title: Structural basis for the mechanism and regulation of Sir2 enzymes.
abstract: Sir2 proteins form a family of NAD(+)-dependent protein deacetylases required for diverse biological processes, including transcriptional silencing, suppression of rDNA recombination, control of p53 activity, regulation of acetyl-CoA synthetase, and aging. Although structures of Sir2 enzymes in the presence and absence of peptide substrate or NAD(+) have been determined, the role of the enzyme in the mechanism of deacetylation and NAD(+) cleavage is still unclear. Here, we present additional structures of Sir2Af2 in several differently complexed states: in a productive complex with NAD(+), in a nonproductive NAD(+) complex with bound ADP-ribose, and in the unliganded state. We observe a new mode of NAD(+) binding that seems to depend on acetyl-lysine binding, in which the nicotinamide ring of NAD(+) is buried in the highly conserved "C" pocket of the enzyme. We propose a detailed structure-based mechanism for deacetylation and nicotinamide inhibition of Sir2 consistent with mutagenesis and enzymatic studies.
authors.affiliation: Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205 USA.
authors.forename: José L
authors.initials: JL
authors.lastname: Avalos
authors.forename: Jef D
authors.initials: JD
authors.lastname: Boeke
authors.forename: Cynthia
authors.initials: C
authors.lastname: Wolberger
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000595:Amino Acid Sequence; D001105:Archaea / Q000201:enzymology* / Q000235:genetics; D019843:Archaeal Proteins / Q000737:chemistry* / Q000378:metabolism*; D020134:Catalytic Domain / Q000502:physiology; D008239:Lysine / Q000378:metabolism; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009243:NAD / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D017386:Sequence Homology, Amino Acid; D037761:Sirtuins / Q000737:chemistry* / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D019843:Archaeal Proteins; D046911:Macromolecular Substances; D009243:NAD; D000246:Adenosine Diphosphate Ribose; D037761:Sirtuins; D008239:Lysine