The O antigen polysaccharide chain connects with the core region of lipid A at the periplasmic surface of the cell membrane to form a complete lipopolysaccharide molecule. The transfer of lipopolysaccharide molecules from the periplasmic space to the outer membrane, but the mechanism of its presentation in the outer membrane is still unclear. It is speculated that it may be achieved through the "Bayer bridge" at the attachment sites of the inner and outer membranes.

Waal (Rfal) is the only enzyme known to be related to the linker reaction. Waal can effectively connect large relative molecular weight polymers or small relative molecular weight oligomers to the core region of lipid A. The basic characteristic of the linking reaction is that it is conservative and does not depend on the O antigen synthesis pathway. The O antigen synthesized by different bacteria through different ways can be effectively connected and expressed on the cell surface, which is also the basis for the research and expression of heterologous O antigen of Escherichia coli K-12 genetic engineering strain.

The primary structure of Escherichia coli K-12 and Salmonella typhimurium Waal has no obvious similarity. Although both contain multiple transmembrane domains, their hydrophobic profiles are obviously similar, but their functions cannot be complimentary. The effective activity of each Waal enzyme may require the coordination of Waak (i.e. Rfak), indicating that the specific core structure modification or (and) the specific interaction between Waal and Waak protein may be required for the activity of each Waal enzyme. On the cell surface, O antigen can exist only in the way of binding with lipid A core (such as Salmonella typhimurium), or in the way of binding with or without lipid A core. The latter is represented by the O antigen of Vibrio cholerae O139. There is only a short (single repeating unit) oligosaccharide connected with the core, and the capsular polysaccharide with a large relative molecular weight (not connected with the core) contains the same repeating unit structure.