Lipopolysaccharide is transported to the cell surface by a membrane-to-membrane protein bridge

• Published in: Science (American Association for the Advancement of Science) Vol. 359; no. 6377; pp. 798 - 801
• Main Authors: Sherman, David J., Xie, Ran, Taylor, Rebecca J., George, Alexander H., Okuda, Suguru, Foster, Peter J., Needleman, Daniel J., Kahne, Daniel
• Format: Journal Article
• Language: English
• Published: United States The American Association for the Advancement of Science 16.02.2018
• Subjects: Adenosine triphosphate; Antibiotics; ATP; Bacteria; Bacterial proteins; Biological Transport; Carrier Proteins - metabolism; Cell Membrane - chemistry; Cell Membrane - metabolism; Cell surface; Escherichia coli - metabolism; Escherichia coli Proteins - metabolism; Gram-negative bacteria; Lipopolysaccharides; Lipopolysaccharides - metabolism; Membrane proteins; Membranes; Outer membranes; Proteins; Transport processes
• ISSN: 0036-8075; 1095-9203; 1095-9203
• DOI: 10.1126/science.aar1886

The outer membrane of Gram-negative bacteria is composed of lipopolysaccharide, a large glycolipid that prevents drugs from entering the cells. Disrupting lipopolysaccharide assembly hypersensitizes bacteria to antibiotics. Sherman et al. used biochemical tools to observe lipopolysaccharide transport. Seven proteins, which are conserved in all Gram-negative bacteria, appear to form a protein bridge that uses adenosine triphosphate to power transport of lipopolysaccharide from one membrane to another. The ability to monitor intermembrane transport of lipopolysaccharide will help in efforts to develop and characterize inhibitors. Science , this issue p. 798 Reconstitution of lipopolysaccharide transport shows that a protein bridge mediates membrane-to-membrane transport using adenosine triphosphate. Gram-negative bacteria have an outer membrane that serves as a barrier to noxious agents in the environment. This protective function is dependent on lipopolysaccharide, a large glycolipid located in the outer leaflet of the outer membrane. Lipopolysaccharide is synthesized at the cytoplasmic membrane and must be transported to the cell surface. To understand this transport process, we reconstituted membrane-to-membrane movement of lipopolysaccharide by incorporating purified inner and outer membrane transport complexes into separate proteoliposomes. Transport involved stable association between the inner and outer membrane proteoliposomes. Our results support a model in which lipopolysaccharide molecules are pushed one after the other in a PEZ dispenser–like manner across a protein bridge that connects the inner and outer membranes.