(Xyl)1 (Ser)1 GAG core proteins Xylose is transferred to a serine residue on the core protein Authored: Jassal, B, 2011-10-31 EC Number: 2.4.2.26 Edited: Jassal, B, 2011-10-31 Pubmed11099377 Pubmed15294915 Pubmed15461586 Reactome Database ID Release 431878002 Reactome, http://www.reactome.org ReactomeREACT_120955 Reviewed: D'Eustachio, P, 2012-03-28 Xylosyltransferase 1 (XYLT1) catalyses the initial step in the tetrasaccharide linkage required for glycosaminoglycan biosynthesis. This reaction can take place in the Golgi apparatus and endoplasmic reticulum (not shown here). XYLT1 mediates the transfer of xylose from the active nucleotide sugar UDP-xylose to specific serine hydroxy groups in the core protein. A C-terminal DxD motif on the enzyme is thought to be critical for activity (Muller et al. 2005, Goetting et al. 2004). Xylosyltransferase 2 (XYLT2) belongs to the XYLT family, displaying 55% amino acid sequence homology to XYLT1, whose activity has yet to be demonstrated (Goetting et al. 2000).