lipopolysaccharide biosynthesis UPa:UPA00030 LPS biosynthesis PMID:12045108 PMID:16953973 pathway Biosynthesis of lipopolysaccharide (LPS). LPS comprises three parts: i) polysaccharide (O) side chains (O-antigen); ii) core oligosaccharide; iii) lipid A. Lipid A contains unusual fatty acids (e.g. hydroxy-myristic acid) and is inserted into the outer membrane while the rest of the LPS projects from the surface. Core oligosaccharide contains unusual sugars (e.g. KDO, keto-deoxyoctulonate and heptulose). It contains two glucosamine sugar derivatives each containing three fatty acids with phosphate or pyrophosphate attached. The core polysaccharide is attached to lipid A, which is also in part responsible for the toxicity of gram-negative bacteria. The polysaccharide side chain is referred as the O-antigen of the bacteria. O side chain (O-antigen) is also a polysaccharide chain that extends from the core polysaccharide. LPS are major components of the cell wall of Gram-negative bacteria, contributing greatly to the structural integrity of the bacteria, and protecting the membrane from certain kinds of chemical attack. By increasing the negative charge of the cell wall LSP helps stabilize the overall membrane structure. LPS forms the amphipathic interface between Gram-negative bacteria and their environment and contributes protection against antibiotics and the complement system. The alternative name, endotoxin, is indicative of the capacity to cause septic shock by hyperstimulation of the immune system. PMID:11521077 endotoxin biosynthesis GO:0009103 bacterial outer membrane biogenesis lipopolysaccharide metabolism membrane lipid biosynthesis