title: Conformational movements and cooperativity upon amino acid, ATP and tRNA binding in threonyl-tRNA synthetase.
abstract: The crystal structures of threonyl-tRNA synthetase (ThrRS) from Staphylococcus aureus, with ATP and an analogue of threonyl adenylate, are described. Together with the previously determined structures of Escherichia coli ThrRS with different substrates, they allow a comprehensive analysis of the effect of binding of all the substrates: threonine, ATP and tRNA. The tRNA, by inserting its acceptor arm between the N-terminal domain and the catalytic domain, causes a large rotation of the former. Within the catalytic domain, four regions surrounding the active site display significant conformational changes upon binding of the different substrates. The binding of threonine induces the movement of as much as 50 consecutive amino acid residues. The binding of ATP triggers a displacement, as large as 8A at some C(alpha) positions, of a strand-loop-strand region of the core beta-sheet. Two other regions move in a cooperative way upon binding of threonine or ATP: the motif 2 loop, which plays an essential role in the first step of the aminoacylation reaction, and the ordering loop, which closes on the active site cavity when the substrates are in place. The tRNA interacts with all four mobile regions, several residues initially bound to threonine or ATP switching to a position in which they can contact the tRNA. Three such conformational switches could be identified, each of them in a different mobile region. The structural analysis suggests that, while the small substrates can bind in any order, they must be in place before productive tRNA binding can occur.
authors.affiliation: Laboratoire de Biologie et Génomique Structurales, IGBMC, 1 rue Laurent Fries, BP 10142, 67400 Illkirch Cedex, France.
authors.forename: Alfredo
authors.initials: A
authors.lastname: Torres-Larios
authors.forename: Rajan
authors.initials: R
authors.lastname: Sankaranarayanan
authors.forename: Bernard
authors.initials: B
authors.lastname: Rees
authors.forename: Anne Catherine
authors.initials: AC
authors.lastname: Dock-Bregeon
authors.forename: Dino
authors.initials: D
authors.lastname: Moras
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry* / Q000378:metabolism; D000596:Amino Acids / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry; D001665:Binding Sites; D020134:Catalytic Domain; D003460:Crystallization; D004926:Escherichia coli / Q000201:enzymology; D015394:Molecular Structure; D009038:Motion; D011485:Protein Binding; D011487:Protein Conformation; D012343:RNA, Transfer / Q000737:chemistry* / Q000378:metabolism; D013211:Staphylococcus aureus / Q000201:enzymology; D013912:Threonine / Q000737:chemistry* / Q000378:metabolism; D013914:Threonine-tRNA Ligase / Q000737:chemistry* / Q000378:metabolism
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D013912:Threonine; D000255:Adenosine Triphosphate; D012343:RNA, Transfer; D013914:Threonine-tRNA Ligase