Novel roles for lipopolysaccharide modifications in immune evasion

革兰氏阴性菌的外膜形成一种渗透屏障，阻止抗菌素从 有效地到达驻留在细菌细胞壁或细菌胞浆内的分子靶标。 这种屏障功能依赖于外膜的中心构件之一--内毒素 (LP)。内毒素分子通过其脂类A部分锚定在细菌外膜上。脂蛋白A，An 酰化二糖，由人类免疫系统的模式识别受体TLR4感知。至 避免TLR4感应，细菌进化出修改其脂质A结构的机制，例如通过改变 其脂肪酸侧链的数量或长度，或添加或移除末端磷酸部分。 然而，并不是所有的内毒素修饰对TLR4的避免和许多内毒素的生物学功能都是重要的 修改只是一个很差的描述。 这项提议将检验新的假设，即特定的类脂A修饰使细菌能够逃脱 人鸟苷结合蛋白1(GBP1)对宿主免疫的影响我们最近证明了GBP1是一种 额外的真正的内毒素结合蛋白。细胞内的GBP1至少执行两项功能：i)它加速 内毒素介导的炎性小体激活的动力学和II)它直接结合到胞浆G-G表面。 负性细菌，在那里它作为表面活性物质与需要 穿透细菌外膜。在Aim1中，我们将识别特定的脂蛋白A修饰，这些修饰可以阻止 GBP1与人类两种重要病原体--细胞内肠道病原体表面的结合 鼠伤寒沙门氏菌和胞外致病菌铜绿假单胞菌。 GBP1存在于宿主细胞胞浆中，但GBP1也分泌到细胞外环境中。分泌型GBP1 在细菌性脑膜炎患者的血浆和脑脊液中可发现高浓度的。 然而，分泌的GBP1的生物学功能尚不清楚。因为我们发现GBP1与 胞外致病菌铜绿假单胞菌，我们将检测分泌的GBP1是否以及如何 在AIM2中对胞外细菌进行宿主防御。具体地说，我们将测试这个假设 GBP1与胞外抗菌肽具有协同作用。从概念上讲，AIM2还将 确定与GBP1协同作用的现有抗生素。目标1和目标2共同提供了路线图 许多革兰氏阴性菌感染治疗的新策略：靶向脂多糖修饰 参与GBP1逃逸的酶与抗生素的使用协同作用 GBP1。

The outer membrane of Gram-negative bacteria forms a permeability barrier blocking antimicrobials from efficiently reaching their molecular targets residing within the bacterial cell wall or inside the bacterial cytosol. This barrier function is dependent on one of the outer membrane’s central building blocks, lipopolysaccharide (LPS). The LPS molecule is anchored in the outer bacterial membrane by its lipid A moiety. Lipid A, an acylated disaccharide, is sensed by the pattern recognition receptor TLR4 of the human immune system. To avoid TLR4 sensing, bacteria evolved mechanisms to modify their lipid A structure, for example by changing the number or lengths of its fatty acid side chains, or adding or removing terminal phosphate moieties. However, not all LPS modifications are important for TLR4 avoidance and the biological function of many LPS modifications is only poorly characterized. This proposal will test the novel hypothesis that specific lipid A modifications enable bacteria to escape from host immunity exerted by human guanylate binding protein 1 (GBP1). We recently showed that GBP1 is an additional bona fide LPS-binding protein. Intracellular GBP1 executes at least two functions: i) it accelerates the kinetics of LPS-mediated inflammasome activation and ii) it binds directly to the surface of cytosolic Gram- negative bacteria, where it acts as a surfactant operating synergistically with antimicrobials that need to penetrate the bacterial outer membrane. In Aim1 we will identify specific lipid A modifications that block the binding of GBP1 to the surface of two important human pathogens: the intracellular enteric pathogen Salmonella enterica Typhimurium and the extracellular pathogen Pseudomonas aeruginosa. GBP1 resides in the host cell cytosol but GBP1 is also secreted into the extracellular milieu. Secreted GBP1 can be found at high concentrations in plasma and cerebrospinal fluids of bacterial meningitis patients. However, the biological function of secreted GBP1 is unknown. Because we found that GBP1 binds to the extracellular bacterial pathogen Pseudomonas aeruginosa, we will test whether and how secreted GBP1 can exert host defense to extracellular bacteria in Aim2. Specifically, we will test the hypothesis that secreted GBP1 works synergistically with extracellular antimicrobial peptides. Conceptually related, Aim2 will also identify extant antibiotics that operate synergistically with GBP1. Together, Aims 1 and 2 provide a roadmap towards novel strategies for the treatment of many Gram-negative infections: targeting LPS-modifying enzymes involved in GBP1 evasion combined with the use of antibiotics that operate synergistically with GBP1.