Helicase family proteins promote antiviral ADP-ribosylation of DNA purines

Griesman, T.; Arifah, A. Q.; Tomko, E. J.; Tan, Y.; Tsao, N.; Trotter, J. T.; Khochare, S. S.; Carlson, N. A.; Mosammaparast, N.; Zhang, D.; Galburt, E. A.; Patinios, C.; LeRoux, M.

doi:10.64898/2026.11.02.763693

bioRxiv · 10.64898/2026.11.02.763693

Helicase family proteins promote antiviral ADP-ribosylation of DNA purines

Griesman, T.·Arifah, A. Q.·Tomko, E. J.·Tan, Y.·Tsao, N.·Trotter, J. T.·Khochare, S. S.·Carlson, N. A.·Mosammaparast, N.·Zhang, D.·Galburt, E. A.·Patinios, C.·LeRoux, M.

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Abstract

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 Escherichia coli DarHTG3 system confers broad phage defense, requires DarH and, unlike previously characterized DarTG systems, modifies adenine. Characterization of additional DarH-containing DarTG systems reveals that a subset also target guanine. Our data support a model in which ADP-bound DarH functions as a processivity factor by recruiting DarT to its single-stranded DNA substrate and allowing for ADP-ribosylation of multiple target sites. These findings reveal how a helicase family protein regulates an antiviral effector by promoting DNA engagement rather than unwinding and thereby expanding the functional repertoire of helicase family proteins in bacterial immunity.

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Griesman, T., Arifah, A. Q., Tomko, E. J., Tan, Y., Tsao, N., Trotter, J. T., Khochare, S. S., Carlson, N. A., Mosammaparast, N., Zhang, D., Galburt, E. A., Patinios, C., LeRoux, M.. 2026-11-03. Helicase family proteins promote antiviral ADP-ribosylation of DNA purines. https://doi.org/10.64898/2026.11.02.763693

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