2. Nontemplet synthesis of glycosylation in the ER and gC The immediate precursors, used in glycosylation, are nucleotide sugars with a high energy ester bond (AG of its hydrolysis -5. kcal/mol), such aS CMP-salic acid GDP-manose, UDP-GICNAc. They are synthesized in the cytosol and can be actively transported actively by different antiports into the Er and GC. They are the donors of oligosaccharides, and the transfer a specific monosaccharide from an appropriate sugar donor to an appropriate sugar receptor, a growing oligosaccharide chain is catalyzed by group of membrane-bound enzyme called glycosyltransferases. Complex carbohydrates require a different enzyme at each step. The sequence of sugars that is assembled into an oligosaccharide depends on both the glycosyltransferases present in differet cells in a particular sequence and the accessibility of the oligosaccharide to the enzymes that participate in its construction. It is a nontemplet
2. Nontemplet synthesis of glycosylation in the ER and GC The immediate precursors, used in glycosylation, are nucleotide sugars with a high energy ester bond (G o’of its hydrolysis ~ -5 kcal/mol), such as CMP-salic acid, GDP-manose, UDP-GlcNAc. They are synthesized in the cytotsol and can be actively transported actively by different antiports into the ER and GC. They are the donors of oligosaccharides, and the transfer a specific monosaccharide from an appropriate sugar donor to an appropriate sugar receptor, a growing oligosaccharide chain is catalyzied by a group of membrane-bound enzyme called glycosyltransferases. Complex carbohydrates require a different enzyme at each step. The sequence of sugars that is assembled into an oligosaccharide depends on both the glycosyltransferases present in differet cells in a particular sequence and the accessibility of the oligosaccharide to the enzymes that participate in its construction. It is a nontemplet synthesis
P716 Dolichol CH3C-CHCH2+CH2C-CHCH2tCHz CH 1518 by tunicamycin UDP- UDP P UDP 5 GDP Dolichol phosphate N-Acetylglucosamine "flip Mannes ER lumen 3UDP→ 3 UDP
3 UDP 3 UDP Nascent Ribosome 4过 emorane 6 12 P Cytos 书 5 GDP 5 GDP-V 1 UMP Dolichol O= Glucose V:Mannose O=NAcetylglucosamine(NAG) MP= Dolichol phosphate
ambane (b) Step-by-step UDP-GlNAC glucose a mannose N-acetylglucosamine ⊙③③ CYTOSOL 4 Dclichol-p ER LUMEN growing polypeptide chain ⊙ cl Transfer to protein oligosaccharide protein transferase pid-linked oligosaccharide Aeparag ne n prate Figure 12-7 Assembly of Core Oligosaccharide tn asparagine during core ghcasyiation, (b)Step-by phospholipid translocator(Flippase). (c) Transfar of the completed core charice from dolichol phosphate to an asparagine of N-adetylglucosam ne NI, mannose MI and glucose
P360 Gytosol Fany acid sile chains COO Ethanolamine NH-CH,-CH- CH :CHa CH, oligosaccharide NH O TR I