engleski

Emerging noncanonical functions of plant aminoacyl- tRNA synthetase

Aminoacyl-tRNA synthetases (aaRSs) participate in translation, catalyzing formation of aminoacyl- tRNAs. Many aaRSs are involved in cellular processes beyond translation but reports on noncanonical functions of plant aaRSs are scarce. We have identified protein BEN1 as protein interactor of seryl-tRNA synthetase (SerRS) from plant Arabidopsis thaliana. BEN1 is involved in metabolism of brassinosteroid hormones that regulate variety of physiological processes, including stress response. Interaction interface involves SerRS globular catalytic domain and N- terminal extension of BEN1. The partnership between SerRS and BEN1 indicates a link between protein translation and steroid metabolic pathways of the plant cell. Structural studies revealed that Arabidopsis SerRS contains intrasubunit disulfide bridge. Cysteines (at positions 213 and 244) involved in disulfide link are conserved in all SerRSs from green plants, indicating their plant- specific functional importance. In order to determine whether disulfide link plays structural or alosteric role we have substituted cysteines with serine. C213S mutant showed lower stability compared to the wild type. Unexpectedly, C244S mutant showed higher stability than wild type, while double mutant had the same stability as the wild type. Crystal structure of C244S mutant and modeled structures of two other mutants showed that number of hydrogen bonds involving residues at postions 213 and 244 correlated with protein stability. The results imply that cysteines involved in the disulfide link are important but not essential for SerRS stability. Future studies are aimed at determination of enzyme activity of the wild type and mutant proteins. Considering that disulfide bonds in cytosolic proteins are usually linked to response mechanisms to oxidative stress, the disulfide link in plant SerRSs may be involved in regulation of translation under oxidative stress conditions.

seryl-tRNA synthetase, BEN1, brassinosteroid, disulfide link

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