title: Use of substrate analogs and mutagenesis to study substrate binding and catalysis in the Sir2 family of NAD-dependent protein deacetylases.
abstract: The Sir2 family of enzymes is highly conserved throughout evolution and functions in silencing, control of life span, apoptosis, and many other cellular processes. Since the discovery of the NAD-dependent deacetylase activity of Sir2 proteins, there has been a flurry of activity aiming to uncover the mode of substrate binding and catalysis. Structural and biochemical studies have led to several proposed reaction mechanisms, yet the exact catalytic steps remain unclear. Here we present in vitro studies of yeast homolog Hst2 that shed light on the mechanism of Sir2 proteins. Using acetyl-lysine substrate analogs, we demonstrate that the Hst2 reaction proceeds via an initial SN2-type mechanism with the direct formation of an ADP-ribose-acetyl-lysine intermediate. Kinetic studies further suggest that ADP-ribose inhibits the Hst2 reaction in a biologically relevant manner. Through biochemical and kinetic analyses of point mutants, we also clarify the role of several conserved core domain residues in substrate binding, stabilization of the ADP-ribose-acetyl-lysine intermediate, and catalysis. These findings bring us a few steps closer to understanding Sir2 activity and may provide a useful platform for the design of Sir2-specific inhibitors for analysis of Sir2 function and possibly therapeutic applications.
authors.affiliation: Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
authors.forename: Ahlia N
authors.initials: AN
authors.lastname: Khan
authors.forename: Peter N
authors.initials: PN
authors.lastname: Lewis
mesh_terms: D000107:Acetylation; D000595:Amino Acid Sequence; D001665:Binding Sites; D002384:Catalysis; D006655:Histone Deacetylases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008239:Lysine / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009243:NAD / Q000378:metabolism*; D038961:O-Acetyl-ADP-Ribose / Q000737:chemistry / Q000378:metabolism*; D017354:Point Mutation; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D056565:Sirtuin 2; D037761:Sirtuins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D038961:O-Acetyl-ADP-Ribose; D029701:Saccharomyces cerevisiae Proteins; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D009243:NAD; C423033:HST2 protein, S cerevisiae; C087778:SIR2 protein, S cerevisiae; D056565:Sirtuin 2; D037761:Sirtuins; D006655:Histone Deacetylases; D008239:Lysine