AlaX is the homologue of the class II alanyl-tRNA synthetase editing domain and has been shown to exhibit autonomous editing activity against mischarged tRNAAla. Here, we present the structures of AlaX from the archaeon Pyrococcus horikoshii in apo form, complexed with zinc, and with noncognate amino acid L-serine and zinc. Together with mutational analysis, we demonstrated that the conserved Thr-30 hydroxyl group located near the β-methylene of the bound serine is responsible for the discrimination of noncognate serine from cognate alanine, based on their chemical natures. Furthermore, we confirmed that the conserved Gin-584 in alanyl-tRNA synthetase, which corresponds to Thr-30 of AlaX, is also critical for discrimination. These observations strongly suggested conservation of the chemical discrimination among trans- and cis-editing of tRNAAla.
|Number of pages||6|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|Publication status||Published - Aug 16 2005|
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