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Search The CSA
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Catalytic Site Atlas

CSA LITERATURE entry for 1pud

E.C. nametRNA-guanine transglycosylase
SpeciesZymomonas mobilis ()
E.C. Number (IntEnz) 2.4.2.29
CSA Homologues of 1pudThere are 58 Homologs
CSA Entries With UniProtID P28720
CSA Entries With EC Number 2.4.2.29
PDBe Entry 1pud
PDBSum Entry 1pud
MACiE Entry 1pud

Literature Report

IntroductionA variety of modified bases are found in RNAs and around 1% of the Escherichia coli genome codes for proteins involved in tRNA modification. The hypermodified base quenine, a 7-deazaguanine derivative, replaces guanine-34 at the wobble position of tRNAs specific for Asn, Asp, His and Tyr. In vitro and in vivo studies showed that quenine in tRNAs affects codon selection and prevents stop codon readthrough of tobacco mosaic virus RNA in a codon context-dependent manner. However, its general function remains not very well understood [1]. Quenine is synthesised de novo in prokaryotes, whereas it is a nutrient for eukaryotes. In prokaryotes, the quenine biosynthesis requires several steps, not all of them yet known [1]. The biosynthesis begins outside of the tRNA with the conversion of GTP to the quenine precursor 7-aminomethyl-7-deazaguanine (preQ1). tRNA-guanine transglycosylase (TGT) replaces the guanine-34 at the wobble position of the cognate tRNAs with preQ1. tRNA-preQ1 is modified further by the S-adenosylmethionine-requiring enzyme QueA and an unknown vitamin B12-dependent enzyme leading to quenine [1].
MechansimThe catalytic mechanism proposed on the basis of the crystal structure determination of TGT [2]. (1) The carboxylate group of Asp 102 first attacks the wobble guanosine at the C1' atom, leading to guanine release and formation of a covalent bond between the aspartate sidechain and the ribose in an alpha-configuration. (2) The second reaction catalysed by TGT is the substitution of the aspartate 102 by preQ1, leading to the formation of the final preQ1-modified tRNA. It has been proposed that deprotonation of preQ1 nitrogen N9 occurs before it attacks the C1' atom.
Reaction

Catalytic Sites for 1pud

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
AspA102102macie:sideChain

Literature References

Notes:
Romier C.
Crystal structure of tRNA-guanine transglycosylase: RNA modification by base exchange
EMBL J 1996 15 2850-2857
PubMed: 8654383
Romier C.
Mutagenesis and crystallographic studies of Zymomonas mobilis tRNA-guanine transglycosylase reveal aspartate 102 as the active site nucleophile
Biochemistry 1996 35 15734-157339
PubMed: 8961936
Gradler U.
Mutagenesis and crystallographic studies of Zymomonas mobilis tRNA-guanine transglycosylase to elucidate the role of serine 103 for enzymatic activity
FEBS Lett 1999 35 15734-157339
PubMed: 10413112
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