Laboratoire d'Enzymologie et Biochimie Structurales, C.N.R.S., 1 Avenue de la Terrasse, 91190 Gif-sur-Yvette, France.
Methionyl-tRNA synthetase (MetRS) is a multidomain protein that specifically binds tRNA(Met) and catalyzes the synthesis of methionyl-tRNA(Met). The minimal, core enzyme found in Aquifex aeolicus is made of a catalytic domain, which catalyzes the aminocylation reaction, and an anticodon-binding domain, which promotes tRNA-protein association. In eukaryotes, additional domains are appended in cis or in trans to the core enzyme, and increase the stability of the tRNA-protein complexes. Eventually, as observed for MetRS from Homo sapiens, the C-terminal appended domain causes a slow release of aminoacyl-tRNA, and establishes a limiting step in the global aminoacylation reaction. Here, we report that MetRS from the nematode Caenorhabditis elegans displays a new type of structural organization. Its very C-terminal appended domain is related to the oligonucleotide binding (OB)-fold based tRNA-binding domain recovered at the C-terminus of MetRS from plant but, in the nematode enzyme, this domain is separated from the core enzyme by an insertion domain. Gel retardation and tRNA aminoacylation experiments show that MetRS from nematode is functionally related to human MetRS despite the fact that their appended tRNA-binding domains have distinct structural folds, and are not orthologs. Thus, functional convergence of human and nematode MetRS is the result of parallel and convergent evolution that might have been triggered by the selective pressure to invent processivity of tRNA handling in translation in higher eukaryotes.
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on November 19, 2010
