Helicase family proteins promote antiviral ADP-ribosylation of DNA purines
DarTG defense systems studied to date contain a DarT1 or DarT2 toxin that blocks phage replication by ADP-ribosylating DNA and a NADAR or macrodomain antitoxin, DarG, that reverses this modification at homeostasis. Here, we identify additional DarTG subfamilies, one of which comprises a DarT3 toxin, an ADP-ribosylhydrolase (ARH)-domain antitoxin, and a helicase family protein, DarH. The…
Researchers have discovered a new subfamily of DarTG defense systems that utilize helicase family proteins to promote antiviral ADP-ribosylation of DNA purines. These systems contain a DarT3 toxin, an ADP-ribosylhydrolase (ARH)-domain antitoxin, and a helicase family protein. The Escherichia coli DarHTG3 system is one such example, which requires DarH and modifies adenine in a way that is distinct from previously identified DarTG systems.
By characterizing additional DarH-containing DarTG systems, researchers have found that some of these systems target both adenine and guanine. The data suggest that ADP-bound DarH functions as a processivity factor, recruiting DarT to the single-stranded DNA substrate and enabling ADP-ribosylation of multiple target sites. This new understanding of how helicase family proteins regulate antiviral effector mechanisms expands the functional repertoire of these proteins in bacterial immunity.
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