title: Role of motif III in catalysis by acetyl-CoA synthetase.
abstract: The acyl-adenylate-forming enzyme superfamily, consisting of acyl- and aryl-CoA synthetases, the adenylation domain of the nonribosomal peptide synthetases, and luciferase, has three signature motifs (I-III) and ten conserved core motifs (A1-A10), some of which overlap the signature motifs. The consensus sequence for signature motif III (core motif A7) in acetyl-CoA synthetase is Y-X-S/T/A-G-D, with an invariant fifth position, highly conserved first and fourth positions, and variable second and third positions. Kinetic studies of enzyme variants revealed that an alteration at any position resulted in a strong decrease in the catalytic rate, although the most deleterious effects were observed when the first or fifth positions were changed. Structural modeling suggests that the highly conserved Tyr in the first position plays a key role in active site architecture through interaction with a highly conserved active-site Gln, and the invariant Asp in the fifth position plays a critical role in ATP binding and catalysis through interaction with the 2'- and 3'-OH groups of the ribose moiety. Interactions between these Asp and ATP are observed in all structures available for members of the superfamily, consistent with a critical role in substrate binding and catalysis for this invariant residue.
authors.affiliation: Department of Genetics and Biochemistry, Clemson University, Clemson, SC 29634-0318, USA.
authors.forename: Cheryl
authors.initials: C
authors.lastname: Ingram-Smith
authors.forename: Jerry L
authors.initials: JL
authors.lastname: Thurman
authors.forename: Karen
authors.initials: K
authors.lastname: Zimowski
authors.forename: Kerry S
authors.initials: KS
authors.lastname: Smith
mesh_terms: D000106:Acetate-CoA Ligase / Q000235:genetics / Q000378:metabolism*; D000241:Adenosine / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000235:genetics / Q000378:metabolism*; D020134:Catalytic Domain; D017124:Conserved Sequence; D004789:Enzyme Activation; D057075:Enzyme Assays; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D017013:Methanobacteriaceae / Q000201:enzymology* / Q000235:genetics; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D011487:Protein Conformation; D025941:Protein Interaction Mapping; D012266:Ribose / Q000378:metabolism; D016415:Sequence Alignment; D014443:Tyrosine / Q000378:metabolism
chemical_list: D019843:Archaeal Proteins; D014443:Tyrosine; D012266:Ribose; D000255:Adenosine Triphosphate; D000106:Acetate-CoA Ligase; D000241:Adenosine