Regulation of Coenzyme A Levels by Panothenate Kinase

描述(申请人提供)：辅酶A(CoA)是生物学中主要的酰基载体，也是中间代谢的重要辅因子。游离型辅酶A(非酰化)及其硫代酯是变构配体，通过关键的代谢酶控制碳流，进而控制能量的产生。有充分的证据表明，细胞内CoA水平随着激素、饮食和药物的变化而波动，并且在糖尿病等代谢紊乱中处于失调状态。辅酶A是从维生素泛酸开始的一系列普遍的反应产生的，通过这一途径的流量由第一种酶-泛酸激酶(Pank)控制。哺乳动物有多种Pank酶，每一种都有独特的调节特性、表达模式和细胞内分布。Pank在新陈代谢中的重要性已经在原核系统中得到了广泛的验证，但我们对Pank的生化调节和多种哺乳动物Pank酶在代谢生理控制中的作用的了解还存在很大差距。随着人类PANK2基因突变与一种称为PKAN的进行性神经疾病的关联的发现，这些酶的重要性在哺乳动物系统中受到了尖锐的关注。人类PanK2同工酶与线粒体相关。最初的想法是，所有致病突变都使PanK2酶功能失活；然而，我们的综合分析表明，很大一部分突变不会使PanK2失活，这表明这些错义突变改变了蛋白质的一个重要调节功能。我们认为，线粒体Pank在CoA水平对利用脂肪酸作为燃料的代谢适应中具有独特的调节作用。具体地说，辅酶A水平必须增加，线粒体才能有效地进行脂肪酸p-氧化，PanK2感知线粒体p-氧化的状态，并相应地调整辅酶A的生物合成速率。最后一个授权期的结果揭示了PanK2活性的新的调控生化机制，我们将研究PanK2活性复杂控制的机制基础，并确定致病的PanK2突变是否在这一特性中发生变化。我们还将讨论PanK2在调节细胞对从葡萄糖到脂肪酸的代谢转变的反应中所起的作用。这些结果将提供关于调控哺乳动物能量代谢的控制系统的基本信息，并为未来发展关于人类PKAN疾病的代谢基础的假说奠定科学基础。这项研究需要CoA生物合成、脂类代谢和蛋白质生物化学领域的专业知识，这些都是为解决这一问题而组建的调查小组的明显优势。

DESCRIPTION (provided by applicant): Coenzyme A (CoA) is the major acyl group carrier in biology and an essential cofactor in intermediary metabolism. Free CoA (unacylated) and its thioesters are allosteric ligands that govern the carbon flux through key metabolic enzymes and, in turn, control energy generation. There is ample evidence that intracellular CoA levels fluctuate in response to hormones, diet, and drugs, and are dysregulated in metabolic disorders such as diabetes. CoA is produced by a universal series of reactions starting from the vitamin pantothenate, and the flux through this pathway is controlled by the first enzyme, pantothenate kinase (PanK). Mammals have multiple PanK enzymes, each with unique regulatory properties, expression patterns and intracellular distributions. The critical importance of PanK in metabolism has been extensively validated in prokaryotic systems but there are significant gaps in our understanding of the biochemical regulation and role of the multiple mammalian PanK enzymes in the physiological control of metabolism. The importance of these enzymes was brought into sharp focus in mammalian systems by the discovery of the association of mutations in the human PANK2 gene with a progressive neurological disorder called PKAN. The human PanK2 isozyme is associated with mitochondria. The initial idea was that all disease- causing mutations inactivated PanK2 enzymatic function; however, our comprehensive analysis illustrates that a significant percentage of the mutations do not inactivate PanK2 suggesting that these missense mutations alter an important regulatory feature of the protein. We propose that mitochondrial PanK has a unique regulatory role in the metabolic adaptation of CoA levels to the utilization of fatty acids as a fuel source. Specifically, CoA levels must increase for mitochondria to efficiently carry out fatty acid p-oxidation, and PanK2 senses the status of mitochondrial p-oxidation and adjusts the rate of CoA biosynthesis accordingly. The results from the last grant period reveal the novel regulatory biochemical mechanism for PanK2 activity and we will investigate the mechanistic basis for the complex control of PanK2 activity and determine if the disease-causing PanK2 mutations are altered in this property. We will also address the role of PanK2 in regulating the cellular response to metabolic shift from glucose to fatty acids in cells. These results will provide essential information about the control systems that regulate energy metabolism in mammals and establish the scientific foundation for future development of hypotheses regarding the metabolic basis for the human PKAN disease. The research requires expertise in the areas of CoA biosynthesis, lipid metabolism and protein biochemistry which are the clear strengths of the investigative team assembled to pursue this problem.