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Amino acid discrimination by arginyl‐tRNA synthetases as revealed by an examination of natural specificity variants
Author(s) -
Igloi Gabor L.,
Schiefermayr Elfriede
Publication year - 2009
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2009.06866.x
Subject(s) - amino acid , transfer rna , biochemistry , chemistry , aminoacyl trna synthetase , biology , gene , rna
l ‐Canavanine occurs as a toxic non‐protein amino acid in more than 1500 leguminous plants. One mechanism of its toxicity is its incorporation into proteins, replacing l ‐arginine and giving rise to functionally aberrant polypeptides. A comparison between the recombinant arginyl‐tRNA synthetases from a canavanine producer (jack bean) and from a related non‐producer (soybean) provided an opportunity to study the mechanism that has evolved to discriminate successfully between the proteinogenic amino acid and its non‐protein analogue. In contrast to the enzyme from jack bean, the soybean enzyme effectively produced canavanyl‐tRNA Arg when using RNA transcribed from the jack bean tRNA ACG gene. The corresponding k cat / K M values gave a discrimination factor of 485 for the jack bean enzyme. The arginyl‐tRNA synthetase does not possess hydrolytic post‐transfer editing activity. In a heterologous system containing either native Escherichia coli tRNA Arg or the modification‐lacking E. coli transcript RNA, efficient discrimination between l ‐arginine and l ‐canavanine by both plant enzymes (but not by the E. coli arginyl‐tRNA synthetase) occurred. Thus, interaction of structural features of the tRNA with the enzyme plays a significant role in determining the accuracy of tRNA arginylation. Of the potential amino acid substrates tested, apart from l ‐canavanine, only l ‐thioarginine was active in aminoacylation. As it is an equally good substrate for the arginyl‐tRNA synthetase from both plants, it is concluded that the higher discriminatory power of the jack bean enzyme towards l ‐canavanine does not necessarily provide increased protection against analogues in general, but appears to have evolved specifically to avoid auto‐toxicity.