title: The archaeal transamidosome for RNA-dependent glutamine biosynthesis.
abstract: Archaea make glutaminyl-tRNA (Gln-tRNA(Gln)) in a two-step process; a non-discriminating glutamyl-tRNA synthetase (ND-GluRS) forms Glu-tRNA(Gln), while the heterodimeric amidotransferase GatDE converts this mischarged tRNA to Gln-tRNA(Gln). Many prokaryotes synthesize asparaginyl-tRNA (Asn-tRNA(Asn)) in a similar manner using a non-discriminating aspartyl-tRNA synthetase (ND-AspRS) and the heterotrimeric amidotransferase GatCAB. The transamidosome, a complex of tRNA synthetase, amidotransferase and tRNA, was first described for the latter system in Thermus thermophilus [Bailly, M., Blaise, M., Lorber, B., Becker, H.D. and Kern, D. (2007) The transamidosome: a dynamic ribonucleoprotein particle dedicated to prokaryotic tRNA-dependent asparagine biosynthesis. Mol. Cell, 28, 228-239.]. Here, we show a similar complex for Gln-tRNA(Gln) formation in Methanothermobacter thermautotrophicus that allows the mischarged Glu-tRNA(Gln) made by the tRNA synthetase to be channeled to the amidotransferase. The association of archaeal ND-GluRS with GatDE (K(D) = 100 ± 22 nM) sequesters the tRNA synthetase for Gln-tRNA(Gln) formation, with GatDE reducing the affinity of ND-GluRS for tRNA(Glu) by at least 13-fold. Unlike the T. thermophilus transamidosome, the archaeal complex does not require tRNA for its formation, is not stable through product (Gln-tRNA(Gln)) formation, and has no major effect on the kinetics of tRNA(Gln) glutamylation nor transamidation. The differences between the two transamidosomes may be a consequence of the fact that ND-GluRS is a class I aminoacyl-tRNA synthetase, while ND-AspRS belongs to the class II family.
authors.affiliation: Department of Molecular Biophysics and Biochemistry and Department of Chemistry, Yale University, New Haven, CT 06511, USA.
authors.forename: Theodoros
authors.initials: T
authors.lastname: Rampias
authors.forename: Kelly
authors.initials: K
authors.lastname: Sheppard
authors.forename: Dieter
authors.initials: D
authors.lastname: Söll
mesh_terms: D005975:Glutamate-tRNA Ligase / Q000378:metabolism*; D005973:Glutamine / Q000096:biosynthesis*; D017013:Methanobacteriaceae / Q000201:enzymology*; D019884:Nitrogenous Group Transferases / Q000378:metabolism*; D012351:RNA, Transfer, Gln / Q000378:metabolism*; D012352:RNA, Transfer, Glu / Q000378:metabolism; D046249:Transfer RNA Aminoacylation
chemical_list: D012351:RNA, Transfer, Gln; D012352:RNA, Transfer, Glu; D005973:Glutamine; D019884:Nitrogenous Group Transferases; C047694:glutamyl-tRNA(Gln) amidotransferase; D005975:Glutamate-tRNA Ligase
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