title: The output of the tRNA modification pathways controlled by the Escherichia coli MnmEG and MnmC enzymes depends on the growth conditions and the tRNA species.
abstract: In Escherichia coli, the MnmEG complex modifies transfer RNAs (tRNAs) decoding NNA/NNG codons. MnmEG catalyzes two different modification reactions, which add an aminomethyl (nm) or carboxymethylaminomethyl (cmnm) group to position 5 of the anticodon wobble uridine using ammonium or glycine, respectively. In tRNA(cmnm5s2UUG)(Gln) and tRNA(cmnm5UmAA)(Leu), however, cmnm(5) appears as the final modification, whereas in the remaining tRNAs, the MnmEG products are converted into 5-methylaminomethyl (mnm(5)) through the two-domain, bi-functional enzyme MnmC. MnmC(o) transforms cmnm(5) into nm(5), whereas MnmC(m) converts nm(5) into mnm(5), thus producing an atypical network of modification pathways. We investigate the activities and tRNA specificity of MnmEG and the MnmC domains, the ability of tRNAs to follow the ammonium or glycine pathway and the effect of mnmC mutations on growth. We demonstrate that the two MnmC domains function independently of each other and that tRNA(cmnm5s2UUG)(Gln) and tRNA(cmnm5UmAA)(Leu), are substrates for MnmC(m), but not MnmC(o). Synthesis of mnm(5)s(2)U by MnmEG-MnmC in vivo avoids build-up of intermediates in tRNA(mnm5s2UUU)(Lys). We also show that MnmEG can modify all the tRNAs via the ammonium pathway. Strikingly, the net output of the MnmEG pathways in vivo depends on growth conditions and tRNA species. Loss of any MnmC activity has a biological cost under specific conditions.
authors.affiliation: Laboratory of RNA Modification and Mitochondrial Diseases, Príncipe Felipe Research Center, 46012-Valencia, Spain, Department of Molecular Biology, Umeå University, S90187, Sweden and Biomedical Research Networking Centre for Rare Diseases (CIBERER) (node U721), Spain.
authors.forename: Ismaïl
authors.initials: I
authors.lastname: Moukadiri
authors.forename: M-José
authors.initials: MJ
authors.lastname: Garzón
authors.forename: Glenn R
authors.initials: GR
authors.lastname: Björk
authors.forename: M-Eugenia
authors.initials: ME
authors.lastname: Armengod
mesh_terms: D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000737:chemistry / Q000378:metabolism*; D019875:One-Carbon Group Transferases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D012343:RNA, Transfer / Q000378:metabolism*; D012351:RNA, Transfer, Gln / Q000378:metabolism; D012356:RNA, Transfer, Leu / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D029968:Escherichia coli Proteins; C488767:MnmC protein, E coli; D009097:Multienzyme Complexes; D012351:RNA, Transfer, Gln; D012356:RNA, Transfer, Leu; D012343:RNA, Transfer; C546582:MnmG protein, E coli; D019875:One-Carbon Group Transferases; D020558:GTP Phosphohydrolases; C492932:MnmE protein, E coli