title: Crystal structure of tRNA-guanine transglycosylase: RNA modification by base exchange.
abstract: tRNA-guanine transglycosylases (TGT) are enzymes involved in the modification of the anticodon of tRNAs specific for Asn, Asp, His and Tyr, leading to the replacement of guanine-34 at the wobble position by the hypermodified base queuine. In prokaryotes TGT catalyzes the exchange of guanine-34 with the queuine (.)precursor 7-aminomethyl-7-deazaguanine (preQ1). The crystal structure of TGT from Zymomonas mobilis was solved by multiple isomorphous replacement and refined to a crystallographic R-factor of 19% at 1.85 angstrom resolution. The structure consists of an irregular (beta/alpha)8-barrel with a tightly attached C-terminal zinc-containing subdomain. The packing of the subdomain against the barrel is mediated by an alpha-helix, located close to the C-terminus, which displaces the eighth helix of the barrel. The structure of TGT in complex with preQ1 suggests a binding mode for tRNA where the phosphate backbone interacts with the zinc subdomain and the U33G34U35 sequence is recognized by the barrel. This model for tRNA binding is consistent with a base exchange mechanism involving a covalent tRNA-enzyme intermediate. This structure is the first example of a (beta/alpha)-barrel protein interacting specifically with a nucleic acid.
authors.affiliation: European Molecular Biology Laboratory, Structural Biology Programme, Heidelberg, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Romier
authors.forename: K
authors.initials: K
authors.lastname: Reuter
authors.forename: D
authors.initials: D
authors.lastname: Suck
authors.forename: R
authors.initials: R
authors.lastname: Ficner
mesh_terms: D000595:Amino Acid Sequence; D000926:Anticodon / Q000378:metabolism; D002384:Catalysis; D018360:Crystallography, X-Ray; D006147:Guanine / Q000031:analogs & derivatives / Q000378:metabolism; D008667:Metalloproteins / Q000648:ultrastructure; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009694:Nucleic Acid Precursors / Q000378:metabolism; D010430:Pentosyltransferases / Q000648:ultrastructure*; D011744:Pyrimidinones / Q000378:metabolism; D011758:Pyrroles / Q000378:metabolism; D012343:RNA, Transfer / Q000378:metabolism*; D011994:Recombinant Proteins; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D015032:Zinc / Q000737:chemistry; D017355:Zymomonas / Q000201:enzymology*
chemical_list: C096876:7-(aminomethyl)-7-deazaguanine; D000926:Anticodon; D008667:Metalloproteins; D009694:Nucleic Acid Precursors; D011744:Pyrimidinones; D011758:Pyrroles; D011994:Recombinant Proteins; D006147:Guanine; C019549:queuine; D012343:RNA, Transfer; D010430:Pentosyltransferases; C020837:queuine tRNA-ribosyltransferase; D015032:Zinc