title: Crystal structures of the bifunctional tRNA methyltransferase Trm5a.
abstract: tRNA methyltransferase Trm5 catalyses the transfer of a methyl group from S-adenosyl-L-methionine to G37 in eukaryotes and archaea. The N1-methylated guanosine is the product of the initial step of the wyosine hypermodification, which is essential for the maintenance of the reading frame during translation. As a unique member of this enzyme family, Trm5a from Pyrococcus abyssi (PaTrm5a) catalyses not only the methylation of N1, but also the further methylation of C7 on 4-demethylwyosine at position 37 to produce isowyosine, but the mechanism for the double methylation is poorly understood. Here we report four crystal structures of PaTrm5a ranging from 1.7- to 2.3-Å, in the apo form or in complex with various SAM analogues. These structures reveal that Asp243 specifically recognises the base moiety of SAM at the active site. Interestingly, the protein in our structures all displays an extended conformation, quite different from the well-folded conformation of Trm5b from Methanocaldococcus jannaschii reported previously, despite their similar overall architectures. To rule out the possibilities of crystallisation artefacts, we conducted the fluorescence resonance energy transfer (FRET) experiments. The FRET data suggested that PaTrm5a adopts a naturally extended conformation in solution, and therefore the open conformation is a genuine state of PaTrm5a.
authors.affiliation: State Key Laboratory for Biocontrol, School of Life Sciences, The Sun Yat-Sen University, Guangzhou, Guangdong 510275, People's Republic of China.|Center for Cellular &Structural biology, The Sun Yat-Sen University, 132 E. Circle Rd., University City, Guangzhou, Guangdong 510006, People's Republic of China.
authors.forename: Caiyan
authors.initials: C
authors.lastname: Wang
authors.affiliation: State Key Laboratory for Biocontrol, School of Life Sciences, The Sun Yat-Sen University, Guangzhou, Guangdong 510275, People's Republic of China.|Center for Cellular &Structural biology, The Sun Yat-Sen University, 132 E. Circle Rd., University City, Guangzhou, Guangdong 510006, People's Republic of China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Jia
authors.affiliation: State Key Laboratory for Biocontrol, School of Life Sciences, The Sun Yat-Sen University, Guangzhou, Guangdong 510275, People's Republic of China.|Center for Cellular &Structural biology, The Sun Yat-Sen University, 132 E. Circle Rd., University City, Guangzhou, Guangdong 510006, People's Republic of China.
authors.forename: Ran
authors.initials: R
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Optoelectronic Materials &Technologies, School of Physics, Sun Yat-Sen University, Guangzhou, Guangdong 510006, China.
authors.forename: Yuming
authors.initials: Y
authors.lastname: Wei
authors.affiliation: State Key Laboratory of Optoelectronic Materials &Technologies, School of Physics, Sun Yat-Sen University, Guangzhou, Guangdong 510006, China.
authors.forename: Juntao
authors.initials: J
authors.lastname: Li
authors.affiliation: State Key Laboratory of Optoelectronic Materials &Technologies, School of Physics, Sun Yat-Sen University, Guangzhou, Guangdong 510006, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Ma
authors.affiliation: State Key Laboratory for Biocontrol, School of Life Sciences, The Sun Yat-Sen University, Guangzhou, Guangdong 510275, People's Republic of China.|Center for Cellular &Structural biology, The Sun Yat-Sen University, 132 E. Circle Rd., University City, Guangzhou, Guangdong 510006, People's Republic of China.
authors.forename: Wei
authors.initials: W
authors.lastname: Xie
mesh_terms: D000595:Amino Acid Sequence; D001059:Apoproteins / Q000737:chemistry; D053898:Biosynthetic Pathways; D018360:Crystallography, X-Ray; D031541:Fluorescence Resonance Energy Transfer; D008958:Models, Molecular; D019711:Pyrococcus / Q000201:enzymology*; D016415:Sequence Alignment; D040681:Structural Homology, Protein; D013379:Substrate Specificity; D012359:tRNA Methyltransferases / Q000737:chemistry* / Q000378:metabolism
chemical_list: D001059:Apoproteins; D012359:tRNA Methyltransferases