Lipopolysaccharide O antigen size distribution is determined by a chain extension complex of variable stoichiometry inEscherichia coliO9a

Significance Lipopolysaccharides (LPSs) are unique glycolipids that are characteristic components of outer membranes in Gram negative bacteria and play important roles in pathogenesis. Many LPSs contain a long-chain polysaccharide (known as the O antigen) whose length can be an important factor in bacterial resistance to complement-mediated killing. While components involved in chain-length determination are known in many systems, the underlying regulatory mechanism is not. Here we apply a mathematical modeling approach that integrates the existing structural and biochemical data to develop a new model, variable geometry, for chain-length regulation using the prototype for O antigens whose synthesis involves the widespread ATP-binding cassette transporter-dependent pathway.