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University of Western Ontario

1. Joshi, Jaya. Deciphering Sulfur Amino Acid Metabolism in Developing Seeds of Common Bean.

Degree: 2017, University of Western Ontario

With increasing food insecurity in the populated world, the number of people affected by chronic undernourishment is also increasing. Alone, protein energy malnutrition is linked to 6 million deaths annually. Despite being a good source of protein and dietary fibre, the quality of bean protein is limited because of sub optimal levels of essential sulfur amino acids: methionine and cysteine. Levels of cysteine and methionine in developing seeds have an inverse relationship with the non-protein sulfur amino acid S-methyl-cysteine (S-methylCys) and dipeptide g-glutamyl-S-methyl-cysteine (g-Glu-S-methylCys). One of the strategies to improve protein quality in bean is to redirect sulfur from S-methylCys and g-Glu-S-methylCys to the cysteine pool. In this thesis, elucidation of the unknown biochemical pathway of S-methylCys synthesis was accomplished using 13C and 15N labelled serine and cysteine, and revealed serine as the precursor of S-methylCys biosynthesis. Feeding developing seeds with 13C and 15N labelled methionine also suggested a role for methionine in S-methylCys biosynthesis. In the cytosol, methanethiol released during hydrolysis of methionine condensed with O-acetylserine to form S-methylCys. BSAS4;1, a b-substituted alanine synthase family member plays a key role in this reaction. BSAS4;1 is a cysteine synthase that utilizes O-acetylserine as a carbon backbone donor and methionine as a methyl donor to synthesize S-methylCys. In the case of g-Glu-S-methylCys, another pathway seems more active, whereby homoglutathione is transformed into S-methylhomoglutathione and g-Glu-S-methylCys is synthesized in the presence of a carboxypeptidase. This study identifies BSAS4;1 and methionine g-lyase (MGL) as candidate enzymes for S-methylCys biosynthesis in common bean. According to the Canadian Food Inspection Agency, only the label “Good source of protein” can be used for beans and other legumes. In future, silencing of the S-methylCys pathway candidate genes or development of TILLING lines with high cysteine and methionine levels may change bean from a good source to an “excellent source of protein”. Ultimately, the findings of this thesis could provide a helping hand to overcome the food insecurity in the growing world.

Subjects/Keywords: Sulfur amino acids; cysteine; methionine; S-methyl-cysteine; gamma-glutamyl-S-methylcysteine; isotope labelling; S-methylhomoglutathione; common bean; Biochemistry; Biotechnology; Plant Biology

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Joshi, J. (2017). Deciphering Sulfur Amino Acid Metabolism in Developing Seeds of Common Bean. (Thesis). University of Western Ontario. Retrieved from http://ir.lib.uwo.ca/etd/4858

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Joshi, Jaya. “Deciphering Sulfur Amino Acid Metabolism in Developing Seeds of Common Bean.” 2017. Thesis, University of Western Ontario. Accessed September 20, 2017. http://ir.lib.uwo.ca/etd/4858.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Joshi, Jaya. “Deciphering Sulfur Amino Acid Metabolism in Developing Seeds of Common Bean.” 2017. Web. 20 Sep 2017.

Vancouver:

Joshi J. Deciphering Sulfur Amino Acid Metabolism in Developing Seeds of Common Bean. [Internet] [Thesis]. University of Western Ontario; 2017. [cited 2017 Sep 20]. Available from: http://ir.lib.uwo.ca/etd/4858.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Joshi J. Deciphering Sulfur Amino Acid Metabolism in Developing Seeds of Common Bean. [Thesis]. University of Western Ontario; 2017. Available from: http://ir.lib.uwo.ca/etd/4858

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

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