Doctoral Training/Biochemistry/Transsulfuration Enzymes

描述（由申请人提供）：该项目的长期目标是了解催化半胱甘肽周围反应的酶的结构和功能关系，半胱甘肽是半胱氨酸和同型半胱氨酸相互转化的反式硫化途径中的中心中间体。反式硫化酶在为生长提供半胱氨酸和蛋氨酸以及调节这些氨基酸的体内平衡中起着重要作用。人类的某些遗传疾病，如同型半胱氨酸血症，是由这些酶的基因突变引起的。项目的具体目的是表征遗传模式植物拟南芥（Arabidopsis thaliana）基因座At1g33320编码的基因的酶功能和生理作用。基于序列同源性，该基因被认为编码一种碳氧裂解酶——半胱硫氨酸γ合成酶。然而，初步证据表明，它的功能是胱氨酸β -裂解酶，一种碳-硫酪氨酸酶。这一假设将通过进行体外酶动力学实验来检验，并通过使用遗传互补测试来检验酶在体内条件下的功能。该基因产物的生理作用也将通过研究其表达、亚细胞定位和检查基因敲除突变引起的表型来探索。

DESCRIPTION (provided by applicant): The broad, long-term objective of the project is to understand the structure and function relationship of enzymes that catalyze reactions around cystathione, a central intermediate in the trans-sulfuration pathways that inter-convert cysteine and homocysteine. The trans-sulfuration enzymes play important roles in supplying cysteine and methionine for growth and in regulating the homeostasis of these amino acids. Certain genetic diseases in humans, such as homocysteinemia, are caused by mutations in the genes for these enzymes.The specific aim of project is to characterize the enzymatic function and physiological role of a gene encoded by locus At1g33320 of the genetic model plant Arabidopsis thaliana. Based on sequence homology this gene was proposed to encode cystathionine gamma-synthase, a carbon-oxygen lyase. However, preliminary evidence suggests that it functions as cystathionine beta-lyase, a carbon-sulfur tyase. This hypothesis will be examined by carrying out in vitro enzyme kinetic experiments, and by examining the function of the enzyme under in vivo conditions using a genetic complementation test. The physiological role of the gene product will also be explored by studying its expression, its subcellular localization, and by examining the phenotype resulting from knock-out mutation of the gene.