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Molecular basis for DarT ADP-ribosylation of a DNA base

Schuller, Marion; Butler, Rachel; Ariza, Antonio; Tromans-Coia, Callum; Jankevicius, Gytis; Claridge, Tim; Kendall, Sharon; Goh, Shan; Stewart, Graham; Ahel, Ivan


Marion Schuller

Rachel Butler

Antonio Ariza

Callum Tromans-Coia

Gytis Jankevicius

Tim Claridge

Sharon Kendall

Shan Goh

Graham Stewart

Ivan Ahel


ADP-ribosyltransferases (ARTs) utilise NAD+ to catalyse substrate ADP-ribosylation, thereby regulating cellular pathways or contributing to toxin-mediated pathogenicity of bacteria. Reversible ADP-ribosylation has traditionally been considered a protein-specific modification, but recent in vitro studies have suggested nucleic acids as targets. Here, we present evidence that specific reversible DNA ADP-ribosylation on thymidine bases occurs in cellulo through the DarT/DarG toxin/antitoxin system which is found in a variety of bacteria including global pathogens such as Mycobacterium tuberculosis, EPEC and Pseudomonas aeruginosa. We report the first DarT structure which identifies this protein as a diverged member of the PARP family. Moreover, a set of high-resolution structures in ligand-free, pre-and post-reaction states reveals a specialised mechanism of catalysis that includes a key active-site arginine, extending the canonical ART toolkit. Comparison with the well-established DNA-repair protein ADP-ribosylation complex, PARP/HPF1, offers insights into how the DarT class of ARTs evolved into specific DNA-modifying enzymes. Together, the structural and mechanistic data provide unprecedented detail for a PARP family member and contribute to fundamental understanding of nucleic acid ADP-ribosylation. We furthermore show that thymine-linked ADP-ribose DNA adducts reversed by DarG antitoxin, functioning as non-canonical DNA-repair factor, are utilised not only for targeted DNA damage to induce toxicity but also as a signalling strategy for cellular processes. Using M. tuberculosis as an exemplar we show that DarTG regulates growth by DNA ADP-ribosylation at the origin of chromosome replication


Schuller, M., Butler, R., Ariza, A., Tromans-Coia, C., Jankevicius, G., Claridge, T., …Ahel, I. (2021). Molecular basis for DarT ADP-ribosylation of a DNA base. Nature,

Journal Article Type Article
Acceptance Date Jul 15, 2021
Publication Date Aug 18, 2021
Deposit Date Jul 15, 2021
Publicly Available Date Aug 20, 2021
Print ISSN 0028-0836
Publisher Nature Research
Peer Reviewed Peer Reviewed
Public URL


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