Dear Colleagues,

ADP-ribosylation is a reversible post-translational modification defined by adding ADP-ribose moieties from NAD+ to the target. ADP-ribosylaton is widely used post-trans-modifications in all kingdoms of life. The system likely originated in bacteria, which functions in inter- and intra-species signalling, and stress response. At first, as bacterial toxins, it was found that cholera toxin ADP-ribosylates a specific arginine in the Gsa of heteromeric G-proteins, and the diphtheria toxin ADP-ribosdylates the eukaryotic elongation factor 2 (eEF2). Later, the ARTC and ARTD families were named because they are characterized by a catalytic domain fold related to cholera toxin or diphtheria toxin, respectively. For understanding mammalian ADP-ribosylation systems, these classifications were used. Later, other toxins such as C3 exoenzyme and C2 toxin were found to ADP-ribosylate RhoA and actin, respectively. These canonical bacterial toxins studies could give us basic knowledge of ADP-ribosylation.

On the other hand, recent studies opened the non-canonical ADP-ribosylation system. (1) DNA ADP-ribosylation: The target of ADP-ribosylation is not only protein but also nucleic acids, DNA. For example, pierisin found in cabbage butterflies was shown to modify DNA. Its related enzyme Streptomyces coelicolor　ScARP ADP-ribosylates GDP. Following, reversible ADP-ribosylation of DNA on thymidine bases occurs through the DarT-DarG toxin-antitoxin system, which is found in a variety of bacteria, including such as Mycobacterium tuberculosis, enteropathogenic Escherichia coli and Pseudomonas aeruginosa. (2) Ubiquitination via ADP-ribosylations: Legionella pneumophila SidE effector ubiquitylates serine residues in substrate via an ADP-ribosylated ubiquitin intermediate without E1 and E2 enzymes. (3) ADP-riboxanation: The type III secretion system effector of Shigella flexneri, OspC3, ADP-ribosylates the caspase and then followed by non-enzymatic deamidation.

In addition to a basic understanding of canonical ADP-ribosylation, studies of non-canonical ADP-ribosylation would benefit an understanding of deep ADP ribosylation systems. Therefore, we are calling for the community to submit original research articles or reviews on elucidating the role of ADP-ribosylation, including both canonical and non-canonical ADP-ribosylation systems. The target includes not only bacterial enzymes but also plant, insect and virus enzymes.

Prof. Dr. Hideaki Tsuge
Guest Editor

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• canonical ADP-ribosylation
• non-canonical ADP-ribosylation
• ubiquitination
• DNA ADP-ribosylation
• ADP-riboxanation