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Function of the evolutionarily conserved plant methionine-S-sulfoxide reductase without the catalytic residue

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Abstract

In plants, two types of methionine sulfoxide reductase (MSR) exist, namely methionine-S-sulfoxide reductase (MSRA) and methionine-R-sulfoxide reductase (MSRB). These enzymes catalyze the reduction of methionine sulfoxides (MetO) back to methionine (Met) by a catalytic cysteine (Cys) and one or two resolving Cys residues. Interestingly, a group of MSRA encoded by plant genomes does not have a catalytic residue. We asked that if this group of MSRA did not have any function (as fitness), why it was not lost during the evolutionary process. To challenge this question, we analyzed the gene family encoding MSRA in soybean (GmMSRAs). We found seven genes encoding GmMSRAs, which included three segmental duplicated pairs. Among them, a pair of duplicated genes, namely GmMSRA1 and GmMSRA6, was without a catalytic Cys residue. Pseudogenes were ruled out as their transcripts were detected in various tissues and their Ka/Ks ratio indicated a negative selection pressure. In vivo analysis in Δ3MSR yeast strain indicated that the GmMSRA6 did not have activity toward MetO, contrasting to GmMSRA3 which had catalytic Cys and had activity. When exposed to H2O2-induced oxidative stress, GmMSRA6 did not confer any protection to the Δ3MSR yeast strain. Overexpression of GmMSRA6 in Arabidopsis thaliana did not alter the plant’s phenotype under physiological conditions. However, the transgenic plants exhibited slightly higher sensitivity toward salinity-induced stress. Taken together, this data suggested that the plant MSRAs without the catalytic Cys are not enzymatically active and their existence may be explained by a role in regulating plant MSR activity via dominant-negative substrate competition mechanism.

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Acknowledgments

This work was supported by the National Foundation for Science and Technology Development (NAFOSTED) under grant number 106-NN.02-2013.46 to DTL. We thank Vadim Gladyshev (Harvard Medical School, Boston, MA, USA) for wild-type and mutant yeast strains used in this study. Mark Dragich and Stephanie K. Dalquist are acknowledged for improving English usage in this manuscript.

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Correspondence to Dung Tien Le or Lam-Son Phan Tran.

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The authors declare that they have no conflicts of interest.

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Handling Editor: Bhumi Nath Tripathi

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Le, D.T., Nguyen, KL., Chu, H.D. et al. Function of the evolutionarily conserved plant methionine-S-sulfoxide reductase without the catalytic residue. Protoplasma 255, 1741–1750 (2018). https://doi.org/10.1007/s00709-018-1266-5

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  • DOI: https://doi.org/10.1007/s00709-018-1266-5

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