Figure 2.

Structures of different types of O-linked chains. (A) structure and biosynthesis of mucin-type O-linked chains. Four “core” structures are shown, which can be elongated by other sugars. (B) Addition of O-linked GlcNAc, mediated by O-GlcNAc transferase. Removal of the sugar is catalyzed by O-GlcNAc ase (not shown). (C) O-fucosylation. The O-linked fucose mounted on EGF repeats by POFUT1 can be elongated by β3GlcNAc through manic fringe (MFNG) and also by β4Gal and α6Sia (not shown). The O-linked fucose mounted on TSRs repeats by POFUT2 can be elongated by β3Glc (D) O-mannosylation. The structure shown is referred to as M3 and can be elongated by the repeated units of xylose and glucuronic acid.