Protein ADP-ribosyltransferases catalyze the transfer of adenosine diphosphate ribose (ADP-ribose) from nicotinamide adenine dinucleotide (NAD) onto specific target proteins. Sirtuins, a class of enzymes with NAD-dependent deacetylase activity, have been reported to possess ADP-ribosyltransferase activity too. Here we used NAD analogs and <sup>32</sup>P-NAD to study the ADP-ribosyltransferase activity of several different sirtuins, including yeast Sir2, human SirT1, mouse SirT4, and mouse SirT6. The results showed that an alkyne-tagged NAD is substrate for deacetylation reactions, but cannot detect the ADP-ribosylation activity. Furthermore, comparing with a bacterial ADP-ribosyltransferase diphtheria toxin, the observed rate constant of sirtuin-dependent ADP-ribosylation is >5,000 fold lower. Compared with the kcat/Km values of the deacetylation activity of sirtuins, the observed rate constant of sirtuin-dependent ADP-ribosyltion is ~500 times weaker. The weak ADP-ribosylation events can be explained by both enzymatic and non-enzymatic reaction mechanisms. Combined with recent reports on several other sirtuins, we propose that the reported ADP-ribosyltransferase activity of sirtuins is likely some inefficient side reactions of the deacetylase activity and may not be physiologically relevant.
|Evidence ID||Analyze ID||Interactor||Interactor Systematic Name||Interactor||Interactor Systematic Name||Type||Assay||Annotation||Action||Modification||Phenotype||Source||Reference||Note|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Gene Ontology Term||Gene Ontology Term ID||Qualifier||Aspect||Method||Evidence||Source||Assigned On||Annotation Extension||Reference|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Phenotype||Experiment Type||Experiment Type Category||Mutant Information||Strain Background||Chemical||Details||Reference|
|Evidence ID||Analyze ID||Regulator||Regulator Systematic Name||Target||Target Systematic Name||Experiment||Assay||Construct||Conditions||Strain Background||Reference|