Lipopolysaccharide

Lipopolysaccharide (LPS) is a molecule in the outer membrane of most Gram-negative bacteria, built from lipid and polysaccharide regions. Its lipid portion can trigger strong inflammatory immune responses.

Lipid A: The membrane-anchoring portion of LPS, consisting of a phosphorylated glucosamine disaccharide with attached fatty acids. This region anchors LPS and drives much of its inflammatory activity.
LPS biosynthesis: The cellular pathways that assemble lipopolysaccharide and transport it to the outer membrane of Gram-negative bacteria. These pathways determine how LPS is built and displayed on the cell surface.
Limulus amebocyte lysate test: A laboratory assay that detects bacterial endotoxin through clotting reactions in horseshoe crab blood-cell extracts. The assay is used to detect LPS contamination in injectable drugs and medical products.
Lipooligosaccharide: A bacterial outer-membrane glycolipid resembling LPS but lacking its long repeating O-antigen chain. It shares LPS's basic membrane role but has a shorter carbohydrate structure.
Core oligosaccharide: The short, conserved carbohydrate region linking lipid A to the O antigen in many LPS molecules. It connects the membrane anchor to the variable outer chain.
Lpt pathway: A protein transport system that moves lipopolysaccharide from the inner membrane to the outer membrane. It delivers newly made LPS to the surface where it forms the outer leaflet.
Recombinant factor C assay: An endotoxin test using recombinant horseshoe crab factor C, which is activated by bacterial LPS. It provides an alternative to animal-derived lysate assays for measuring endotoxin.
Peptidoglycan: A mesh-like polymer of sugars and peptides that gives bacterial cell walls structural strength. Unlike LPS, it forms the cell wall layer beneath the outer membrane.
O antigen: The variable, repeating polysaccharide chain extending from the core of many bacterial LPS molecules. Its variation creates distinctive bacterial surface types and affects immune recognition.
Toll-like receptor 4: An innate immune receptor that detects LPS with the accessory proteins MD-2 and CD14. Its recognition of LPS initiates a major pathway of antibacterial inflammation.

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