title: Crystal structure of archaeal tRNA(m(1)G37)methyltransferase aTrm5.
abstract: Methylation of the N1 atom of guanosine at position 37 in tRNA, the position 3'-adjacent to the anticodon, generates the modified nucleoside m(1)G37. In archaea and eukaryotes, m(1)G37 synthesis is catalyzed by tRNA(m(1)G37)methyltransferase (archaeal or eukaryotic Trm5, a/eTrm5). Here we report the crystal structure of archaeal Trm5 (aTrm5) from Methanocaldococcus jannaschii (formerly known as Methanococcus jannaschii) in complex with the methyl donor analogue at 2.2 A resolution. The crystal structure revealed that the entire protein is composed of three structural domains, D1, D2, and D3. In the a/eTrm5 primary structures, D2 and D3 are highly conserved, while D1 is not conserved. The D3 structure is the Rossmann fold, which is the hallmark of the canonical class-I methyltransferases. The a/eTrm5-defining domain, D2, exhibits structural similarity to some class-I methyltransferases. In contrast, a DALI search with the D1 structure yielded no structural homologues. In the crystal structure, D3 contacts both D1 and D2. The residues involved in the D1:D3 interactions are not conserved, while those participating in the D2:D3 interactions are well conserved. D1 and D2 do not contact each other, and the linker between them is disordered. aTrm5 fragments corresponding to the D1 and D2-D3 regions were prepared in a soluble form. The NMR analysis of the D1 fragment revealed that D1 is well folded by itself, and it did not interact with either the D2-D3 fragment or the tRNA. The NMR analysis of the D2-D3 fragment revealed that it is well folded, independently of D1, and that it interacts with tRNA. Furthermore, the D2-D3 fragment was as active as the full-length enzyme for tRNA methylation. The positive charges on the surface of D2-D3 may be involved in tRNA binding. Therefore, these findings suggest that the interaction between D1 and D3 is not persistent, and that the D2-D3 region plays the major role in tRNA methylation.
authors.affiliation: Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Sakurako
authors.initials: S
authors.lastname: Goto-Ito
authors.forename: Takuhiro
authors.initials: T
authors.lastname: Ito
authors.forename: Ryohei
authors.initials: R
authors.lastname: Ishii
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Muto
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Bessho
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Yokoyama
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019843:Archaeal Proteins / Q000737:chemistry*; D020134:Catalytic Domain; D003001:Cloning, Molecular; D003460:Crystallization; D018360:Crystallography, X-Ray; D006801:Humans; D017017:Methanococcus / Q000201:enzymology*; D008745:Methylation; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D012359:tRNA Methyltransferases / Q000737:chemistry*
chemical_list: D019843:Archaeal Proteins; D012359:tRNA Methyltransferases; C036950:tRNA (guanine-N1-)-methyltransferase; C489294:TRMT5 protein, human