title: Crystal structure of Thermus thermophilus tRNA m1A58 methyltransferase and biophysical characterization of its interaction with tRNA.
abstract: Methyltransferases from the m(1)A(58) tRNA methyltransferase (TrmI) family catalyze the S-adenosyl-l-methionine-dependent N(1)-methylation of tRNA adenosine 58. The crystal structure of Thermus thermophilus TrmI, in complex with S-adenosyl-l-homocysteine, was determined at 1.7 A resolution. This structure is closely related to that of Mycobacterium tuberculosis TrmI, and their comparison enabled us to enlighten two grooves in the TrmI structure that are large enough and electrostatically compatible to accommodate one tRNA per face of TrmI tetramer. We have then conducted a biophysical study based on electrospray ionization mass spectrometry, site-directed mutagenesis, and molecular docking. First, we confirmed the tetrameric oligomerization state of TrmI, and we showed that this protein remains tetrameric upon tRNA binding, with formation of complexes involving one to two molecules of tRNA per TrmI tetramer. Second, three key residues for the methylation reaction were identified: the universally conserved D170 and two conserved aromatic residues Y78 and Y194. We then used molecular docking to position a N(9)-methyladenine in the active site of TrmI. The N(9)-methyladenine snugly fits into the catalytic cleft, where the side chain of D170 acts as a bidentate ligand binding the amino moiety of S-adenosyl-l-methionine and the exocyclic amino group of the adenosine. Y194 interacts with the N(9)-methyladenine ring, whereas Y78 can stabilize the sugar ring. From our results, we propose that the conserved residues that form the catalytic cavity (D170, Y78, and Y194) are essential for fashioning an optimized shape of the catalytic pocket.
authors.affiliation: Laboratoire de Cristallographie et RMN biologiques, Université Paris-Descartes, CNRS UMR 8015, 4 avenue de l'Observatoire, 75006 Paris, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Barraud
authors.forename: Béatrice
authors.initials: B
authors.lastname: Golinelli-Pimpaneau
authors.forename: Cédric
authors.initials: C
authors.lastname: Atmanene
authors.forename: Sarah
authors.initials: S
authors.lastname: Sanglier
authors.forename: Alain
authors.initials: A
authors.lastname: Van Dorsselaer
authors.forename: Louis
authors.initials: L
authors.lastname: Droogmans
authors.forename: Frédéric
authors.initials: F
authors.lastname: Dardel
authors.forename: Carine
authors.initials: C
authors.lastname: Tisné
mesh_terms: D000225:Adenine / Q000737:chemistry / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D055592:Biophysical Phenomena; D001703:Biophysics; D002384:Catalysis; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009169:Mycobacterium tuberculosis / Q000201:enzymology; D009994:Osmolar Concentration; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D012343:RNA, Transfer / Q000737:chemistry* / Q000378:metabolism*; D016415:Sequence Alignment; D021241:Spectrometry, Mass, Electrospray Ionization; D055672:Static Electricity; D040681:Structural Homology, Protein; D013379:Substrate Specificity; D016963:Thermus thermophilus / Q000201:enzymology* / Q000235:genetics; D012359:tRNA Methyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D012343:RNA, Transfer; D012359:tRNA Methyltransferases; D000225:Adenine