxin-antitoxin (TA) systems are widespread genetic modules in the genomes of bacteria and archaea emerging as key players that modulate bacterial physiology. They consist of two parts, a toxic component that blocks an essential cellular process and an antitoxin that inhibits this toxic activity during normal growth. According to the nature of the antitoxin and the mode of inhibition, TA systems are subdivided into different types. Here, we describe the characterization of a type II-like TA system in Escherichia coli called EzeT. While in conventional type II systems the antitoxin is expressed in trans to form an inactive proteinprotein complex, EzeT consists of two domains combining toxin and cis-acting antitoxin functionalities in a single polypeptide chain. We show that the C-terminal domain of EzeT is homologous to zeta toxins and is toxic in vivo. The lytic phenotype could be attributed to UDP-N-acetylglucosamine phosphorylation, so far only described for type II epsilon/zeta systems from Gram-positive streptococci. Presence of the N-terminal domain inhibits toxicity in vivo and strongly attenuates kinase activity. Autoinhibition by a cis-acting antitoxin as described here for EzeT-type TA systems can explain the occurrence of single or unusually large toxins, further expanding our understanding of the TA system network.

The toxin GraT inhibits ribosome biogenesis

“…At 25°C, colony formation of the Δ graA strain is severely delayed and no colonies form on solid medium at 20°C (Tamman et al ., ). Interestingly, temperature‐dependent effects are rarely described for TA toxins, with HipA (Scherrer and Moyed, ) and EzeT (Rocker and Meinhart, ) being notable exceptions of toxins that can cause cold sensitivity. However, in the case of HipA, this phenotype is actually caused by specific mutations in the hipA7 allele and no cold sensitivity was recorded for the wild‐type HipA (Korch et al ., ).…”

“…However, in the case of HipA, this phenotype is actually caused by specific mutations in the hipA7 allele and no cold sensitivity was recorded for the wild‐type HipA (Korch et al ., ). EzeT is a fascinating TA protein that contains the toxin and antitoxin activities in a single polypeptide and likely causes cold‐sensitive growth due to its own low thermostability that renders the toxin inactive at optimal growth temperatures (Rocker and Meinhart, ).…”

Toxin YafQ Reduces Escherichia coli Growth at Low Temperatures

“…Therefore, the YafQ/DinJ TA system seems to be utilized primarily at low temperatures in a manner similar to the activation at low temperatures of toxin GraT of the type II GraT/GraA TA system of Pseudomonas putida [42]; toxin GraT inhibits ribosome assembly at low temperatures by interacting with the chaperone DnaK [55]. The other TA systems that are affected by temperature changes are the type I BsrG/SR4 TA system of Bacillus subtilis [41] in which toxin BsrG mRNA is degraded upon heat shock, and the single polypeptide toxin and antitoxin EzeT which only has toxicity at low temperatures due to changes in protein folding [43]. …”

Identification and functional characterization of a bacterial homologue of Zeta toxin in Leishmania donovani

“…Existence of these systems was earlier reported as episomal genetic elements meant to enhance plasmid stability by postsegregational killing, but later their presence was also detected on chromosomes for preservation of transposable elements [8,9]. Existence of these systems was earlier reported as episomal genetic elements meant to enhance plasmid stability by postsegregational killing, but later their presence was also detected on chromosomes for preservation of transposable elements [8,9].…”

“…TA system loci of prokaryotes are bicistronic operons that encodes for stable proteinaceous toxin and unstable neutralizing protein or small RNA as antitoxin. Existence of these systems was earlier reported as episomal genetic elements meant to enhance plasmid stability by postsegregational killing, but later their presence was also detected on chromosomes for preservation of transposable elements [8,9]. Additional functions assigned to TA module include prevalence of persister cells, stress response, protection from phage, regulation of biofilm formation, and virulence.…”