Figure 5. Schematic representation of the B₃ transferase structure and its interaction with galactose residues.

The schematic representation of the B glycosyltransferases is based on previous studies [3], [27]. The relative location of the ABO transferase for the cytoplasmic tail, transmembrane domain, stem region, calalytic domain and the galactose residues are shown. The exons 1 to 7 of the ABO gene encoding for the different parts of the B glycosyltransferases are indicated. The B glycosyltransferases catalyze the final step of B antigen synthesis by transferring 1,3-D-galactose residues onto H determinants as the specific acceptor glycoconjugates. As to B₃, the lack of exon 3 corresponding to the transmembrane and stem region of B glycosyltransferase likely produces B₃ protein that is unstable and causes a decrease in B₃ protein expression. It is also likely that, due to the short stem region, B₃ protein is less flexible and can not efficiently transfer 1,3-D-galactose to the H protein.