title: From one amino acid to another: tRNA-dependent amino acid biosynthesis.
abstract: Aminoacyl-tRNAs (aa-tRNAs) are the essential substrates for translation. Most aa-tRNAs are formed by direct aminoacylation of tRNA catalyzed by aminoacyl-tRNA synthetases. However, a smaller number of aa-tRNAs (Asn-tRNA, Gln-tRNA, Cys-tRNA and Sec-tRNA) are made by synthesizing the amino acid on the tRNA by first attaching a non-cognate amino acid to the tRNA, which is then converted to the cognate one catalyzed by tRNA-dependent modifying enzymes. Asn-tRNA or Gln-tRNA formation in most prokaryotes requires amidation of Asp-tRNA or Glu-tRNA by amidotransferases that couple an amidase or an asparaginase to liberate ammonia with a tRNA-dependent kinase. Both archaeal and eukaryotic Sec-tRNA biosynthesis and Cys-tRNA synthesis in methanogens require O-phosophoseryl-tRNA formation. For tRNA-dependent Cys biosynthesis, O-phosphoseryl-tRNA synthetase directly attaches the amino acid to the tRNA which is then converted to Cys by Sep-tRNA: Cys-tRNA synthase. In Sec-tRNA synthesis, O-phosphoseryl-tRNA kinase phosphorylates Ser-tRNA to form the intermediate which is then modified to Sec-tRNA by Sep-tRNA:Sec-tRNA synthase. Complex formation between enzymes in the same pathway may protect the fidelity of protein synthesis. How these tRNA-dependent amino acid biosynthetic routes are integrated into overall metabolism may explain why they are still retained in so many organisms.
authors.affiliation: Department of Molecular Biophysics, Yale University, New Haven, CT 06520-8114, USA.
authors.forename: Kelly
authors.initials: K
authors.lastname: Sheppard
authors.forename: Jing
authors.initials: J
authors.lastname: Yuan
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Hohn
authors.forename: Brian
authors.initials: B
authors.lastname: Jester
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Devine
authors.forename: Dieter
authors.initials: D
authors.lastname: Söll
mesh_terms: D000604:Amino Acyl-tRNA Synthetases / Q000737:chemistry / Q000378:metabolism; D001216:Asparagine / Q000096:biosynthesis*; D003545:Cysteine / Q000096:biosynthesis*; D005973:Glutamine / Q000096:biosynthesis*; D019884:Nitrogenous Group Transferases / Q000737:chemistry / Q000378:metabolism; D010770:Phosphotransferases / Q000737:chemistry / Q000378:metabolism; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism*; D017279:Selenocysteine / Q000096:biosynthesis*
chemical_list: D012346:RNA, Transfer, Amino Acyl; C483187:glutamyl-tRNA(Gln); C112705:selenocysteinyl-tRNA; D017279:Selenocysteine; D005973:Glutamine; D001216:Asparagine; D019884:Nitrogenous Group Transferases; D010770:Phosphotransferases; D000604:Amino Acyl-tRNA Synthetases; D003545:Cysteine