Doctoral Training/Biochemistry/Transsulfuration Enzymes

描述(申请人提供)：该项目广泛的、长期的目标是了解催化围绕半胱氨酸和同型半胱氨酸的反应的酶的结构和功能关系，胱硫酮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。反式硫化酶在提供生长所需的半胱氨酸和蛋氨酸以及调节这些氨基酸的动态平衡方面起着重要作用。人类的某些遗传性疾病，如同型半胱氨酸血症，是由这些酶的基因突变引起的。该项目的具体目的是表征遗传模式植物拟南芥AT1g33320基因座编码的基因的酶功能和生理作用。根据序列同源性，该基因被认为编码了一种碳-氧裂解酶--胱硫醚-γ-合成酶。然而，初步证据表明，它的功能是胱硫醚β-裂解酶，一种碳-硫类型酶。这一假说将通过进行体外酶动力学实验，并通过使用遗传互补测试在体内条件下检查酶的功能来验证。基因产物的生理作用也将通过研究它的表达，它的亚细胞定位，以及通过检测基因敲除突变导致的表型来探索。

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.