Branched Chain Amino Acid Metabolism

描述（由申请人提供）：氨基酸除了作为蛋白质构建块的作用外，还具有重要的营养信号作用。BCAA亮氨酸是一种营养信号，可以刺激目标组织中蛋白质合成的增加，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。我们已经解决了人类线粒体BCAT （hBCATm）的几个结构，并发现它包含一个氧化还原活性二硫醇/二硫中心。CXXC中心氧化还原相关的活性调控表明，半胱氨酸残基是过氧化物感应机制的一部分，可能具有体内作用。我们发现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的。hBCATm与线粒体BCKD复合物之间的关联表明，BCAA分解代谢酶形成了称为代谢物的超分子复合物。我们将使用BCAT蛋白作为“诱饵”来验证蛋白质网控制BCAA代谢的假设，以确定BCAA代谢的蛋白质成分。确定BCAT的蛋白网，特别是神经元特异性胞质同工酶（BCATc）和新发现的人类BCATm的可选剪接形式（hBCATmsp），可能有助于鉴定这些蛋白的新功能。bcaa氧化的限速步骤在线粒体中由支链α -酮酸脱氢酶复合物（BCKD）催化。BCKD活性受Ela亚基上特定丝氨酸残基的磷酸化和去磷酸化调控。我们将确定BCATm在亮氨酸信号传导中的作用，即在大鼠体内，亮氨酸还是KIC是激活亮氨酸敏感组织mtor信号通路的信号。使用新开发的快速简单的测试系统来测量BCKD的急性调节，BCATm的作用以及亮氨酸激活mTOR信号通路与BCKD复合物（代谢）之间的联系将在体内和β细胞模型中确定。我们希望本提案提出的思想将为氨基酸代谢领域带来新的思路，并带来令人兴奋的新研究方向。

DESCRIPTION (provided by applicant): 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 (hBCATmsp), is likely to allow identification of new functions for these proteins. The rate-limiting step in BCAAoxidation 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 beta-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.