title: Structure and substrate binding properties of cobB, a Sir2 homolog protein deacetylase from Escherichia coli.
abstract: Sirtuins are NAD+-dependent protein deacetylase enzymes that are broadly conserved from bacteria to human, and have been implicated to play important roles in gene regulation, metabolism and longevity. cobB is a bacterial sirtuin that deacetylates acetyl-CoA synthetase (Acs) at an active site lysine to stimulate its enzymatic activity. Here, we report the structure of cobB bound to an acetyl-lysine containing non-cognate histone H4 substrate. A comparison with the previously reported archaeal and eukaryotic sirtuin structures reveals the greatest variability in a small zinc-binding domain implicated to play a particularly important role in substrate-specific binding by the sirtuin proteins. Comparison of the cobB/histone H4 complex with other sirtuin proteins in complex with acetyl-lysine containing substrates, further suggests that contacts to the acetyl-lysine side-chain and beta-sheet interactions with residues directly C-terminal to the acetyl-lysine represent conserved features of sirtuin-substrate recognition. Isothermal titration calorimetry studies were used to compare the affinity of cobB for a variety of cognate and non-cognate acetyl-lysine-bearing peptides revealing an exothermic reaction with relatively little discrimination between substrates. In contrast, similar studies employing intact acetylated Acs protein as a substrate reveal a binding reaction that is endothermic, suggesting that cobB recognition of substrate involves a burial of hydrophobic surface and/or structural rearrangement involving substrate regions distal to the acetyl-lysine-binding site. Together, these studies suggest that substrate-specific binding by sirtuin proteins involves contributions from the zinc-binding domain of the enzyme and substrate regions distal to the acetyl-lysine-binding site.
authors.affiliation: The Wistar Institute, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Kehao
authors.initials: K
authors.lastname: Zhao
authors.forename: Xiaomei
authors.initials: X
authors.lastname: Chai
authors.forename: Ronen
authors.initials: R
authors.lastname: Marmorstein
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D029968:Escherichia coli Proteins / Q000737:chemistry*; D006657:Histones; D008239:Lysine / Q000737:chemistry; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D037761:Sirtuins / Q000737:chemistry*; D040681:Structural Homology, Protein; D013379:Substrate Specificity
chemical_list: D029968:Escherichia coli Proteins; D006657:Histones; D037761:Sirtuins; D008239:Lysine