Coenzyme specificity of Sir2 protein deacetylases: implications for physiological regulation. J Biol Chem 2004 Sep 17;279(38):40122-9
Date
07/23/2004Pubmed ID
15269219DOI
10.1074/jbc.M407484200Scopus ID
2-s2.0-4544243684 (requires institutional sign-in at Scopus site) 139 CitationsAbstract
Sir2 (silent information regulator 2) enzymes catalyze a unique protein deacetylation reaction that requires the coenzyme NAD(+) and produces nicotinamide and a newly discovered metabolite, O-acetyl-ADP-ribose (OAADPr). Conserved from bacteria to humans, these proteins are implicated in the control of gene silencing, metabolism, apoptosis, and aging. Here we examine the role of NAD(+) metabolites/derivatives and salvage pathway intermediates as activators, inhibitors, or coenzyme substrates of Sir2 enzymes in vitro. Also, we probe the coenzyme binding site using inhibitor binding studies and alternative coenzyme derivatives as substrates. Sir2 enzymes showed an exquisite selectivity for the nicotinamide base coenzyme, with the most dramatic losses in binding affinity/reactivity resulting from relatively minor changes in the nicotinamide ring, either by reduction, as in NADH, or by converting the amide to its acid analogue. Both ends of the dinucleotide NAD(+) are shown to be critical for high selectivity and high affinity. Among the NAD(+) metabolites tested none were able to allosterically activate, although all led to various extents of inhibition, consistent with competition at the coenzyme binding site. Nicotinamide was the most potent inhibitor examined, suggesting that cellular nicotinamide levels would provide an effective small molecule regulator of protein deacetylation and generation of OAADPr. The presented findings also suggest that changes in the physiological NAD(+):NADH ratio, without a change in NAD(+), would yield little alteration in Sir2 activity. That is, NADH is an extremely ineffective inhibitor of Sir2 enzymes (average IC(50) of 17 mm). We propose that changes in both free nicotinamide and free NAD(+) afford the greatest contribution to cellular activity of Sir2 enzymes but with nicotinamide having a more dramatic effect during smaller fluctuations in concentration.
Author List
Schmidt MT, Smith BC, Jackson MD, Denu JMAuthor
Brian C. Smith PhD Associate Professor in the Biochemistry department at Medical College of WisconsinMESH terms used to index this publication - Major topics in bold
Binding SitesCoenzymes
NAD
Protein Structure, Tertiary
Sirtuins
Substrate Specificity
Yeasts