Branched Chain Amino Acid Metabolism

除了作为蛋白质组成单元的作用外，氨基酸还具有重要的营养信号作用。 支链氨基酸亮氨酸是一种营养信号，可以刺激靶组织蛋白质合成增加，它的作用是 我们的假设是亮氨酸信号与亮氨酸代谢有关。分解代谢途径的第一步 是由支链转氨酶同工酶(BCAT)催化的可逆转氨化反应。我们有 解决了人类线粒体BCAT(HBCATm)的几种结构，并发现它包含一个 氧化还原活性二硫醇/二硫键中心。CXXC中心对活动的氧化还原相关调节 证明半胱氨酸残基是过氧化氢感应机制的一部分，在体内可能有 角色。我们发现hBCATm可以与BCKD复合体结合，这种相互作用是 对氧化还原反应敏感。HBCATm和线粒体BCKD复合体之间的关联表明 支链氨基酸分解酶形成超分子复合体，称为新陈代谢。我们将检验这一假设 蛋白质网控制支链氨基酸的代谢，使用BCAT蛋白作为“诱饵”来识别 BCAA代谢物。BCAT蛋白质网的测定，特别是神经元特异性蛋白质网的测定 胞浆同工酶(BCATC)和新发现的人BCATm的选择性剪接形式(hBCATm- SP)，很可能有助于鉴定这些蛋白质的新功能。BCAA中的速率限制步骤 线粒体的氧化是由支链α-酮酸脱氢酶催化的。 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在亮氨酸信号转导中的作用，即 亮氨酸或KIC是激活体内亮氨酸敏感组织中mTOR信号通路的信号 那只老鼠。使用一种新开发的快速简单的测试系统来测量BCKD的急性调节， BCATm在mTOR信号通路亮氨酸激活与BCKD复合体中的作用及联系 (代谢)将在体内和13细胞模型中确定。我们希望本报告中提出的想法 提案将为氨基酸代谢领域带来新的思维方式，并将带来令人兴奋的新 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.