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Insights into substrate promiscuity of human seryl-tRNA synthetase.

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posted on 19.06.2018, 00:00 by Kaitlyn M. Holman, Anupama K. Puppala, Jonathan W. Lee, Hyun Lee, Miljan Simonovic
Seryl-tRNA synthetase (SerRS) attaches L-serine to the cognate serine tRNA (tRNASer) and the noncognate selenocysteine tRNA (tRNASec). The latter activity initiates the anabolic cycle of selenocysteine (Sec), proper decoding of an in-frame Sec UGA codon, and synthesis of selenoproteins across all domains of life. While the accuracy of SerRS is important for overall proteome integrity, it is its substrate promiscuity that is vital for the integrity of the selenoproteome. This raises a question as to what elements in the two tRNA species, harboring different anticodon sequences and adopting distinct folds, facilitate aminoacylation by a common aminoacyl-tRNA synthetase. We sought to answer this question by analyzing the ability of human cytosolic SerRS to bind and act on tRNASer, tRNASec, and 10 mutant and chimeric constructs in which elements of tRNASer were transposed onto tRNASec We show that human SerRS only subtly prefers tRNASer to tRNASec, and that discrimination occurs at the level of the serylation reaction. Surprisingly, the tRNA mutants predicted to adopt either the 7/5 or 8/5 fold are poor SerRS substrates. In contrast, shortening of the acceptor arm of tRNASec by a single base pair yields an improved SerRS substrate that adopts an 8/4 fold. We suggest that an optimal tertiary arrangement of structural elements within tRNASec and tRNASer dictate their utility for serylation. We also speculate that the extended acceptor-TΨC arm of tRNASec evolved as a compromise for productive binding to SerRS while remaining the major recognition element for other enzymes involved in Sec and selenoprotein synthesis.


We thank the staff of the Research Resource Center (UIC-RRC) for their help with SPR data acquisition and Prof. Alexander Mankin and James Marks (UIC) for help with aminoacylation assays. The National Institute of General Medical Sciences grant (GM097042 to MS), the UIC Chancellor’s Undergraduate Research Award (to JWL), the UIC Honors College Research Grant (to JWL), the UIC CCTS Pre-doctoral Education for Clinical and Translational Scientists Fellowship (to AKP) and the UIC Provost Deiss Award (to AKP) supported this work.


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Holman, K. M., Puppala, A. K., Lee, J. W., Lee, H. and Simonovic, M. Insights into substrate promiscuity of human seryl-tRNA synthetase. RNA. 2017. 23(11): 1685-1699. 10.1261/rna.061069.117


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