Biochemistry and Structure of Lipid A Enzymes

 性状（由申请人提供）：脂质A是脂多糖的疏水膜锚，是一种基于葡糖胺的糖脂，构成革兰氏阴性菌外膜的外单层，保护细菌免受洗涤剂和抗生素的外部损伤。它也是脂多糖的活性成分，导致危及生命的革兰氏阴性脓毒性休克。脂质A由大肠杆菌Raetz途径的9种酶合成。杆菌脂质A生物合成的前六种酶是几乎所有革兰氏阴性菌生存所必需的，并且是新的抗生素靶标。在脂质A生成后，其从内膜的胞质表面翻转到周质表面，在周质表面处其可以通过对单个细菌物种特异性的脂质A修饰酶进一步转化。这些修饰有助于细菌逃避宿主免疫反应，适应环境变化，并产生改变的脂质A分子，显示出不同的生物活性。虽然已经进行了详细的结构分析的几个脂质A的生物合成和修饰酶，提供丰富的信息，结构辅助抑制剂的发展，其他人需要进一步的表征。该提案侧重于将UDP-二酰基葡糖胺（UDP-DAGn）转化为2，3-二酰基-GlcN-1-P（脂质X）的必需脂质A生物合成酶和脂质A修饰酶LpxE的生物化学和结构研究，LpxE对细菌毒力和单磷酸化脂质A（MPLA）（一种广泛使用的免疫抑制剂）的产生至关重要。这些研究有望对脂质A酶的结构和机制以及细菌外膜的生物发生和功能产生基本的见解，并最终有助于开发新的治疗方法以改善人类健康。

 DESCRIPTION (provided by applicant): Lipid A, the hydrophobic membrane anchor of lipopolysaccharide, is a glucosamine-based saccharolipid that constitutes the outer monolayer of the outer membrane of Gram-negative bacteria and protects bacteria from the external damage of detergents and antibiotics. It is also the active component of lipopolysaccharide that causes life-threatening Gram-negative septic shock. Lipid A is synthesized by nine enzymes of the Raetz pathway in E. coli. The first six enzymes of lipid A biosynthesis are required for the viability of virtually all Gram-negative bacteria and are novel antibiotic targets. After lipid A i generated, it is flipped from the cytosolic surface of the inner membrane to the periplasmic surface, where it can be further transformed by lipid A modification enzymes that are specific to individual bacterial species. These modifications help bacteria evade the host immune response, adapt to environmental changes, and generate altered lipid A molecules that display diverse bioactivities. Although detailed structural analyses of several lipid A biosynthetic and modification enzymes have been carried out, providing rich information for structure-aided inhibitor development, others require further characterization. This proposal focuses on biochemical and structural studies of the essential lipid A biosynthetic enzymes that convert UDP-diacylglucosamine (UDP-DAGn) to 2,3- diacyl-GlcN-1-P (lipid X) and the lipid A modification enzyme LpxE that is important for bacterial virulence and production of monophosphorylated lipid A (MPLA), a widely used immunotherapeutic agent. These studies are expected to generate fundamental insights into the structure and mechanism of lipid A enzymes as well as the biogenesis and function of the bacterial outer membrane, and ultimately contribute to the development of novel therapeutics to improve human health.