engleski

Strutural and functional relationship among cytoplasmic and mitochondrial seryl-tRNA synthetases

The activities of two nuclearly encoded seryl-tRNA synthetases (SerRS) are required in different protein-synthesizing cell compartments of Saccharomyces cerevisiae. To investigate the mechanism of serylation, structural organization of the enzymes and the mode of substrate recognition, we have recently complemented our research on cytoplasmic enzyme by cloning and expression of the gene for mitochondrial seryl-tRNA synthetase. There is only 26 % similarity in the primary structure of two SerRS proteins. Determination of substrate binding domains by alignment guided mutagenesis, performed recently at cytoplasmic SerRS (Lenhard, B., Filipi}, S., Landeka, I., [krti}, I., Söll, D. and Weygand-\ura{evi}, I. (1997) J. Biol. Chem. 272, 1136-1141), has been extended to analyze the structure/function relationship in mitochondrial enzyme. This is of particular interest as the substrate specificities of these enzymes must differ sufficiently to foil confusion between organellar and cytoplasmic protein synthesis. The crystal structure of prokaryotic SerRS (Cusack, S., Yaremchuk, A., and Tukalo, M. (1996) EMBO J. 15, 2834-2842) allowed us to produce structural models for yeast seryl-tRNA synthatases and to place the mutations in a structural context. In conjunction with structural data for Thermus thermophilus SerRS, our kinetic experiments suggest that yeast cytoplasmic enzyme displays tRNA-dependent serine recognition, affected by the mutations in motif 2 loop residues. We are trying to elucidate whether mitochondrial SerRS structurally and functionally resembles its cytoplasmic counterpart.

aminoacyl-tRNA synthetase; tRNA

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