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.
Highlights
Diverse modifications in tRNAs serve various purposes including promoting translational fidelity[1,2,3]
Crécy-Lagard et al recently discovered that the Trm[5] enzyme from the archaea Pyrococcus abyssi (PaTrm5a) catalyzes the methylation of C7 on imG-14 to produce imG211, which is further methylated on the N4 position of the imidazo-purine ring by Taw[3] to form mimG
Trm5cs at their N-termini are absent from some Trm5as11. aTrm5s have the Rossmann fold at the C-termini for catalysis, with the consensus NPPY motif located in the fourth β-strand of the Rossmann fold
Summary
Diverse modifications in tRNAs serve various purposes including promoting translational fidelity[1,2,3]. Crécy-Lagard et al recently discovered that the Trm[5] enzyme from the archaea Pyrococcus abyssi (PaTrm5a) catalyzes the methylation of C7 on imG-14 to produce imG211, which is further methylated on the N4 position of the imidazo-purine ring by Taw[3] to form mimG. The crystal structures of MjTrm5b complexed with the substrates tRNALeu and tRNACys were solved (PDBs 2ZZM and 2ZZN respectively). In both structures, D1 acts like a clamp and contacts the elbow region of tRNA, while D2 recognises G37 and the anticodon loop. Trm5a from Pyrococcus abyssi (PaTrm5a) is a newly discovered methyltransferase that catalyses two distinct reactions in tRNA: the N1-methylation of G and the C7-methylation of imG-14 at position 3711 (Fig. 1). The naturally extended conformation exhibited by PaTrm5a was confirmed by the fluorescence resonance energy transfer (FRET) experimental data
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
