title: Variant of human enzyme sequesters reactive intermediate.
abstract: In cellular environments, coupled hydrolytic reactions are used to force efficient product formation in enzyme-catalyzed reactions. In the first step of protein synthesis, aminoacyl-tRNA synthetases react with amino acid and ATP to form an enzyme-bound adenylate that, in the next step, reacts with tRNA to form aminoacyl-tRNA. The reaction liberates pyrophosphate (PP(i)) which, in turn, can be hydrolyzed by pyrophosphatase to drive efficient aminoacylation. A potential polymorphic variant of human tryptophanyl-tRNA synthetase is shown here to sequester tryptophanyl adenylate. The bound adenylate does not react efficiently with the liberated PP(i) that normally competes with tRNA to resynthesize ATP and free amino acid. Structural analysis of this variant showed that residues needed for binding ATP phosphates and thus PP(i) were reoriented from their conformations in the structure of the more common sequence variant. Significantly, the reorientation does not affect reaction with tRNA, so that efficient aminoacylation is achieved.
authors.affiliation: Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, Mail Drop BCC-379, La Jolla, California 92037, USA. kewalt@scripps.edu
authors.forename: Karla L
authors.initials: KL
authors.lastname: Ewalt
authors.forename: Xiang-Lei
authors.initials: XL
authors.lastname: Yang
authors.forename: Francella J
authors.initials: FJ
authors.lastname: Otero
authors.forename: Jianming
authors.initials: J
authors.lastname: Liu
authors.forename: Bonnie
authors.initials: B
authors.lastname: Slike
authors.forename: Paul
authors.initials: P
authors.lastname: Schimmel
mesh_terms: D000249:Adenosine Monophosphate / Q000737:chemistry / Q000378:metabolism; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D002384:Catalysis; D011756:Diphosphates / Q000737:chemistry / Q000378:metabolism; D004789:Enzyme Activation / Q000235:genetics; D014644:Genetic Variation; D006801:Humans; D007700:Kinetics; D008956:Models, Chemical; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D011110:Polymorphism, Genetic; D014364:Tryptophan / Q000737:chemistry / Q000378:metabolism; D014369:Tryptophan-tRNA Ligase / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D011756:Diphosphates; D000249:Adenosine Monophosphate; D014364:Tryptophan; D014369:Tryptophan-tRNA Ligase