The Enzyme Database

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EC 2.4.2.48     
Accepted name: tRNA-guanine15 transglycosylase
Reaction: guanine15 in tRNA + 7-cyano-7-carbaguanine = 7-cyano-7-carbaguanine15 in tRNA + guanine
Glossary: 7-cyano-7-carbaguanine = preQ0 = 7-cyano-7-deazaguanine
archaeosine = G* = 7-amidino-7-deazaguanosine
Other name(s): tRNA transglycosylase (ambiguous); transfer ribonucleate glycosyltransferase (ambiguous); tRNA guanine15 transglycosidase; TGT (ambiguous); transfer ribonucleic acid guanine15 transglycosylase
Systematic name: tRNA-guanine15:7-cyano-7-carbaguanine tRNA-D-ribosyltransferase
Comments: Archaeal tRNAs contain the modified nucleoside archaeosine at position 15. This archaeal enzyme catalyses the exchange of guanine at position 15 of tRNA with the base preQ0, which is ultimately modified to form the nucleoside archaeosine (cf. EC 2.6.1.97) [1].
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB
References:
1.  Bai, Y., Fox, D.T., Lacy, J.A., Van Lanen, S.G. and Iwata-Reuyl, D. Hypermodification of tRNA in thermophilic archaea. Cloning, overexpression, and characterization of tRNA-guanine transglycosylase from Methanococcus jannaschii. J. Biol. Chem. 275 (2000) 28731–28738. [DOI] [PMID: 10862614]
[EC 2.4.2.48 created 2012]
 
 
EC 2.6.1.97     
Accepted name: archaeosine synthase
Reaction: L-glutamine + 7-cyano-7-carbaguanine15 in tRNA + H2O = L-glutamate + archaeine15 in tRNA
Glossary: 7-cyano-7-carbaguanine = preQ0 = 7-cyano-7-deazaguanine
archaeine = 7-deaza-7-carbamidoylguanine = base G*
archaeosine = G* = 7-amidino-7-deazaguanosine
Other name(s): ArcS; TgtA2; MJ1022 (gene name); glutamine:preQ0-tRNA amidinotransferase (incorrect)
Systematic name: L-glutamine:7-cyano-7-carbaguanine aminotransferase
Comments: In Euryarchaeota the reaction is catalysed by ArcS [1,2]. In Crenarchaeota, which do not have an ArcS homologue, the reaction is catalysed either by a homologue of EC 6.3.4.20, 7-cyano-7-deazaguanine synthase that includes a glutaminase domain (cf. EC 3.5.1.2), or by a homologue of EC 1.7.1.13, preQ1 synthase [2]. The enzyme from the Euryarchaeon Methanocaldococcus jannaschii can also use arginine and ammonium as amino donors.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
References:
1.  Phillips, G., Chikwana, V.M., Maxwell, A., El-Yacoubi, B., Swairjo, M.A., Iwata-Reuyl, D. and de Crecy-Lagard, V. Discovery and characterization of an amidinotransferase involved in the modification of archaeal tRNA. J. Biol. Chem. 285 (2010) 12706–12713. [DOI] [PMID: 20129918]
2.  Phillips, G., Swairjo, M.A., Gaston, K.W., Bailly, M., Limbach, P.A., Iwata-Reuyl, D. and de Crecy-Lagard, V. Diversity of archaeosine synthesis in crenarchaeota. ACS Chem. Biol. 7 (2012) 300–305. [DOI] [PMID: 22032275]
[EC 2.6.1.97 created 2012]
 
 


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