protein O-linked glycosylation protein O-linked glycosylation via N-acetylgalactosamine https://github.com/geneontology/go-ontology/issues/27105 https://github.com/geneontology/go-ontology/issues/27107 https://github.com/geneontology/go-ontology/issues/30362 https://github.com/geneontology/go-ontology/issues/30366 https://github.com/geneontology/go-ontology/issues/30592 https://github.com/geneontology/go-ontology/issues/32044 Reactome:R-HSA-913709 mucin-type O-glycan synthesis GO:0016266 MetaCyc:PWY-7435 MetaCyc:PWY-7433 O-glycan processing A glycoprotein biosynthetic process starting with the covalent linkage of an N-acetyl-galactosamine via an alpha-glycosidic bond to the oxygen atom of a serine or threonine side chain in a protein, which can be further elongated with the sequential addition of sugar units resulting in the formation of a protein O-linked glycan. protein O-linked glycosylation via N-acetyl-galactosamine core O-glycan biosynthetic process protein O-linked GalNAcylation biological_process