Lipopolysaccharide (LPS) molecules are located in the outer leaflet of the outer membrane of bacteria such as Shigella flexneri and Salmonella enterica Typhimurium. LPS molecules are amphipathic and have three regions: lipid A, core sugars, and O antigen polysaccharides. The O antigen polysaccharides of S. flexneri and S. Typhimurium are composed of repeats of a tetrasaccharide unit, and range from 1 to >100 repeat units in length. The length of O antigen polysaccharides is regulated by the activity of Wzz proteins, with different Wzz proteins able to confer different modal length distributions. O antigen polysaccharide chain length impacts on virulence as it affects resistance to Complement, and actin based motility.
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