Du J, et al. (2009) Investigating the ADP-ribosyltransferase activity of sirtuins with NAD analogues and 32P-NAD. Biochemistry 48(13):2878-90
Abstract: 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.
|Status: Published||Type: Journal Article||PubMed ID: 19220062|
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