Evolutionary aspects of accuracy of phenylalanyl-tRNA synthetase. Accuracy of the cytoplasmic and chloroplastic enzymes of a higher plant (Phaseolus vulgaris)

Abstract

The phenylalanyl-tRNA synthetases from cytoplasm and chloroplasts of bean (Phaseolus vulgaris) leaves employ different strategies with respect to accuracy. The chloroplastic enzyme that is coded for by the nuclear genome follows the pathway of posttransfer proofreading, also characteristic for enzymes from eubacteria and cytoplasm and mitochondria of lower eukaryotic organisms. In contrast, the cytoplasmic enzyme uses pretransfer proofreading in the case of noncognate natural amino acids, characteristic for higher eukaryotic organisms and archaebacteria. Dependent on the nature of the noncognate amino acid, pretransfer proofreading in this case occurs without tRNA stimulation or with tRNA stimulated with no or little effect of the nonaccepting 3'-OH group of the terminal adenosine. The fundamental mechanistic difference in proofreading between the heterotopic intracellular isoenzymes of the plant cell supports the idea of the origin of the chloroplastic gene by gene transfer from a eubacterial endosymbiont to the nucleus. Origin by duplication of the nuclear gene, as indicated for mitochondrial phenylalanyl-tRNA synthetases [Gabius, H.-J., Engelhardt, R., Schroeder, F.R., & Cramer, F. (1983) Biochemistry 22, 5306-5315], appears unlikely. Further analyses of the ATP/PPi pyrophosphate exchange and aminoacylation of tRNAPhe-C-C-A(3'NH2), using 11 phenylalanine analogues, reveal intraspecies and interspecies variability of the architecture of the amino acid binding part within the active site.

Seryl-tRNA Synthetases in Translation and Beyond

“…Proofreading activities were shown for only few plant aaRSs. [92][93][94] Findings that yeast and archaeal SerRSs showed low or moderate misactivation of near-cognate amino acids and serine analogue SerHX [28,55,95] prompted us to explore the fidelity of the maize cytosolic and dually targeted organellar SerRSs, [67] Organellar SerRS exhibited higher discrimination against threonine, cysteine and SerHX as compared to its cytosolic counterpart. Both enzymes showed pre-transfer editing activity towards tested compounds implying their high overall accuracy.…”

Aminoacylation inSulfolobus acidocaldariusand in methanogenic and halophilic archaebacteria

“…Depending on the object under investigation, archaebacteria either exhibit unique features or resemble more closely eubacteria or eukaryotes [2,4]. Since aminoacylation of tRNA with protein synthesis is a central process in all primary kingdoms and has already been established in the putative ancestor of the different lineages, the progenote, structural, functional and immunological comparison of PRS from different organisms has provided interesting insights into the evolutionary history of this type of enzyme [5][6][7][8]. We have now extended this study to an enzyme from a sulphur-metabolizing archaebacterium.…”