Homocysteine S-methyltransferases (HMTs) are widely distributed enzymes that convert homocysteine (Hcy) into methionine (Met) using either S-adenosylmethionine (AdoMet) or the plant secondary product S-methylmethionine (SMM) as methyl donor. AdoMet is chirally and covalently unstable, with racemization of natural (S,S)-AdoMet yielding biologically inactive (R,S)-AdoMet and depurination yielding S-ribosylmethionine (S-ribosylMet). The apparently futile AdoMet-dependent reaction of HMTs was assigned a role in repairing chiral damage to AdoMet in yeast: yeast HMTs strongly prefer (R,S)- to (S,S)-AdoMet and thereby limit (R,S)-AdoMet build-up [Vinci and Clarke (2010) J. Biol. Chem. 285, 20526–20531]. In the present study, we show that bacterial, plant, protistan and animal HMTs likewise prefer (R,S)- over (S,S)-AdoMet, that their ability to use SMM varies greatly and is associated with the likely prevalence of SMM in the environment of the organism and that most HMTs cannot use S-ribosylMet. Taken with results from comparative genomic and phylogenetic analyses, these data imply that (i) the ancestral function of HMTs was (R,S)-AdoMet repair, (ii) the efficient use of SMM reflects the repurposing of HMTs after the evolutionary advent of plants introduced SMM into the biosphere, (iii) this plant-driven repurposing was facile and occurred independently in various lineages, and (iv) HMTs have little importance in S-ribosylMet metabolism.
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Research Article|
September 22 2014
Plant-driven repurposing of the ancient S-adenosylmethionine repair enzyme homocysteine S-methyltransferase
Louis M. T. Bradbury;
Louis M. T. Bradbury
*Horticultural Sciences Department, University of Florida, Gainesville, FL 32611, U.S.A.
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Michael J. Ziemak;
Michael J. Ziemak
*Horticultural Sciences Department, University of Florida, Gainesville, FL 32611, U.S.A.
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Mona El Badawi-Sidhu;
Mona El Badawi-Sidhu
†University of California, Davis Genome Center, Davis, CA 95616, U.S.A.
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Oliver Fiehn;
Oliver Fiehn
†University of California, Davis Genome Center, Davis, CA 95616, U.S.A.
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Andrew D. Hanson
Andrew D. Hanson
1
*Horticultural Sciences Department, University of Florida, Gainesville, FL 32611, U.S.A.
1To whom correspondence should be addressed (email adha@ufl.edu).
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Publisher: Portland Press Ltd
Received:
June 16 2014
Revision Received:
July 18 2014
Accepted:
July 21 2014
Accepted Manuscript online:
July 21 2014
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© The Authors Journal compilation © 2014 Biochemical Society
2014
Biochem J (2014) 463 (2): 279–286.
Article history
Received:
June 16 2014
Revision Received:
July 18 2014
Accepted:
July 21 2014
Accepted Manuscript online:
July 21 2014
Citation
Louis M. T. Bradbury, Michael J. Ziemak, Mona El Badawi-Sidhu, Oliver Fiehn, Andrew D. Hanson; Plant-driven repurposing of the ancient S-adenosylmethionine repair enzyme homocysteine S-methyltransferase. Biochem J 15 October 2014; 463 (2): 279–286. doi: https://doi.org/10.1042/BJ20140753
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