From one amino acid to another: tRNA-dependent amino acid biosynthesis.
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.
Sheppard
Kelly
K
Department of Molecular Biophysics, Yale University, New Haven, CT 06520-8114, USA.
Yuan
Jing
J
Hohn
Michael J
MJ
Jester
Brian
B
Devine
Kevin M
KM
Söll
Dieter
D
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*
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