engleski

Molecular interactions of aminoacyl-tRNA synthetases and the ribosome

The composition and complexity of the translation machinery differ markedly between the three domains of life. Organisms from the domain Archaea show an intermediate level of complexity, sharing with eukaryotes several additional components of the translation machinery, that are absent in Bacteria. Since protein-protein interactions play a key role in numerous events that take place in a cell, most cellular processes are regulated by multiprotein complexes. Several aminoacyl-tRNA synthetases (aaRS) are located in multi-synthetase complexes (MSC) in all three domains of life. Archael seryl-tRNA synthetases (SerRSs) diverge into two major and disparate types of enzymes (bacterial and methanogenic type). We have revealed protein partners of methanogenic type SerRS in Methanothermobacter thermautotrophicus, identifying arginyl-tRNA synthetase (ArgRS) and a number of ribosomal proteins as interactors. Interaction of SerRS with ArgRS improves the activity of SerRS while the presence of SerRS did not lead to significant enhancement of ArgRS activity. This aaRSs complex may constitute a part of the thermo- and osmoadaptation mechanisms of thermophilic methanogenic Archaea, by providing an optimal microenvironment that facilitates stable tRNA aminoacylation under a range of conditions. We used the yeast two-hybrid system with several biophysical approaches to investigate interactions between aaRS and ribosomal proteins. Our results indicate that aminoacylated tRNAs to be delivered to the ribosome in the form of a ternary complex with elongation factor EF1A and GTP, may be actually generated by ribosome-bound synthetases. In support, several lines of evidence suggest that during the elongation step of translation in the cytoplasm of eukaryote cells tRNAs flow in a closed circuit. The assembly of proteins within stable or transient complexes plays an essential role in this process. The structure of M. thermautotrophicus ribosome also provides a snapshot of the reductive evolution of the archaeal ribosome and offers new insights into the evolution of the translation system in archaea. Our observations have conceptual implications for understanding how translation machinery is organized in Archaea.

aminoacyl-tRNA synthetase; translation; ribosome

nije evidentirano