PathwayStep1054 PathwayStep1053 PathwayStep1052 PathwayStep1051 A tetrasaccharide linker sequence is required for GAG synthesis Authored: Jassal, B, 2011-11-04 Edited: Jassal, B, 2011-11-04 GENE ONTOLOGYGO:0030203 Pubmed17239764 Pubmed4139221 Reactome Database ID Release 431971475 Reactome, http://www.reactome.org ReactomeREACT_121408 Reviewed: D'Eustachio, P, 2012-03-28 The biosynthesis of dermatan sulfate/chondroitin sulfate and heparin/heparan sulfate glycosaminoglycans (GAGs) starts with the formation of a tetrasaccharide linker sequence to the core protein. The first step is the addition of xylose to the hydroxy group of specific serine residues on the core protein. Subsequent additions of two galactoses and a glucuronide moiety completes the linker sequence. From here, the next hexosamine addition is critical as it determines which GAG is formed (Lamberg & Stoolmiller 1974, Pavao et al. 2006). Xylose is transferred to a serine residue on the core protein A second galactose is added in the tetrasaccharide linker A glucuronate moiety is the fourth addition to the tetrasaccharide linker Galactose is the second sugar added in the tetrasaccharide linker