Metabolism of Aromatic Ring Precursors in Coenzyme Q Biosynthesis

科学价值：ATP是细胞的能量货币，主要在线粒体中产生，线粒体是细胞内的膜结合体，它将ATP的形成与碳水化合物或脂质（脂肪）的受控燃烧结合起来。辅酶Q（也称为泛醌或CoQ）是线粒体能量产生所必需的复杂有机分子。辅酶q也是一种重要的抗氧化剂，可以保护膜脂免受氧化损伤。CoQ分子由两部分组成：(1)一条长“尾巴”将其固定在膜上；(2)一个芳香环结构（苯醌），其特性使其能够运送ATP形成所必需的电子和质子。细胞通常被认为是由前体4-羟基苯甲酸（4-HB）合成苯醌环。虽然已经在酵母、植物和动物中发现了辅酶q生物合成所必需的9个基因，但没有一个是合成4-HB所必需的。因此，关于辅酶q的芳香族苯醌成分的生成，主要问题仍未得到解答。4-HB被认为是在细菌和酵母中通过苯丙酸生物合成途径合成的，苯丙酸是植物产生多种代谢物的途径，或在动物中通过氨基酸酪氨酸合成。最近的观察表明，酵母也可以使用4-氨基苯甲酸（pABA）作为辅酶q生物合成的环前体。这是令人惊讶的，因为众所周知，pABA是B族维生素之一叶酸的前体，但以前并没有与CoQ联系起来。利用pABA作为环前体代表了一种新的生产辅酶q的生物合成途径。本研究利用酵母确定pABA如何转化为CoQ，酪氨酸如何转化为4-HB，香豆酸如何转化为4-HB。因此，这项研究解决了活细胞中能量产生过程所需的基本生物化学问题。研究结果还可能导致在农业和医学上的应用，因为所涉及的酶是除草剂和抗菌剂的潜在靶标。更广泛的影响：该项目为本科生，特别是代表性不足的少数民族学生提供了进行前沿研究的机会。加州大学洛杉矶分校的本科生得出的结果表明，pABA是酵母中CoQ生物合成的环前体。酵母缺失突变体的构建和表征、酵母生长的表征、CoQ含量的测定、不同类型培养基培养酵母的同位素标记、酵母脂质提取物的制备和高效液相色谱分析等都是由本科生独立完成的研究项目。PI是加州大学洛杉矶分校化学和生物化学系多样性和领导委员会的主席，PI和Co-PI都积极为女性和代表性不足的少数民族本科生和研究生提供咨询和指导。

Scientific Merit:ATP, the cell's energy currency, is largely produced in mitochondria, membrane-bound bodies within cells that couple ATP formation to the controlled burn of carbohydrates or lipids (fat). Coenzyme Q (also known as ubiquinone or CoQ) is a complex organic molecule essential for mitochondrial energy production. CoQ is also a crucial antioxidant that can protect membrane lipids from oxidative damage. The CoQ molecule has two parts: (1) a long "tail" that anchors it in the membrane, and (2) an aromatic ring structure (benzoquinone) with properties that allow it to ferry electrons and protons essential to ATP formation. Cells are generally thought to synthesize the benzoquinone ring from the precursor 4-hydroxybenzoic acid (4-HB). Although nine genes essential for CoQ biosynthesis have been identified in yeast, plants and animals, none are required for 4-HB synthesis. Therefore, major questions remain unanswered regarding the generation of the aromatic benzoquinone component of CoQ. 4-HB has been believed to be synthesized in bacteria and yeast via coumarate from the phenylpropanoid biosynthesis pathway, a pathway used by plants to produce a wide variety of metabolites, or in animals by using the amino acid tyrosine. Recent observations indicate that yeast can also use 4-aminobenzoic acid (pABA) as a ring precursor in CoQ biosynthesis. This is surprising because pABA is a well-known precursor of folate, one of the B vitamins, but has not previously been connected with CoQ. The utilization of pABA as a ring precursor represents a novel biosynthetic pathway for the production of CoQ. This research utilizes yeast to define how pABA is converted to CoQ, how tyrosine is converted to 4-HB, and how coumarate is converted to 4-HB. This research, therefore, addresses the basic biochemistry required for energy generating processes in living cells. Results may also lead to applications in agriculture and medicine, as the enzymes involved are potential targets for both herbicides and antimicrobials.Broader Impacts:This project affords undergraduate students, particularly underrepresented minority students, the opportunity to do cutting edge research. UCLA undergraduate students generated the results identifying pABA as a ring precursor to CoQ biosynthesis in yeast. Construction and characterization of yeast deletion mutants, characterization of yeast growth, determination of CoQ content, isotopic labeling of yeast cultured in different types of minimal media, and preparation and HPLC analyses of yeast lipid extracts are all carried out by undergraduate students working on independent research projects. The PI is Chair of the Diversity and Leadership Committee in the UCLA Department of Chemistry and Biochemistry, and both the PI and Co-PI are active in advising and mentoring women and under-represented minority undergraduate and graduate students.