The biosynthesis of branched O-glycans.

The hypothesis put forward in this review is that the branching patterns at the core of Ser(Thr)-GalNAc oligosaccharides (O-glycans) determine the types of glycan that are synthesized and their functions. Biosynthetic pathways are presented for the four types of O-glycan core and for some of the more common glycans that are built on these cores. The four core types discussed are: (1) Gal beta 1-3GalNAc-alpha-Ser(Thr)-R, (2) Gal beta 1-3(GlcNAc beta 1-6)GalNAc-alpha-Ser(Thr)-R, (3) GlcNAc beta 1-3GalNAc-alpha-Ser(Thr)-R, and (4) GlcNAc beta 1-3(GlcNAc beta 1-6)GalNAc-alpha-Ser(Thr)-R. General rules concerning the control of synthesis of these molecules are derived.