PathwayStep1039 PathwayStep1037 PathwayStep1038 PathwayStep1035 PathwayStep1036 PathwayStep1041 PathwayStep1040 PathwayStep1034 Keratan sulfate biosynthesis Authored: Jassal, B, 2011-12-01 Edited: Jassal, B, 2011-12-01 GENE ONTOLOGYGO:0018146 Keratan sulfate (KSI) is the best characterised keratan sulfate. It is 10 times more abundant in cornea than cartilage. KSI is attached to an asparagine (Asn) residue on the core protein via an N-linked branched oligosaccharide (an N-glycan core structure used as a precursor in N-glycan biosynthesis). KSI is elongated by the alternate additions of galactose (Gal) and N-acetylglucosamine (GlcNAc), mediated by glycosyltransferases. Elongation is terminated by the addition of a single N acetylneuraminic acid (sialyl) residue. KSI is also sulfated on Gal and GlcNAc residues by at least two sulfotransferases (Funderburgh 2000, Funderburgh 2002, Quantock et al. 2010). KSI can be attached to asparagine residues on core proteins, creating so called proteoglycans (PGs). Seven common core proteins found in corneal and skeletal tissues are used as examples here. Pubmed11030741 Pubmed12512857 Pubmed20213925 Reactome Database ID Release 432022854 Reactome, http://www.reactome.org ReactomeREACT_121120 Reviewed: D'Eustachio, P, 2012-03-28 Further sulfation on galactose residues produces KSPG KSPG is secreted from the cell Sulfation of GlcNAc residues on Keratan-PG forms KSPG The keratan chain can be capped by N-acetylneuraminic acid B4GALTs add galactose to the N-glycan precursor B3GNT1,2,3,4,7 add GlcNAc to form Keratan-PG B4GALTs add another galactose to the chain B4GALTs can add galactose to a branch of keratan