engleski

Dynamics of an aminoacyl-tRNA synthetase complex assembly: switching between canonical and ancillary roles

Every cell depends on meticulous decoding of its genetic material in order to reproduce its finely tuned proteinaceous machinery. This fidelity of protein biosynthesis is preserved by accurate aminoacylation of a specific transfer RNA (tRNA) with a cognate amino acid, and the ribosomal decoding of each tRNA in accord with messenger RNA (mRNA) codons. The first reaction is catalyzed by a set of enzymes known as aminoacyl-tRNA synthetases (aaRS). Proteins participate in discrete functions, but also cooperate and interact, usually with a direct functional consequence. AaRSs assemble into multisynthetase complexes (MSC) with a stoichiometry and composition depending on the organism. MSCs are implicated in wide variety of processes, such as splicing, apoptosis, transcriptional regulation etc. We have previously reported the existence of such complex in a methanogenic archaeon Methanothermobacter thermoautothophicus. This transient complex consists of two aaRSs, atypical seryl- and arginyl-tRNA synthetase (ArgRS and SerRS, respectively). In order to structurally characterize this interaction, distinct regions of the archaeal ArgRS were removed and truncated variants of the enzyme constructed. Removal of the C-terminal portion of the enzyme had a deleterious effect on its stability. In contrast, elimination of the N- terminal region yielded a soluble protein almost incapable for SerRS binding. The mutant ArgRS also showed decreased capacity to aminoacylate cognate tRNA, which was to be expected due to this domain’s involvement in cognate tRNA recognition. In order to determine which elements of the aforementioned domain have the greatest impact on the complex stability further topological analysis was introduced. Interestingly, SerRS binding propensity decreased gradually with N-terminus’ shortening, implicating that this tRNA binding element serves also as a SerRS docking platform. Only element with insignificant contribution to SerRS binding was found to be helix H1 which folds away from the tRNA binding interface. Implication that SerRS and arginine tRNA (tRNAArg) recognize not only the same region, but also the same surface residues of ArgRS was further demonstrated by competitive behaviour of tRNAArg and SerRS toward ArgRS binding. Since cellular homeostasis directly depends on aaRS’s activity, this selective switching of ArgRS between its canonical and ancillary roles might delineate a mechanism of a prokaryotic translational control.

aminoacyl-tRNA synthetase; tRNA; protein-protein interaction; translational control

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