Metabolism of Aromatic Ring Precursors in Coenzyme Q Biosynthesis

科学价值：ATP，细胞的能量货币，主要由线粒体产生，线粒体是细胞内的膜结合体，将ATP的形成与碳水化合物或脂肪(脂肪)的受控燃烧联系在一起。辅酶Q(也称为泛醌或辅酶Q)是一种复杂的有机分子，对线粒体能量的产生至关重要。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。辅酶Q分子有两部分：(1)将其锚定在膜上的长尾；(2)芳环结构(苯二酚)，其性质使其能够输送形成ATP所必需的电子和质子。细胞通常被认为是从前体4-羟基苯甲酸(4-HB)合成苯醌环。虽然在酵母、植物和动物中已经鉴定出9个辅酶Q生物合成所必需的基因，但没有一个是合成4-Hb所必需的。因此，有关辅酶Q中芳香族苯醌成分的生成的主要问题仍然没有得到回答。4-Hb在细菌和酵母中被认为是通过苯丙烷生物合成途径中的香豆酸合成的，苯丙烷生物合成途径是植物用来产生各种代谢物的途径，或者在动物中是通过氨基酸酪氨酸合成的。最近的研究表明，酵母菌还可以利用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PABA是众所周知的叶酸的前体，叶酸是B族维生素之一，但以前从未与辅酶Q联系在一起。利用PABA作为环前驱体是生产辅酶Q的一条新的生物合成途径。这项研究利用酵母来定义PABA如何转化为辅酶Q，酪氨酸如何转化为4-Hb，以及香豆酸如何转化为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。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目标。广泛的影响：这个项目为本科生，特别是代表不足的少数族裔学生提供了进行尖端研究的机会。加州大学洛杉矶分校的本科生得出的结果表明，PABA是酵母中辅酶Q生物合成的环状前体。酵母缺失突变体的构建和鉴定，酵母生长的表征，辅酶Q含量的测定，在不同类型的微量培养基中培养的酵母的同位素标记，以及酵母脂提取物的制备和高效液相分析，都是由从事独立研究项目的本科生完成的。国际和平协会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，国际和平协会和联合国际都积极为妇女和代表不足的少数族裔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.