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Crystal structure of tRNA‐guanine transglycosylase: RNA modification by base exchange.
Author(s) -
Romier C.,
Reuter K.,
Suck D.,
Ficner R.
Publication year - 1996
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1002/j.1460-2075.1996.tb00646.x
Subject(s) - guanine , wobble base pair , transfer rna , biology , stereochemistry , rna , nucleic acid , base pair , biochemistry , protein structure , crystallography , nucleotide , dna , chemistry , gene
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.