title: Aminoacylation at the Atomic Level in Class IIa Aminoacyl-tRNA Synthetases.
abstract: Abstract   The crystal structures of histidyl- (HisRS) and threonyl-tRNA synthetase (ThrRS) from E. coli and glycyl-tRNA synthetase (GlyRS) from T. thermophilus, all homodimeric class IIa enzymes, were determined in enzyme-substrate and enzyme-product states corresponding to the two steps of aminoacylation. HisRS was complexed with the histidine analog histidinol plus ATP and with histidyl-adenylate, while GlyRS was complexed with ATP and with glycyl-adenylate; these complexes represent the enzyme-substrate and enzyme-product states of the first step of aminoacylation, i.e. the amino acid activation. In both enzymes the ligands occupy the substrate-binding pocket of the N-terminal active site domain, which contains the classical class II aminoacyl-tRNA synthetase fold. HisRS interacts in the same fashion with the histidine, adenosine and α-phosphate moieties of the substrates and intermediate, and GlyRS interacts in the same way with the adenosine and α-phosphate moieties in both states. In addition to the amino acid recognition, there is one key mechanistic difference between the two enzymes: HisRS uses an arginine whereas GlyRS employs a magnesium ion to catalyze the activation of the amino acid. ThrRS was complexed with its cognate tRNA and ATP, which represents the enzyme-substrate state of the second step of aminoacylation, i.e. the transfer of the amino acid to the 3'-terminal ribose of the tRNA. All three enzymes utilize class II conserved residues to interact with the adenosine-phosphate. ThrRS binds tRNA(Thr) so that the acceptor stem enters the active site pocket above the adenylate, with the 3'-terminal OH positioned to pick up the amino acid, and the anticodon loop interacts with the C-terminal domain whose fold is shared by all three enzymes. We can thus extend the principles of tRNA binding to the other two enzymes.
authors.affiliation: a      Laboratoire de Biologie Structurale   ,  Institut de Génétique et de Biologie Moléculaire et Cellulaire   ,  CNRS/INSERM/ULP, BP 163 ,    67404   ,    Illkirch Cedex   ,    France.
authors.forename: J G
authors.initials: JG
authors.lastname: Arnez
authors.forename: R
authors.initials: R
authors.lastname: Sankaranarayanan
authors.forename: A C
authors.initials: AC
authors.lastname: Dock-Bregeon
authors.forename: C S
authors.initials: CS
authors.lastname: Francklyn
authors.forename: D
authors.initials: D
authors.lastname: Moras
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry; D000604:Amino Acyl-tRNA Synthetases / Q000737:chemistry; D049148:Aminoacylation; D000926:Anticodon; D001665:Binding Sites; D020134:Catalytic Domain; D004926:Escherichia coli / Q000378:metabolism; D008969:Molecular Sequence Data
chemical_list: D000926:Anticodon; D000255:Adenosine Triphosphate; D000604:Amino Acyl-tRNA Synthetases