Figure 7. Schematic representation of the biosynthesis of Neo-lactoseries and terminal glycosylation.

The β3GnT5 is essential for the synthesis of type 2 chains on glycolipids. The glycan chain it generates, GlcNAc-LacCer, is a substrate for a β4Gal-T that forms the type 2 chain, which may be further substituted by sialyltransferases and fucosyltransferases completing the biosynthesis of various Lewis antigens, including the sialyl-Le^x antigen. The action of other glycosyltransferases may also lead to termination of the chain with the formation of histo-blood groups H, A, and B. Alternatively, the type 2 chain may also be extended by the action of iGnT, leading to the biosynthesis polylactosamines, formation of polymeric Lewis antigens, and termination of the chain.