LIPID A MODIFICATION SYSTEMS IN GRAM-NEGATIVE BACTERIA

脂多糖(LPS)是构成革兰氏阴性菌外表面的一种重要糖脂 细菌，包括共生生物豆根瘤菌。在大肠杆菌中，脂类A锚定 脂多糖是一种氨基葡萄糖的六酰化二糖，在1和4‘位含有磷酸基团。这个 大肠杆菌生长所需的最小内毒素由脂肪A和两个额外的糖组成。新兴基因组学 序列显示，在大多数其他革兰氏阴性菌中，产生脂肪A的酶在大肠杆菌中也存在 细菌。A类脂蛋白(通常称为内毒素)也是内毒素的活性成分，与临床上 革兰氏阴性脓毒症的并发症。对脂类A结构的微小修改可以产生深远的影响 对发病机制的影响。一些类脂A实际上是有效的内毒素拮抗剂。 与大肠杆菌相比，豆类脂多糖的脂蛋白A和核心区的化学结构是 非常不寻常。豆腐乳杆菌类脂A缺乏1‘和4’磷酸，但在 位置4‘。它被一种特殊的28碳脂肪酸酰化，并含有适当的2-脱氧-2-氨基葡萄糖酸 近端的氨基葡萄糖。豆类细菌脂多糖的结构表明存在新的酶 用于产生不同的类脂A和核心物种。现在已经确定，脂类A的前七种酶 I的生物合成在大肠杆菌和/？中实际上是相同的。豆科植物。这些差异出现在 路径。到目前为止，已鉴定为/？所特有的酶。豆类包括4‘-磷酸酶，该酶也是一种 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 独特的核心糖基转移酶。/？的表征。豆类系统应提供见解 研究类脂A分子的功能，包括在植物共生过程中的特殊作用，并提供 创造可能具有有趣的佐剂或拮抗活性的新的A类脂杂交物的机会。一些人 豆角菌类脂A的结构特征在人类病原体中可见。嗜肺军团菌脂A I含有C28链，而牙龈卟啉单胞菌和幽门螺杆菌类脂A缺乏4‘磷酸。 在即将到来的授权期内，具体目标是：1)克隆豆科牧草C28酰基转移酶； I ii)分析脂质A4‘-磷酸酶/磷酸转移酶，特别是其合成PtdIns-4-P的能力； Iii)近端单位多样性的酶基础的测定。豆类脂类A；和IV) 含有豆类脂多糖独特的核心糖类的酶的特性。

Lipopolysaccharides (LPSs) are remarkable glycolipids that comprise the outer surfaces of Gram-negative bacteria, including the symbiotic organism, Rhizobium leguminosamm. 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 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/?, leguminosarum LPS are very unusual. R. leguminosarum lipid A lacks the 1 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/?, 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 I biosynthesis are in fact the same in E. coli and /?. leguminosarum. The differences arise in the later stages of the pathway. To date, enzymes identified as unique to /?. 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 /?. leguminosarum system should provide insights into the functions 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/?, leguminosarum lipid A are seen in human pathogens. Legionella pneumophila lipid A i 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/?, leguminosarum; i 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 /?. leguminosarum lipid A; and IV) i characterization of enzymes that incorporate the unique inner core sugars of/?, leguminosarum LPS.