Biochemistry and genetics of sulfur amino acid metabolism

我的长期研究目标包括了解半胱氨酸和蛋氨酸生物合成途径的调控，以及催化这两种含硫氨基酸相互转化的转硫途径中酶的底物和反应特异性的基础。这项研究包括三个相互关联的项目，涉及生物技术、农业和环境应用。(1)在下一个授权周期中，我和我的学生将继续研究转硫途径中结构相似但机械不同的酶。从这项工作中确定这些酶的反应特异性决定因素，将有助于我们了解吡哆醛5'-磷酸依赖酶如何控制这种催化多功能辅助因子的化学反应，从而促进定制生物催化剂的设计，用于生产新的氨基酸化合物。谷物豆类是加拿大重要的出口作物和许多国家的主食。然而，从人体营养的角度来看，它们缺乏必需氨基酸蛋氨酸。我的实验室正在探索鹰嘴豆蛋氨酸生物合成途径中代谢物流动的调节机制。这项工作的结果将使谷物豆类的精细基因工程成为可能，以提高其营养品质。(3)氨基酸半胱氨酸和蛋氨酸是谷胱甘肽、植物螯合素和烟胺等化合物的前体，能协调重金属离子在植物体内的转运和固存。保守估计，加拿大有3万个受污染地点，这表明迫切需要开发低成本的补救技术。我的实验室正在探索镉暴露对高富集物种芥菜中硫同化和代谢途径基因表达水平的影响，这些途径产生富含硫的化合物，可以螯合重金属。鉴定与超积累有关的基因将有助于设计具有更好植物修复能力的植物品种。

The long-term goals of my research program include understanding the regulation of the pathways of cysteine and methionine biosynthesis and the basis of substrate and reaction specificity in the enzymes of the transsulfuration pathways, which catalyze the inter-conversion of these two sulfur-containing amino acids. This research encompasses three inter-related projects with biotechnological, agricultural and environmental applications. (1) During the next granting cycle, my students and I will continue to investigate the structurally-similar, but mechanistically-distinct enzymes of the transsulfuration pathways. The identification of determinants of reaction specificity in these enzymes, resulting from this work, will contribute to our understanding of how pyridoxal 5'-phosphate-dependent enzymes control the chemistry of this catalytically-versatile cofactor, thereby facilitating the design of customized biocatalysts for the production of novel amino acid compounds. (2) Grain legumes are important Canadian export crops and staple foods in many countries. However, they are deficient in the essential amino acid methionine, from the perspective of human nutrition. My lab is exploring the mechanisms that regulate the flow of metabolites in the methionine biosynthetic pathway of chickpea. The results of this work will enable the subtle genetic engineering of grain legumes required to improve their nutritional quality. (3) The amino acids cysteine and methionine are the precursors of compounds, such as glutathione, phytochelatins and nicotianamine, which can coordinate heavy metal ions and are involved in their translocation and sequestration in plants. The conservative estimate of 30,000 contaminated sites in Canada demonstrates the urgent need for developing low-cost remediation technologies. My lab is exploring the effect of cadmium exposure on the expression levels of genes of the sulfur assimilation and metabolism pathways, which produce sulfur-rich compounds that chelate heavy metals, in the hyperaccumulator species Brassica juncea. The identification of genes linked to hyperaccumulation will facilitate the design of plant varieties with improved capacity for phytoremediation.