BIOSYNTHESIS OF MEMBRANE GLYCOLIPIDS IN RHIZOBIUM

脂多糖(LPS)是一种不同寻常的糖脂，组成外层 革兰氏阴性细菌外膜表面，包括菌株 根瘤菌。因为在工作中遇到的困难 这些物质，其疏水锚链的确切共价结构 脂蛋白(称为脂蛋白A)在1983年前是未知的。对这一概念的理解 脂类A的结构、生物合成和功能非常重要，因为 脂类A是脂多糖的活性成分，负责许多 革兰氏阴性败血症的临床并发症。因此，脂类A是 也称为内毒素。生物合成的研究进展 以及由P.I.发现的内毒素的分子生物学 单糖类A前体在体内积累的1983年 大肠杆菌磷脂酰甘油缺陷突变株。现在是时候了 确定类脂A对革兰氏阴性杆菌的生长是必不可少的 细菌和类脂A合成抑制剂可能是新的 抗生素。此外，脂类A的某些前体和类似物是 作为内毒素的类脂A的拮抗剂和可能的原型 寻找用于治疗内毒素诱导的新的药理药物 令人震惊。对其生物合成和药理性质的研究最多 内毒素是基于来自大肠杆菌的类脂A的结构， 明尼苏达州沙门氏菌和球形红杆菌。 这项拟议的工作旨在阐明类脂A的独特特征 豆科根瘤菌的生物合成。R的结构。 豆类脂肪A具有刺激性，因为它既缺乏1‘也缺乏4’。 在脂肪中常见的磷酸盐，在大肠杆菌中是至关重要的 脂类A的生物合成。豆腐病菌的类脂A也缺乏 氨基葡萄糖二糖的大肠杆菌脂A取而代之，它含有一种独特的 2-脱氧-2-氨基葡萄糖酸部分取代还原型氨基葡萄糖。 根瘤菌的类脂A也与长脂肪酸发生酰化反应，这种长脂肪酸在 大肠埃希菌。豆类根瘤菌中类脂A的结构表明 存在可用于制备的新酶 内毒素类似物。 尽管有其结构，豆腐杆菌类脂A仍可刺激合成 某些免疫细胞中的细胞因子，表明它具有一些 大肠杆菌脂类A.R.豆类脂类A的生物学特性及其生物学特性 前体需要进一步研究，以评估其可能的用途 内毒素模拟和/或拮抗剂。基因和基因的鉴定 产生豆类根霉特有的类脂A的酶也可能 为类脂A类分子在血管内皮细胞中的功能提供新的见解 革兰氏阴性细菌的外膜，因为它可能 创造新的类脂A结构，这种结构是大肠杆菌/根瘤菌的杂交种。 具体目标是：1)鉴定单糖和 豆腐病菌活细胞中的双糖脂A前体；2) 产生这种特殊结构物种的酶的鉴定 大豆根瘤菌中发现的类脂A的分离；3)精选根瘤菌的分离 脂类A合成缺陷的突变体；以及4)鉴定 内毒素激动剂根瘤菌的类脂A亚结构 和/或敌手。

Lipopolysaccharides (LPSs) are unusual glycolipids that make up the outer surface of the outer membranes of gram-negative bacteria, including strains of Rhizobium. Because of the difficulties encountered in working with these substances, the exact covalent structure of the hydrophobic anchor of LPS (termed lipid A) was unknown prior to 1983. An understanding of the structure, biosynthesis and function of lipid A is very important, because lipid A is the active components of LPS responsible for many of the clinical complications of gram-negative sepsis. For this reason lipid A is also known as endotoxin. Progress with the elucidation of the biosynthesis and molecular biology of endotoxins resulted from the P.I's. discovery in 1983 of monosaccharide lipid A precursors that accumulate in phosphatidylglycerol-deficient mutants of Escherichia coli. It is now established that lipid A is essential for the growth of gram-negative bacteria and that inhibitors of lipid A synthesis could be novel antibiotics. In addition, certain precursors and analogs of lipid A are antagonists of the action of lipid A as an endotoxin and may be prototypes for new pharmacological agents useful in the treatment of endotoxin-induced shock. Most studies of the biosynthesis and pharmacological properties of endotoxins have been based ont he structure of lipid A from E. coli, Salmonella minnesota and Rhodobacter sphaeroides. The proposed work seeks to elucidate the unique features of lipid A biosynthesis in Rhizobium leguminosarum. The structure of R. leguminosarum lipid A is provocative, as it lacks both the 1 and 4' phosphates that are commonly found in lipid As and are crucial in E. coli lipid A biosynthesis. Lipid A of R. leguminosarum also lacks the glucosamine disaccharide of E. coli lipid A. Instead, it contains a unique 2-deoxy-2-aminogluconate moiety in place of the reducing end glucosamine. Lipid A of Rhizobium is also acylated with long fatty acids not found in E. coli. The structure of lipid A in R. leguminosarum suggests the existence of novel enzymes that may be useful for the preparation of endotoxin analogs. Despite its structure, R. leguminosarum lipid A stimulates synthesis of cytokines in certain immune cells, showing that it has some of the biological properties of E. coli lipid A. R. leguminosarum lipid A and its precursors require further study to evaluate their possible utility as endotoxin mimics and/or antagonist. Identification of the genes and enzymes that generate the unique lipid A of R. leguminosarum may also provide new insights into the function of lipid A-like molecules in the outer membranes of gram-negative bacteria, since it may be possible to create novel lipid A structures that are E. coli/Rhizobium hybrids. The specific aims will be; 1) identification of monosaccharide and disaccharide lipid A precursors in living, cells of R. leguminosarum; 2) identification of the enzymes that generate the unusual structural species of lipid A found in R. leguminosarum; 3) isolation of selected Rhizobium mutants defective in lipid A synthesis; and 4) characterization of substructures of lipid A from strains of Rhizobium as endotoxin agonists and/or antagonists.