Fig. 2

Complex N-linked oligosaccharides with variations in length, branching and sialylation of their LacNAc moieties. The scheme shows some steps of the biosynthesis of complex N-linked oligosaccharides highlighting the role of enzymes that generate variations of N-acetyllactosamine (LacNac) glycoconjugates, the preferred ligand of galectins. N-acetylglucosaminyltransferases (Mgat4 and 5) act sequentially in ramifications; galactosyltransferases (GalTs) catalyze the transfer of galactose to glycoprotein-bound N-acetylglucosamine forming LacNac of variable lengths; α2,6 sialyltransferase 1 (ST6Gal1) adds sialic acid in α2,6 linkages to terminal LacNac, preventing the binding of several galectins, except Gal-3 that also bind to internal LacNac; N-acetylglucosamine α2,3 sialyltransferase 1 (ST3Gal1) adds sialic acid to N-glycans in position α2,3, favoring the binding of Gal-8; fucosyltransferase-3 (Fut3) adds fucose to N-acetylglucosamine; Neuroaminidases (Neus) remove sialic acid affecting the binding of galectins