Regional differences in membrane composition across the Golgi stack O15um gure 8 19 Regional differences in membrane compo- the medial cisternae. (c)The enzyme nucleoside diphos sition across the Golgi stack. (a)Reduced osmium tetroxide phatase, which splits dinucleotides (e.g, UDP)after they preferentially impregnates the cis cisternae of the golgi complex.(b) The enzyme mannosidase Il, which is involved have donated their sugar, is preferentially localized in the trans cisternae. (a, c: From Robert S Decker, J. Cell Biol. 61:603 a)Cis cisternae of Golgi complex: reduced osmium tetroxide(OsO4) b)Reaction for enzyme mannosidase Il, localized in the medial Reaction fo
a) Cis cisternae of Golgi complex: reduced osmium tetroxide(OsO4 ); b) Reaction for enzyme mannosidase II , localized in the medial; c) Reaction for enzyme nucleoside diphosphatase , localized in the trans cisternae. ❖Regional differences in membrane composition across the Golgi stack
B The Functions of Golgi complex Biosynthesis of core oligosaccharide for N-linked glycosylation Glycosylation in ER Attachment of core oligosacchar to asparagine residues the e golgi complex CGN Attachment of N-acetylgalactosamine Golgi complex to serine or threonine First step of phosphorylation of plays a key role in lysosomal proteins the assembly of the Removal of mannose Second step of phosphorylatio carbohydrate of lysosomal proteins component of 6I Medial Removal of mannose glycoproteins and cisternae Attachment of N-acetylglucosamine glycolipids Addition of galactose Addition of sialic acid TGN o: Addition of sialic acid Attachment of sulfate to tyrosine
B. The Functions of Golgi complex ❖Glycosylation in the Golgi complex Golgi complex plays a key role in the assembly of the carbohydrate component of glycoproteins and glycolipids
glucosidase I 0 2 UDP Golg glucosidase ll mannosidase / -acetylglucosamine mannosidase Il transferase I CMP ER mannosidase UDP added here high-mannose Endo H- Endo H resistant conthe oligosaccharide sensltive oligosaccharide ER LUMEN GOLGI LUMEN KEY: O=N-acetylglucosamine (GlcNAc) O=mannose (Man)O=glucase(Glc O=galactose (Gall o- N-acetylneuraminic acid (sialic acid, or NANa e The core carbohydrate of N-linked oligosaccharides is sembled in the rer Modifications to N-linked oligosaccharides are completed in the Golgi complex. O-linked oligosaccharides takes place in Golgi complex
The core carbohydrate of N-linked oligosaccharides is assembled in the rER. Modifications to N-linked oligosaccharides are completed in the Golgi complex. O-linked oligosaccharides takes place in Golgi complex
Structure of typical O-and N-linked oligosaccharides a O-linked oligosaccharides (b) N-linked complex oligosaccharides Glo NAN NANA NANA B(1→2 忆2→ ax(2→3) B(1→4》 (1→ Amino Amino GIcNAc GIcNAc GlcNAC HyI-acid B(1 B(1→2 β(1→4) Collagen N Man x(1→6 Man NANA NANA Core region a(2→3 a{2→6) P(1→4 B(1→3) →Ga|NAc GICNAC (1→4 GNA←6←1)a Fuc Amino √Amin Ser-acid Afterr Kornfeld Glycophorin Amino Amino and S Kornfeld NANA= N- Acetylneuraminic acid (sialic acid) Gal= Galactose 1985. Annu. Rev GaINAc- N-Acetylgalactosamine Man e Mannose GlcNAC= N-Acetylglucosamine (conserved) Fuc= Fucose Biochem. 45: 631 GIcNAc= N-Acetylglucosamine UCOSe
Structure of typical O- and N-linked oligosaccharides Core Region After R. Kornfeld and S. Kornfeld, 1985, Annu. Rev. Biochem. 45:631
What is the purpose of glycosylation? linked glycosylation is prevalent in all eucaryotes. but is absent from procaryotes. >It dont require a template. There is an important difference between the construction of an oligosaccharide and the synthesis of DNA, RNA and protein >Important functions (1)One might suspect that they function to aid folding and the transport process; for example, carbohydrate as a marker during protein foldingin ER and the use of carbohydrate-binding lectins in guiding ER-to Golgi transport (2)Limit the approach of other macromolecules to the protein surface, more resistantto digestion by proteases. (3)Regulatory roles in signaling through the cell-surface recepto Notch, to allows these cells to respond selectively to activating stimuli
❖What is the purpose of glycosylation? N-linked glycosylation is prevalent in all eucaryotes, but is absent from procaryotes. ➢It don’t require a template. There is an important difference between the construction of an oligosaccharide and the synthesis of DNA,RNA,and protein. ➢Important functions: (1) One might suspect that they function to aid folding and the transport process; for example, carbohydrate as a marker during protein folding in ER and the use of carbohydrate-binding lectins in guiding ER-toGolgi transport. (2) Limit the approach of other macromolecules to the protein surface, more resistant to digestion by proteases. (3) Regulatory roles in signaling through the cell-surface receptor Notch, to allows these cells to respond selectively to activating stimuli