Amino acid selectivity in the aminoacylation of coenzyme A and RNA minihelices by aminoacyl-tRNA synthetases.
Coenzyme A (CoA-SH), a cofactor in carboxyl group activation reactions, carries out a function in nonribosomal peptide synthesis that is analogous to the function of tRNA in ribosomal protein synthesis. The amino acid selectivity in the synthesis of aminoacyl-thioesters by nonribosomal peptide synthetases is relaxed, whereas the amino acid selectivity in the synthesis of aminoacyl-tRNA by aminoacyl-tRNA synthetases is restricted. Here I show that isoleucyl-tRNA synthetase aminoacylates CoA-SH with valine, leucine, threonine, alanine, and serine in addition to isoleucine. Valyl-tRNA synthetase catalyzes aminoacylations of CoA-SH with valine, threonine, alanine, serine, and isoleucine. Lysyl-tRNA synthetase aminoacylates CoA-SH with lysine, leucine, threonine, alanine, valine, and isoleucine. Thus, isoleucyl-, valyl-, and lysyl-tRNA synthetases behave as aminoacyl-S-CoA synthetases with relaxed amino acid selectivity. In contrast, RNA minihelices comprised of the acceptor-TpsiC helix of tRNA(Ile) or tRNA(Val) were aminoacylated by cognate synthetases selectively with isoleucine or valine, respectively. These and other data support a hypothesis that the present day aminoacyl-tRNA synthetases originated from ancestral forms that were involved in noncoded thioester-dependent peptide synthesis, functionally similar to the present day nonribosomal peptide synthetases.
Jakubowski
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Department of Microbiology and Molecular Genetics, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, New Jersey 07103, USA. jakubows@umdnj.du
D000409:Alanine / Q000737:chemistry; D000596:Amino Acids / Q000737:chemistry*; D000604:Amino Acyl-tRNA Synthetases / Q000378:metabolism; D002855:Chromatography, Thin Layer; D003065:Coenzyme A / Q000378:metabolism* / Q000502:physiology; D004586:Electrophoresis; D004926:Escherichia coli / Q000201:enzymology; D019143:Evolution, Molecular; D007533:Isoleucine-tRNA Ligase / Q000378:metabolism; D007700:Kinetics; D007930:Leucine / Q000737:chemistry; D008250:Lysine-tRNA Ligase / Q000378:metabolism; D012313:RNA / Q000378:metabolism*; D012694:Serine / Q000737:chemistry; D013912:Threonine / Q000737:chemistry; D013997:Time Factors; D014633:Valine / Q000737:chemistry; D014637:Valine-tRNA Ligase / Q000378:metabolism
D000596:Amino Acids; D013912:Threonine; D012694:Serine; D012313:RNA; D000604:Amino Acyl-tRNA Synthetases; D007533:Isoleucine-tRNA Ligase; D008250:Lysine-tRNA Ligase; D014637:Valine-tRNA Ligase; D007930:Leucine; D014633:Valine; D000409:Alanine; D003065:Coenzyme A