Abstract
Cells employ specific and nonspecific mechanisms to protect their genome integrity against exogenous and endogenous factors. The clbS gene is part of the polyketide synthase machinery (pks genomic island) encoding colibactin, a genotoxin implicated in promoting colorectal cancer. The pks is found among the Enterobacteriaceae, in particular Escherichia coli strains of the B2 phylogenetic group. Several resistance mechanisms protect toxin producers against toxicity of their products. ClbS, a cyclopropane hydrolase, was shown to confer colibactin resistance by opening its electrophilic cyclopropane ring. Here we report that ClbS sustained viability and enabled growth also of E. coli expressing another genotoxin, the Usp nuclease. The recA::gfp reporter system showed that ClbS protects against Usp induced DNA damage. To elucidate the mechanism of ClbS mediated protection, we studied the DNA binding ability of the ClbS protein. We show that ClbS directly interacts with single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA), whereas ssDNA seems to be the preferred substrate. Thus, the ClbS DNA-binding characteristics may serve bacteria to protect their genomes against DNA degradation.
Highlights
To protect the integrity of their genomes against exogenous and endogenous assault, cells employ specific and as well as nonspecific mechanisms
As we previously demonstrated that immunity to the Usp genotoxin is assured by the Imu3 protein via nonspecific DNA binding [16], we postulated that ClbS might provide direct genome protection
Our results show that ClbS is a multifunctional protein, that besides directly inactivating colibactin, as shown previously, associates with DNA to presumably protect the genome against certain genotoxic agents
Summary
To protect the integrity of their genomes against exogenous and endogenous assault, cells employ specific and as well as nonspecific mechanisms. Chemical agents and others, while endogenous factors are reactive oxygen species, metabolic products [1] and in a number of bacterial species potentially genotoxins. Genotoxins such as colibactin are significant bacterial virulence factors that provoke DNA damage in eukaryotic cells. As we previously demonstrated that immunity to the Usp genotoxin is assured by the Imu protein via nonspecific DNA binding [16], we postulated that ClbS might provide direct genome protection. Our results show that ClbS is a multifunctional protein, that besides directly inactivating colibactin, as shown previously, associates with DNA to presumably protect the genome against certain genotoxic agents
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