title: Crystal structure of archaeosine tRNA-guanine transglycosylase.
abstract: Archaeosine tRNA-guanine transglycosylase (ArcTGT) catalyzes the exchange of guanine at position 15 in the D-loop of archaeal tRNAs with a free 7-cyano-7-deazaguanine (preQ(0)) base, as the first step in the biosynthesis of an archaea-specific modified base, archaeosine (7-formamidino-7-deazaguanosine). We determined the crystal structures of ArcTGT from Pyrococcus horikoshii at 2.2 A resolution and its complexes with guanine and preQ(0), at 2.3 and 2.5 A resolutions, respectively. The N-terminal catalytic domain folds into an (alpha/beta)(8) barrel with a characteristic zinc-binding site, showing structural similarity with that of the bacterial queuosine TGT (QueTGT), which is involved in queuosine (7-[[(4,5-cis-dihydroxy-2-cyclopenten-1-yl)-amino]methyl]-7-deazaguanosine) biosynthesis and targets the tRNA anticodon. ArcTGT forms a dimer, involving the zinc-binding site and the ArcTGT-specific C-terminal domain. The C-terminal domains have novel folds, including an OB fold-like "PUA domain", whose sequence is widely conserved in eukaryotic and archaeal RNA modification enzymes. Therefore, the C-terminal domains may be involved in tRNA recognition. In the free-form structure of ArcTGT, an alpha-helix located at the rim of the (alpha/beta)(8) barrel structure is completely disordered, while it is ordered in the guanine-bound and preQ(0)-bound forms. Structural comparison of the ArcTGT.preQ(0), ArcTGT.guanine, and QueTGT.preQ(1) complexes provides novel insights into the substrate recognition mechanisms of ArcTGT.
authors.affiliation: Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Ryuichiro
authors.initials: R
authors.lastname: Ishitani
authors.forename: Osamu
authors.initials: O
authors.lastname: Nureki
authors.forename: Shuya
authors.initials: S
authors.lastname: Fukai
authors.forename: Teiya
authors.initials: T
authors.lastname: Kijimoto
authors.forename: Nobukazu
authors.initials: N
authors.lastname: Nameki
authors.forename: Masakatsu
authors.initials: M
authors.lastname: Watanabe
authors.forename: Hisao
authors.initials: H
authors.lastname: Kondo
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Sekine
authors.forename: Norihiro
authors.initials: N
authors.lastname: Okada
authors.forename: Susumu
authors.initials: S
authors.lastname: Nishimura
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Yokoyama
mesh_terms: D000595:Amino Acid Sequence; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D019281:Dimerization; D006147:Guanine / Q000031:analogs & derivatives* / Q000096:biosynthesis; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009704:Nucleoside Q / Q000096:biosynthesis; D010430:Pentosyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011487:Protein Conformation; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D019711:Pyrococcus / Q000201:enzymology / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity
chemical_list: D009704:Nucleoside Q; D006147:Guanine; D010430:Pentosyltransferases; C020837:queuine tRNA-ribosyltransferase; C066856:7-deazaguanine