Rhizobial Lipopolysaccharides Essential for Infection

描述（由申请人提供）：根瘤菌是革兰氏阴性土壤细菌 与豆科植物形成固氮共生体。一种特殊的根瘤菌 识别并感染特定的宿主植物。根瘤菌细胞表面 脂多糖（LPS）是重要的内吞入侵寄主根 根瘤细胞和分化成固氮类杆菌内的一个 宿主衍生的细胞内区室称为共生体。共生体 膜来源于宿主细胞的高尔基体和内质网 并且是酸性的并且氧气含量低。根瘤菌共生体类似于动物 在吞噬体衍生的细胞内存活的细菌病原体 感染，并引起慢性感染;例如布鲁氏菌。成员的LPS 具有非常长链的lip-A脂肪酸，27-OHC 28：0，（如 病原体为流产布鲁氏菌（Brucella abortus）。此外，从R. etli（Re）（一种豆类 共生体）和R.豆科植物vicae（Rlv）（豌豆共生体）具有 独特的脂质A和核心寡糖;例如，它们不含磷酸盐， 含有半乳糖醛酸。在共生过程中， O-链多糖（例如甲基化）和脂质-A。在Rlv的情况下， LPS和整个细菌变得疏水。的这种增加 疏水性主要是由于脂质-A 27-OHC 28：0部分的加倍。 提出LPS O-链修饰是粘附 细菌与宿主细胞膜结合，并且需要27-OHC 28：0部分 以在胞吞作用和共生体形成期间维持膜稳定性。的 该提案的目的是在结构上表征O链 修改，并确定Re和Rlv独特的功能 关于共生和LPS生物合成的结构特征。这 将通过Re和Rlv突变体的产生和分析来完成 在这些独特的结构特征（例如， 27-OHC 28：0掺入缺陷），并通过分离和 与特异性单克隆抗体结合的LPS片段的表征 其LPS表位在共生过程中发生变化。

DESCRIPTION (provided by applicant): Rhizobia are Gram-negative soil bacteria that form nitrogen-fixing symbioses with legumes. A specific rhizobial species recognizes and infects a specific host plant. Rhizobial cell surface lipopolysaccharides (LPSs) are important for endocytotic invasion of host root nodule cells and differentiation into nitrogen-fixing bacteroids within a host-derived intracellular compartment known as the symbiosome. The symbiosome membrane is derived from the Golgi and endoplasmic reticulum of the host cell and is both acidic and low in O2. Rhizobial symbionts are analogous to animal bacterial pathogens that survive in phagosome-derived intracellular compartments and cause chronic infections; e.g. Brucella. The LPSs from members of the Rhizobiaceae have a very long chain lipid-A fatty acid, 27-OHC28:0, (as does the pathogen, Brucella abortus). Also, LPSs from R. etli (Re) (a bean symbiont) and from R. leguminosarum bv. vicae (Rlv) (a pea symbiont) have unique lipid-A, and core oligosaccharide; e.g. they are devoid of phosphate and contain galacturonic acid. During symbiosis, modifications are made to the O-chain polysaccharide (e.g. methylation) and lipid-A. In the case of Rlv, both LPS and the entire bacterium become hydrophobic. This increase in hydrophobicity is due primarily to a doubling of the lipid-A 27-OHC28:0 moiety. It is proposed that the LPS O-chain modifications are required for adherence of the bacterium to the host membrane, and that the 27-OHC28:0 moiety is required to maintain membrane stability during endocytosis and symbiosome formation. The aims of this proposal are to structurally characterize the O-chain modifications, and to determine the functions of the Re and Rlv unique structural features with regard to both symbiosis and LPS biosynthesis. This will be accomplished through the creation and analysis of Re and Rlv mutants that are specifically altered in these unique structural features (e.g. defective in 27-OHC28:0 incorporation), and by the isolation and characterization of LPS fragments that bind to specific monoclonal antibodies whose LPS epitopes change during symbiosis.