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Plant seryl-tRNA synthetase as a link between translation and metabolism of brassinosteroid hormones

Aminoacyl-tRNA synthetases (aaRSs) are essential cellular enzymes that covalently link specific amino acid to the cognate tRNA, thereby acting as translators of the genetic code. Many aaRSs are involved in diverse cellular processes beyond translation, acting alone or in complex with other proteins. However, studies of aaRS assemblies and noncanonical functions in plants are scarce, as are structural studies of plant aaRSs. We have solved the crystal structure of Arabidopsis thaliana cytosolic seryl-tRNA synthetase (SerRS), which is the first crystallographic structure of a plant aaRS [1]. Arabidopsis SerRS displays structural features typical of canonical SerRSs, except for a unique intrasubunit disulfide bridge. Interestingly, cysteines involved in disulfide link are conserved in all SerRSs from green plants, indicating their plant-specific functional importance. In order to identify protein interactors of Arabidopsis SerRS, we performed yeast two hybrid screen and identified BEN1, protein involved in metabolism of steroidal plant hormones brassinosteroids that regulate a variety of physiological processes crucial for normal plant growth and development. The SerRS:BEN1 interaction was confirmed using surface plasmon resonance and microscale thermophoresis (MST). To pinpoint regions responsible for interaction, truncated variants of SerRS and BEN1 were created and analyzed using MST. Detailed analysis showed that interaction interface involves SerRS globular catalytic domain and the acidic N-terminal extension of BEN1 protein. BEN1 does not have a strong impact on SerRS aminoacylation activity, indicating that the primary function of the complex is not the modification of SerRS canonical activity. Perhaps SerRS performs as yet unknown noncanonical functions mediated by BEN1. The SerRS:BEN1 complex is a rare example of an aaRSs interacting with an enzyme involved in primary or secondary metabolism. The partnership between SerRS and BEN1 indicates a link between protein translation and steroid metabolic pathways of the plant cell [1]. [1] Kekez et al, FEBS J, 2019, 286, 536.

aminoacyl-tRNA synthetase ; translation ; protein interaction ; crystal structure ; disulfide link ; BEN1 ; brassinosteroids

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