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. 2019 Mar 6;11(3):226. doi: 10.3390/v11030226

Figure 1.

Figure 1

Biosynthesis pathway of histo-blood group antigens (HBGAs) by stepwise addition of monosaccharides to precursor structures. The FUT2 (secretor) gene encodes an α1,2-fucosyltransferase which adds a fucose residue in α1,2 linkage to the terminal galactose of the H type 1 precursor. Non-secretors, having a non-functional FUT2 enzyme, cannot synthesize the H type 1 antigen from its precursor and lack α1,2-linked fucose HBGAs in the intestinal mucosa and other secretions. The synthesis of the A and B antigens by the corresponding enzymes requires the presence of the H type 1 antigen, adding an N-acetylgalactosamine (A) or a galactose (B) in a α1,4 linkage on the galactose residue of the H type 1 antigen. The Lewis antigens are synthesized with the FUT3 enzyme which adds a α1,4-linked fucose residue on the N-acetylglucosamine of the H antigen or the H antigen precursor, generating Lewis a or Lewis b antigens respectively. Abbreviations: Gal: galactose; GlcNAc: N-acetylglucosamine; Fuc: fucose.