part of heparan sulfate proteoglycan biosynthetic process heparin proteoglycan biosynthetic process chondroitin sulfate proteoglycan biosynthetic process dermatan sulfate proteoglycan biosynthetic process glycosaminoglycan-protein linkage region biosynthetic process https://github.com/geneontology/go-ontology/issues/28977 https://github.com/geneontology/go-ontology/issues/29294 https://github.com/geneontology/go-ontology/issues/30378 MetaCyc:PWY-6557 Glycosaminoglycan biosynthesis, linkage tetrasaccharide 2024-11-27T13:13:42Z sjm glycosaminoglycan-protein linkage region biosynthesis GO:0120532 Reactome:R-HSA-1971475 biological_process The formation of a tetrasaccharide linker sequence (xylose-galactose-galactose-glucuronate) on specific serine residues of a core protein, on to which dermatan sulfate, chondroitin sulfate, heparan sulfate or heparin glycosaminoglycans may be assembled to synthesise the corresponding proteoglycan. protein O-linked glycosylation via xylose