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. Author manuscript; available in PMC: 2018 Feb 14.
Published in final edited form as: Adv Cancer Res. 2015 Feb 7;126:53–135. doi: 10.1016/bs.acr.2014.11.002

Figure 3.

Figure 3

The biosynthesis of O-GalNAc-type O-glycans is initiated and completed in the Golgi apparatus. The ppGalNAcT family of enzymes adds N-acetylgalactosamine from the nucleotide sugar donor UDP-GalNAc to proteins entering the Golgi to form the Tn antigen. The Tn antigen is normally a precursor to a wide variety of other structures, deriving from modifications of the GalNAc residue, to generate core 1, core 2, and core 3 O-glycans. The key reaction is the addition of galactose from UDP-Gal by the enzyme termed T-synthase, which generates the common core 1 O-glycan. The core 1 and/or core 2 O-glycans are found in all human cells. Such glycans are extended by various glycosyltransferases using specific nucleotide sugar donors, e.g., UDP-Gal, UDP-GlcNAc, UDP-GalNAc, GDP-Fuc, CMP-Sialic acid, etc.