engleski

Possible quality control mechanisms in seryl-tRNA formation

The high level of translational fidelity is ensured by various types of quality control mechanisms, which are adapted to prevent or correct naturally occurring mistakes. Accurate aminoacyl-tRNA synthesis is mostly dependent on the specificity of the aaRSs, i.e. their ability to choose between competing structurally similar substrates. Our studies have revealed that accurate seryl-tRNA synthesis in yeast and plants is accomplished via tRNA-assisted optimization of amino acid binding to the enzyme active site (1,2). Based on our recent kinetic data, a mechanism is proposed by which transient protein:RNA complex activates the cognate amino acid more efficiently and more specifically than the apoenzyme alone. This may proceed via a tRNA-induced conformational change in the enzyme’s active site. As shown by the truncation of tRNA at the 3’-end, terminal adenosine is not important in effecting the rearrangement of the serine binding site. The influence of 3’-truncated tRNASer on the activation of serine by SerRS variants mutated in the active site is much less pronounced. These mutants also misactivate structurally similar threonine, indicating that amino acid substitutions in the active site interfere with the ability of the synthetase to discriminate against noncognate substrates. Slighter misactivation of threonine was also observed by wild type SerRS. The presence of tRNASerCC reduces threonyl-adenylate formation. Thus, the sequence-specific tRNA:synthetase interactions enhance discrimination of the amino acid substrates by yeast SerRS. Different quality control mechanism in tRNA serylation may be related to the complex formation between SerRS and a nonsynthetase protein. The interaction between yeast SeRS and peroxin Pex21p has been identified in yeast, by using the two-hybrid screen. This was confirmed by an in vitro binding assay with truncated Pex21p fused to glutathione-S-transferase. Experiments revealing potential relevance of this unusual interaction in enhancing the specificity of substrate recognition are in progress. (1) Lenhard, B., Filipic, S., Landeka, I., Skrtic, I., Söll, D. and Weygand-Durasevic, I., J. Biol. Chem. 272 (1997) 1136-1141. (2) Rokov Plavec, J., Mustra, S., Landeka, I., Mijakovic, I. and Weygand-Durasevic, I., Arch. Biochem. Biophys. 397 (2002) 40-50.

aminoacil-tRNA-sintetaze; kontrola kvalitete u biosintezi proteina

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