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Biochimie. 2014 May;100:18-26. doi: 10.1016/j.biochi.2013.09.027. Epub 2013 Oct 8.

Released selective pressure on a structural domain gives new insights on the functional relaxation of mitochondrial aspartyl-tRNA synthetase.

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Architecture et Réactivité de l'ARN, CNRS, Université de Strasbourg, IBMC - 15 rue René Descartes, F-67084 Strasbourg Cedex, France.
Department of Pediatrics and Child Neurology, VU University Medical Center, 1081 HV Amsterdam, The Netherlands.
Laboratoire de Spectrométrie de Masse des Interactions et des Systèmes, Chimie de la Matière Complexe, 1 rue Blaise Pascal, F-67008 Strasbourg Cedex, France.
Laboratoire de Bioinformatique et de Génomique Intégratives, IGBMC, 1 rue Laurent Fries BP-10142, F-67404 Illkirch Cedex, France.
Architecture et Réactivité de l'ARN, CNRS, Université de Strasbourg, IBMC - 15 rue René Descartes, F-67084 Strasbourg Cedex, France. Electronic address:


Mammalian mitochondrial aminoacyl-tRNA synthetases are nuclear-encoded enzymes that are essential for mitochondrial protein synthesis. Due to an endosymbiotic origin of the mitochondria, many of them share structural domains with homologous bacterial enzymes of same specificity. This is also the case for human mitochondrial aspartyl-tRNA synthetase (AspRS) that shares the so-called bacterial insertion domain with bacterial homologs. The function of this domain in the mitochondrial proteins is unclear. Here, we show by bioinformatic analyses that the sequences coding for the bacterial insertion domain are less conserved in opisthokont and protist than in bacteria and viridiplantae. The divergence suggests a loss of evolutionary pressure on this domain for non-plant mitochondrial AspRSs. This discovery is further connected with the herein described occurrence of alternatively spliced transcripts of the mRNAs coding for some mammalian mitochondrial AspRSs. Interestingly, the spliced transcripts alternately lack one of the four exons that code for the bacterial insertion domain. Although we showed that the human alternative transcript is present in all tested tissues; co-exists with the full-length form, possesses 5'- and 3'-UTRs, a poly-A tail and is bound to polysomes, we were unable to detect the corresponding protein. The relaxed selective pressure combined with the occurrence of alternative splicing, involving a single structural sub-domain, favors the hypothesis of the loss of function of this domain for AspRSs of mitochondrial location. This evolutionary divergence is in line with other characteristics, established for the human mt-AspRS, that indicate a functional relaxation of non-viridiplantae mt-AspRSs when compared to bacterial and plant ones, despite their common ancestry.


Aminoacyl-tRNA synthetase; Bioinformatics; Mitochondria; Molecular biology; Translation

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