1.5 The core oligosacchride structure ismodifed by glcyosidases andglycosyltransferase
1.5 The core oligosacchride structure is modified by glcyosidases and glycosyltransferase
Processing of N-linked glycanTrans-GolgiMedial GolgiExoglycosidasesCis-GolgiEndoplasmicreticulumERSialyl-Oligosaccharyl-GolgiGICNAC-GolgiGIcNAc-Galactosyl-transferaseglucosidasesmannosidasestransferasemannosidasetransferasetransferasetransferasesIA.IB,IC11ITand llERmannosidaseMannoseGlcNAcGlucoseDolicholphosphateSialic AcidGalactoseProteinbackbone
Processing of N-linked glycan! Exoglycosidases!
Common complexN-linked glycansHigh-mannose oligosaccharideComplex:bi-antennaryNeuAco2-6GalB1-4GlcNAcB1-2Mana1Manβ1-4GlcNAcβ1-4GIcNAcβ1-AsnNeuAcα2-6GalB1-4GlcNAcβ1-2Manα1Complex:tri-antennaryNeuAcα2-6Galβ1-4GlcNAcβ1-2Manα1GICNAc-ManB1-4GlcNAcβ1-4GlcNAcβ1-AsntransferaseIVNeuAcα2-6Galβ1-4GlcNAcB1ManaNeuAco2-6GalB1-4GlcNAcB1GIcNAc-transferaseVNeuAcα2-6Galβ1-4GlcNAcB1Complex:tetra-antennaryManaNeuAc2-6GalB1-4GIlcNAcB1GIcNAc-Manβ1-4GIcNAcβ1-4GlcNAcβ1-AsntransferaseIvNeuAcα2-6GalB1-4GlcNAcβ1Mana1NeuAcα2-6GalB1-4GlcNAcB1
Common complex N-linked glycans! High-mannose oligosaccharide!
RareglycanscontainingfiveormorebranchesAddition of asingle Gal and Sialicacid residueto eachGIcNAcGalactosyltransferase sialyltransferaseLocate further along in the secretory pathwayInthetransportionoftheGolgiapparatus(高尔基体)and the trans-Golgi networkGalactose:β1-4linkageTerminal sialic acid: α2-3 or α2-6 linkageResultingN-acetylneuraminic acid-galactose (NeuAc-Gal)Cappingstructure
Rare glycans containing five or more branches! Addition of a single Gal and Sialic acid residue to each GlcNAc! Galactosyltransferase sialyltransferase! Locate further along in the secretory pathway! In the trans portion of the Golgi apparatus (高尔基体) and the trans-Golgi network! Galactose: β1-4 linkage! Terminal sialic acid: α2-3 or α2-6 linkage ! ! Resulting N-acetylneuraminic acid-galactose (NeuAc-Gal)! Capping structure! !
Donors ------ nucleotide sugarsUDP-GlcNAc,UDP-Galcytidine monophosphate (CMP)-NeuAcTopological issueAll rxns occur in the lumen of the Golgi apparatusyet the donors are made in the cytoplasmNo translocation intermediate analogous to dolicholphosphomannose usedin dolichol precursorbiosynthesisTransportors: faciliate entry of the donors into the luminalcompartmentAntiporters:GlcNAcUDP by-pdt to UMP
Donors - nucleotide sugars! UDP-GlcNAc, UDP-Gal, ! cytidine monophosphate (CMP)-NeuAc! Topological issue! All rxns occur in the lumen of the Golgi apparatus,! yet the donors are made in the cytoplasm! No translocation intermediate analogous to dolichol phosphomannose used in dolichol precursor biosynthesis! ! Transportors: faciliate entry of the donors into the luminal compartment! Antiporters ! : ! GlcNAc! UDP by-pdt to UMP ! !