Lipopolysaccharides (LPS), also known as endotoxins, are large molecules consisting of a lipid and a polysaccharide composed of O-antigen, outer core and inner core joined by a covalent bond; they are found in the outer membrane of Gram-negative bacteria. The term lipooligosaccharide ("LOS") is used to refer to a low-molecular-weight form of bacterial lipopolysaccharides.
Today, the term endotoxin is mostly used synonymously with LPS,[1] although there are a few endotoxins that are not related to LPS, such as the so-called delta endotoxin proteins secreted by Bacillus thuringiensis.
The toxic activity of LPS was first discovered and termed endotoxin by Richard Friedrich Johannes Pfeiffer, who distinguished between exotoxins, which he classified as a toxin that is released by bacteria into the surrounding environment, and endotoxins, which he considered to be a toxin kept "within" the bacterial cell and released only after destruction of the bacterial cell wall.[2]:84 Subsequent work showed that release of LPS from gram negativemicrobes does not necessarily require the destruction of the bacterial cell wall, but rather, LPS is secreted as part of the normal physiological activity of membrane vesicle trafficking in the form of bacterial outer membrane vesicles (OMVs), which may also contain other virulence factors and proteins.[3][4]
LPS is the major component of the outer membrane of Gram-negative bacteria, contributing greatly to the structural integrity of the bacteria, and protecting the membrane from certain kinds of chemical attack. LPS is the most abundant antigen on the cell surface of most Gram-negative bacteria, contributing up to 80% of the outer membrane of E. coli and Salmonella.[4] LPS increases the negative charge of the cell membrane and helps stabilize the overall membrane structure. It is of crucial importance to many Gram-negative bacteria, which die if it is mutated or removed; however, it appears that LPS is nonessential in at least some Gram-negative bacteria, such as Neisseria meningitidis, Moraxella catarrhalis, and Acinetobacter baumannii.[5]LPS induces a strong response from normal animal immune systems. It has also been implicated in non-pathogenic aspects of bacterial ecology, including surface adhesion, bacteriophage sensitivity, and interactions with predators such as amoebae.
LPS is required for the proper conformation of omptin activity; however, smooth LPS will sterically hinder omptins.
https://en.wikipedia.org/wiki/Lipopolysaccharide
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