BIOSYNTHESIS OF MEMBRANE GLYCOLIPIDS IN RHIZOBIUM

根瘤菌膜糖脂的生物合成

基本信息

批准号：
6519607
负责人：
Christian R Raetz
金额：
$ 29.67万
依托单位：
DUKE UNIVERSITY
依托单位国家：
美国
项目类别：
财政年份：
1995
资助国家：
美国
起止时间：
1995-07-01 至 2004-06-30
项目状态：
已结题

项目摘要

Lipopolysaccharides (LPSs) are remarkable glycolipids that comprise the outer surfaces of Gram-negative bacteria, including the symbiotic organism, Rhizobium leguminosarum. In Escherichia coli, the lipid A anchor of LPS is a hexa-acylated disaccharide of glucosamine, bearing phosphate moieties at positions 1 and 4'. The minimal LPS required for a growth of E.coli consists of lipid A and two extra sugars. Emerging genomic sequences indicate that the enzymes that make lipid A in E. coli are present in most other Gram-negative bacteria. Lipid A (often termed endotoxin) is also the active component of LPS responsible for the clinical complications of Gram-negative sepsis. Minor modifications in the structure of lipid A can have profound effects on pathogenesis. Some lipid A analogs are actually potent endotoxin antagonists. Compared to E. coli, the chemical structures of the lipid A and core domains of R. leguminosarum LPS are very unusual. R. leguminosarum lipid A lacks the and 4'phosphates, but is modified with galacturonic acid at position 4'. It is acylated with a peculiar 28 carbon fatty acid, and contains 2-deoxy-2-aminogluconate in place of the proximal glucosamine. The structure of R. leguminosarum LPS indicates the existence of novel enzymes for generating diverse lipid A and core species. It is now established that the first seven enzymes of lipid A biosynthesis are in fact the same in E. coli and R. leguminosarum. The differences arise in the later stages of the pathway. To date, enzymes identified as unique to R. leguminosarum include a 4'-phosphatase that is also a phosphotransferase, a 1-phosphatase, a long chain acyltransferase with its own acyl carrier protein, and three distinct core glycosyltransferases. Characterization of the R. leguminosarum system should provide insights into the function of lipid A-like molecules, including special roles during symbiosis in plants, and affords the opportunity to create novel lipid A hybrids that may have interesting adjuvant or antagonist activities. Some structural features of R. leguminosarum lipid A are seen in human pathogens. Legionella pneumophila lipid A contains a C28 chain, while Porphyromonas gingivalis and Helicobacter pylori lipid A lack the 4' phosphate. In the coming grant period, the specific aims are: I) cloning of the C28 acyltransferase of R. leguminosarum; II) analysis of the lipid A 4'-phosphatase/phosphotransferase, especially its ability to synthesize PtdIns-4-P; III) determination of the enzymatic basis for proximal unit diversity in R. leguminosarum lipid A; and IV) characterization of enzymes that incorporate the unique inner core sugars of R. leguminosarum LPS.

脂多糖（LPSS）是杰出的糖脂，包括革兰氏阴性细菌的外表面，包括共生生物，根瘤菌。在大肠杆菌中，LPID A的锚固型是葡萄糖胺的Hexa酰化二糖，在1和4'位置含有磷酸盐部分。大肠杆菌生长所需的最小LP由脂质A和两种额外的糖组成。新兴的基因组序列表明，大多数其他革兰氏阴性细菌中都存在使大肠杆菌中脂质A的酶。脂质A（通常称为内毒素）也是负责革兰氏阴性败血症临床并发症的LP的活性成分。脂质A结构的微小修饰会对发病机理产生深远的影响。某些脂质A类似物实际上是有效的内毒素拮抗剂。与大肠杆菌相比，脂质A的化学结构和豆科氏菌LPS的核心结构域非常不寻常。 R.豆类脂质A缺少和4磷酸盐，但在4'位置用半乳酸酸修饰。它用特殊的28碳脂肪酸酰化，并含有2-脱氧-2-氨基氨基葡萄糖酸酯代替近端葡萄糖胺。豆科氏菌LPS的结构表明存在用于产生多种脂质A和核心物种的新型酶。现在已经确定，脂质A生物合成的前七种酶实际上在大肠杆菌和豆科氏菌中相同。这些差异在路径的后期阶段出现。迄今为止，豆科氏菌独有的酶包括一个4'-磷酸酶，它也是一种磷酸转移酶，一种1-磷酸酶，一种具有自己的酰基载体蛋白的长链酰基转移酶，以及三种不同的核心核心糖基糖基转移酶。豆科氏菌系统的表征应提供有关脂质A样分子功能的见解，包括植物中共生期间的特殊作用，并提供了创建新型脂质杂种的机会，这些混合体可能具有有趣的辅助或拮抗剂活性。豆科氏菌脂质A的一些结构特征在人类病原体中看到。肺炎军团脂质脂质A包含C28链，而卟啉单胞菌和幽门螺杆菌的幽门螺杆菌脂质A缺乏4'磷酸盐。在未来的赠款期间，具体目标是：i）豆科氏菌的C28酰基转移酶克隆； ii）分析脂质A 4'-磷酸酶/磷酸转移酶，尤其是其合成PTDINS-4-P的能力； iii）确定豆科氏菌脂质的近端单位多样性的酶基基础； iv）表征融合了豆科氏菌LPS的独特内核糖的酶。