Figure 2. Structures and synthetic pathway for Lewis antigens in H. pylori.

FutA and FutB can fucosylate Type 2 chains that are present in the elongating LPS molecule via an α1,3-FucT activity, creating the Le^x antigen. Repetitive copies of such Le^x units are usually present in the O-antigen chain of H. pylori. FutC that possesses an α1,2-FucT activity may subsequently add a second fucose to the Le^x structure, generating the Le^y antigen. This process will cap the O-antigen chain and block further elongation of the LPS molecule and, consequently, Le^y can only be found at the terminal position of the O-antigen chain. Type 1 chains are structurally similar to the Type 2 chains and only differ in that they possess a β1,3-linkage instead of a β1,4-linkage between the Gal and GlcNAc saccharides in the precursor unit. In this case, fucosylation by FutA and FutB will require an α1,4-FucT activity and create a Le^a antigen, prior to α1,2-fucosylation by FutC that produces a di-fucosylated Le^b antigen. Gal = galactose, GlcNAc = N-Acetylglucosamine, Fuc = fucose.