Identification of a Protein Complex That Assembles Lipopolysaccharide in the Outer Membrane of Escherichia coli

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 103; no. 31; pp. 11754 - 11759
• Main Authors: Wu, Tao, McCandlish, Andrew C., Gronenberg, Luisa S., Chung, Shu-Sin, Silhavy, Thomas J., Kahne, Daniel
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 01.08.2006; National Acad Sciences
• Subjects: Antibodies; Bacteria; Bacterial Outer Membrane Proteins - genetics; Bacterial Outer Membrane Proteins - metabolism; Biogeochemistry; Biological Sciences; Biological Transport - physiology; Cell growth; Cell Membrane - chemistry; Cell Membrane - metabolism; Cell Membrane - ultrastructure; Cell Survival; Cellular biology; Cellular immunity; Enzymes; Escherichia coli; Escherichia coli - metabolism; Escherichia coli - ultrastructure; Escherichia coli Proteins - genetics; Escherichia coli Proteins - metabolism; Lipids; Lipopolysaccharides - chemistry; Lipopolysaccharides - metabolism; Lipoproteins; Molecular biology; Multiprotein Complexes; Periplasm; Phospholipids; Plasmids; Protein synthesis; Proteins
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0604744103

The outer membrane of most Gram-negative bacteria is made up of LPS, and in nearly all bacteria that contain LPS it is essential for the life of the organism. The lipid portion of this molecule, lipid A, also known as endotoxin, is a potent activator of the innate immune response. More than 50 genes are required to synthesize LPS and assemble it at the cell surface. Enormous progress has been made in elucidating the structure and biosynthesis of LPS, but until recently the cellular components required for its transport from its site of synthesis in the inner membrane to its final cellular location at the cell surface remained elusive. Here we describe the identification of a protein complex that functions to assemble LPS at the surface of the cell. This complex contains two proteins: Imp, already identified as an essential outer-membrane protein implicated in LPS assembly; and another protein, RIpB, heretofore identified only as a rare lipoprotein. We show that RIpB is also essential for cell viability and that the Imp/RIpB complex is responsible for LPS reaching the outer surface of the outer membrane.