Fig. 5From: Insights into the structure of Escherichia coli outer membrane as the target for engineering microbial cell factoriesThe model of the LPS and CA biosynthesis and transport pathway in E. coli K-12. a LPS biosynthesis and transport. Core-lipid A is upturned by the transmembrane protein MsbA on the inner membrane, the O-antigen unit is upturned and polymerized by Wzx and Wzy, respectively, forming O-antigen repeats, which are linked to the core-lipid A by WaaL to form the complete LPS, and then is transported into the OM by Lpt system. b CA biosynthesis and transport. The CA unit is synthesized in cytoplasmic, and assembled in membrane. Briefly, CA is the repeating polysaccharide unit assembled by various Glycosyltransferases (GT’s) at the C55-lipid linker by Wzx/Wzy dependent pathway, then is translocated toward the periplasm by Wzx flippase; and the polymerization for CA occurs via Wzy polymerase and the polysaccharide co-polymerase protein. The polymerized CA is secreted into the OM by WzaBack to article page