Molecular Mechanisms of Lipopolysaccharide Transport Driven by ABC Transporters

ABC转运蛋白驱动脂多糖转运的分子机制

• 批准号: 9923673
• 负责人: Maofu Liao
• 金额: $ 33.9万
• 依托单位: HARVARD MEDICAL SCHOOL
• 依托单位国家: 美国
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-08-01 至 2022-04-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9923673
• 关键词: ATP Hydrolysis; ATP-Binding Cassette Transporters; Amino Acids; Animals; Antibiotics; Architecture; Bacteria; Biochemical; Biogenesis; Carrier Proteins; Cell membrane; Charge; Complex; Cryoelectron Microscopy; Cytoplasm; Detergents; Development; Environment; Escherichia coli; GTP-Binding Protein alpha Subunits, Gs; Generations; Glycolipids; Gram-Negative Bacteria; Host Defense; Hydrophobicity; Innate Immune Response; Length; Ligation; Lipid A; Lipids; Lipopolysaccharide Biosynthesis Pathway; Lipopolysaccharides; Mediating; Membrane; Modeling; Molecular; Molecular Conformation; Names; Nucleotides; Nutrient; O Antigens; Oligosaccharides; Pathway interactions; Penetration; Permeability; Play; Poison; Polymers; Polysaccharides; Production; Proteins; Regulation; Resolution; Role; Series; Side; Structure; Techniques; Transmembrane Transport; conformational conversion; innovation; insight; nanodisc technology; nanodisk; novel; particle; pathogen; periplasm; protein complex; reconstitution; success; sugar

ABSTRACT Lipopolysaccharide (LPS) is present in the outer membrane of most Gram-negative bacteria, and plays a key role in constructing a proper cellular envelope for bacteria to survive in harsh environments. The tight packing of LPS in the outer membrane generates a network of charges and sugars, which selectively allow the entry of nutrient molecules, while limit the penetration of toxic compounds including detergents and antibiotics. Due to its critical importance in the biogenesis of bacterial membrane barrier, LPS biosynthesis and transport pathway is a particularly interesting target for developing novel antibiotics. LPS is also crucial in the host-pathogen interactions, and functions as a potent activator of innate immune response in the animals. LPS is a complex and highly variable glycolipid, composed of a lipid A moiety, a core oligosaccharide and a long-chain O-antigenic polysaccharide. The structure of lipid A and core oligosaccharide are relatively conserved, presumably due to their roles in maintaining the integrity of permeability barrier. In contrast, the O-antigen of LPS shows hypervariable structures, which is consistent with their functions in interacting with the outside environment and host defense. Gram-negative bacteria devote a large amount of energy and a sophisticated protein machinery to the efficient and proper production, transport and assembly of LPS molecules. The synthesis of LPS starts at the interface between the cytoplasm and the inner membrane, leading to the generation of lipid A-core oligosaccharide, also called rough LPS, which resides in the inner leaflet of the inner membrane. Rough LPS is flipped across the inner membrane by an ATP binding cassette (ABC) transporter, MsbA. The rough LPS in the periplasmic leaflet is further added with various lengths and forms of O-antigen, becoming a “smooth” LPS. For the LPS transport across the periplasm and to the outer membrane, seven proteins named as Lpt A-G are involved. Several lines of evidence converge to suggest a model, in which the Lpt proteins form a continuous bridge connecting the two membranes. The ABC transporter, formed as LptB2FG, is thought to extract the LPS molecules from the inner membrane, and transport them to the tightly associated bitopic LptC, and to the periplasmic LptA. Multiple LptA proteins may form a continuous bridge to reach the LptDE complex in the outer membrane, which mediates the LPS insertion into the outer leaflet of the outer membrane. Here we propose a series of structural and functional studies on the LPS transport protein machinery using a variety of biochemical and cryo-EM techniques. A molecular understanding on the function and regulation of the LPS transport pathway will contribute to the understanding of the biogenesis of the outer membrane of many Gram-negative bacteria, and also aid the development of novel antibiotics that directly target the bacterial membrane barrier.

抽象的 脂多糖（LPS）存在于大多数革兰氏阴性细菌的外膜中，发挥着重要作用。 在构建细菌在恶劣环境中生存的适当细胞膜方面发挥着关键作用。 LPS 在外膜中紧密堆积，产生电荷和糖网络，选择性地 允许营养分子进入，同时限制有毒化合物（包括清洁剂）的渗透 由于 LPS 在细菌膜屏障的生物发生中至关重要。 生物合成和转运途径是开发新型抗生素的一个特别有趣的目标。 LPS 在宿主与病原体的相互作用中也至关重要，并且是先天免疫的有效激活剂 LPS 是一种复杂且高度可变的糖脂，由脂质 A 部分组成， 核心寡糖和长链O-抗原多糖 脂质A和核心的结构。 寡糖相对保守，可能是由于它们在维持寡糖完整性方面的作用 相反，LPS 的 O 抗原显示出高变结构，这是一致的。 具有与外部环境相互作用和宿主防御的功能。 革兰氏阴性细菌投入大量能量和复杂的蛋白质机器来 LPS 分子的高效且正确的生产、运输和组装开始 LPS 的合成。 位于细胞质和内膜之间的界面，导致脂质 A 核心的产生 寡糖，也称为粗脂多糖，存在于粗内膜的内小叶中。 LPS 通过 ATP 结合盒 (ABC) 转运蛋白 MsbA 翻转穿过内膜。 周质小叶中的粗LPS进一步添加了各种长度和形式的O-抗原， 成为“平滑”的 LPS 对于 LPS 穿过周质并到达外膜的运输，七个。 一些名为 Lpt A-G 的蛋白质参与其中，多项证据共同提出了一个模型，其中 Lpt 蛋白形成连接两个膜的连续桥，形成 ABC 转运蛋白。 LptB2FG 被认为可以从内膜中提取 LPS 分子，并将它们转运到 紧密相关的双位LptC和周质LptA蛋白可形成连续的。 桥到达外膜中的 LptDE 复合物，介导 LPS 插入 在这里，我们提出了一系列关于外膜的结构和功能的研究。 LPS 使用多种生化和冷冻电镜分子技术运输蛋白质。 对 LPS 转运途径的功能和调节的了解将有助于 了解许多革兰氏阴性细菌外膜的生物发生，也有助于 直接针对细菌膜屏障的新型抗生素的开发。