Branched Chain Amino Acid Metabolism

除了作为蛋白质构建模块的作用外，氨基酸还作为营养信号发挥重要作用。 BCAA亮氨酸是一种营养信号，刺激靶组织中蛋白质合成增加， 我们假设亮氨酸信号与亮氨酸代谢有关。分解代谢途径的第一步 是由支链氨基转移酶同工酶（BCAT）催化的可逆转氨作用。我们有 解决了人类线粒体BCAT（hBCATm）的几种结构，并发现它含有一个 氧化还原活性二硫醇/二硫化物中心。CXXC中心对活性的氧化还原相关调节 表明半胱氨酸残基是过氧化物敏感机制的一部分， 作用我们已经发现hBCATm可以与BCKD复合物结合，并且这种相互作用是 氧化还原敏感。hBCATm和线粒体BCKD复合物之间的关联表明， 支链氨基酸分解代谢酶形成超分子复合物称为代谢子。我们将检验这个假设， 一个蛋白质网络控制支链氨基酸代谢，使用BCAT蛋白作为“诱饵”，以确定蛋白质组分， BCAA代谢物。确定BCAT的蛋白质网，特别是神经元特异性 胞质同工酶（BCATc）和新识别的人BCATm的可变剪接形式（hBCATm-1）。 sp），可能允许鉴定这些蛋白质的新功能。支链氨基酸的限速步骤 氧化在线粒体中由支链α-酮酸脱氢酶催化 复合体（BCKD）。BCKD活性受特定丝氨酸的磷酸化和去磷酸化调节 Ela亚基上的残基。我们将确定BCATm在亮氨酸信号传导中的作用，即， 亮氨酸或KIC是在体内激活亮氨酸敏感组织中mTOR信号传导途径的信号， 老鼠使用新开发的快速和简单的测试系统来测量BCKD的急性调节， BCATm的作用以及mTOR信号通路的亮氨酸激活与BCKD复合体之间的联系 将在体内和在13细胞模型中测定（代谢）。我们希望，本报告中提出的想法 该提案将为氨基酸代谢领域带来新的思维方式，并将导致令人兴奋的新 研究方向。

In addition to their role as protein building blocks, amino acids have a significant role as nutritional signals. The BCAA leucine is a nutrient signal that stimulates increased protein synthesis in target tissues, and it Js our hypothesis that leucine signaling is linked to leucine metabolism. The first step in the catabolic pathway is reversible transamination catalyzed by the branched chain aminotransferase isozymes (BCAT). We have solved several structures of the human mitochondrial BCAT (hBCATm) and discovered that it contains a redox-active dithiol/disulfide center. The redox-linked regulation of activity by the CXXC center demonstrates that the cysteine residues are part of a peroxide-sensing mechanism that may have an in vivo role. We have discovered that hBCATm can associate with the BCKD complex and that this interaction is redox sensitive. The association between hBCATm and the mitochondrial BCKD complex suggests that BCAA catabolic enzymes form supramolecular complex called a metabolon. We will test the hypothesis that a protein web controls BCAA metabolism using the BCAT proteins as "bait" to identify protein components of the BCAA metabolon. Determination of the protein web for the BCAT, particularly of the neuron-specific cytosolic isozyme (BCATc) and a newly recognized alternatively spliced form of human BCATm (hBCATm- sp), is likely to allow identification of new functions for these proteins. The rate-limiting step in BCAA oxidation is catalyzed in mitochondria by the branched-chain alpha-keto acid dehydrogenase enzyme complex (BCKD). BCKD activity is regulated by phosphorylation and dephosphorylation of a specific serine residue on the Ela subunit. We will determine the role of BCATm in leucine signaling, that is, whether leucine or KIC is the signal that activates the mTOR-signaling pathway in leucine-sensitive tissues in vivo in the rat. Using a newly developed rapid and simple test system to measure acute regulation of BCKD, the role of BCATm and link between leucine activation of the mTOR signaling pathway and BCKD complex (metabolism) will be determined in vivo and in a 13-cell model. It is our hope that the ideas put forth in this proposal will bring new ways of thinking into the field of amino acid metabolism and will lead to exciting new research directions.