Insights into the sirtuin mechanism from ternary complexes containing NAD+ and acetylated peptide. Author Kevin Hoff, José Avalos, Kristin Sens, Cynthia Wolberger Publication Year 2006 Type Journal Article Abstract Sirtuin proteins comprise a unique class of NAD+-dependent protein deacetylases. Although several structures of sirtuins have been determined, the mechanism by which NAD+ cleavage occurs has remained unclear. We report the structures of ternary complexes containing NAD+ and acetylated peptide bound to the bacterial sirtuin Sir2Tm and to a catalytic mutant (Sir2Tm(H116Y)). NAD+ in these structures binds in a conformation different from that seen in previous structures, exposing the alpha face of the nicotinamide ribose to the carbonyl oxygen of the acetyl lysine substrate. The NAD+ conformation is identical in both structures, suggesting that proper coenzyme orientation is not dependent on contacts with the catalytic histidine. We also present the structure of Sir2Tm(H116A) bound to deacteylated peptide and 3'-O-acetyl ADP ribose. Taken together, these structures suggest a mechanism for nicotinamide cleavage in which an invariant phenylalanine plays a central role in promoting formation of the O-alkylamidate reaction intermediate and preventing nicotinamide exchange. Keywords Models, Molecular, Crystallography, X-Ray, Multiprotein Complexes, Peptides, Crystallization, NAD, O-Acetyl-ADP-Ribose, Sirtuins Journal Structure Volume 14 Issue 8 Pages 1231-40 Date Published 2006 Aug ISSN Number 0969-2126 DOI 10.1016/j.str.2006.06.006 Alternate Journal Structure PMID 16905097 PubMedGoogle ScholarBibTeXEndNote X3 XML