Evolutionary aspects of accuracy of phenylalanyl-tRNA synthetase. Accuracy of fungal and animal mitochondrial enzymes and their relationship to their cytoplasmic counterparts and a prokaryotic enzyme

Abstract

Phenylalanyl-tRNA synthetases from mitochondria of yeast and hen liver resemble their corresponding cytoplasmic counterparts. Whereas slight intraspecies differences at the amino acid binding site, reflecting variations in the structures of these distinct enzymes, are exploitable by phenylalanine analogues, no intraspecies difference can be noted for the strategies to achieve the high fidelity of protein synthesis. While the yeast mitochondrial enzyme follows the pathway of posttransfer proofreading, the hen liver mitochondrial enzyme uses a tRNA-dependent pretransfer proofreading in the case of the natural amino acids. The accuracy of mitochondrial phenylalanyl-tRNA synthetases appears to be even better than the accuracy of the corresponding cytoplasmic enzymes. Interspecies rather than intraspecies differences for the functional role of certain amino acid residues of the enzymes further indicate the close relationship of the intracellular heterotopic isoenzymes. By use of a highly sensitive immunospotting procedure, common antigenic determinants are detected only within the enzymes from the two intracellular compartments of the same organism. The results suggest the origin of the cytoplasm-mitochondrion isoenzyme pair by independent gene duplication of the ancestral nuclear gene. A similarity of mitochondrial enzymes to the phenylalanyl-tRNA synthetase from Escherichia coli is not observed.

Post-transfer editing in vitro and in vivo by the β subunit of phenylalanyl-tRNA synthetase

“…Mitochondrial PheRS is a chimera of the canonical a subunit with a C-terminal appendage containing the tRNA anticodon-binding domain (B8) of the canonical b subunit, but no putative editing domain. It was originally proposed that mitochondrial PheRSs are active in editing (Gabius et al, 1983), although later studies questioned the quality of the enzymes used in these studies (Sanni et al, 1991). Mitochondrial amino-acid pools are believed to be similar to those in the cytoplasm (Costantino and Attardi, 1973), suggesting that the need for editing mischarged Tyr would be similar in both compartments.…”

Loss of Editing Activity during the Evolution of Mitochondrial Phenylalanyl-tRNA Synthetase

“…Despite their similarity to bacterial PheRSs, the mitochondrial versions do not contain regions analogous to the known editing domain (25). Although it was originally suggested that mitochondrial PheRSs were active in editing (28), later studies questioned the purity of the enzymes used for these studies (26). Here we describe an investigation of amino acid specificity and editing by mitochondrial and cytosolic PheRSs from the yeast Saccharomyces cerevisiae.…”

Striking differences of physical properties for two different phenylalanyl-tRNA synthetases in Cyanophora paradoxa

“…These activities are readily separated by salting-out chromatography, and have a significantly different M r, which is not due to proteolytic degradation or partial dissociation under the conditions of gel filtration. Regarding the problem of the origin of cyanelles and plastids, this detection of 2 significantly distinct PRS involved in the expression of the 2 genomes within C. paradoxa is of considerable potential in establishing phylogenetic relationships, as described earlier using this system for yeast and liver mitochondria [8]. Considering the substrate specificity, it is thus reasonable to view the enzyme with M r 80 000 as a cyanelle enzyme.…”

“…Due to the fundamental role of PRS in protein biosynthesis, comparative studies on PRS have been used to trace the evolutionary process in other organisms [7][8][9]. We therefore initiated a study on the PRS activities found in C. paradoxa.…”