logging in or signing up Glycosylation Breezy Download Post to : URL : Related Presentations : Let's Connect Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Copy embed code: Embed: Flash iPad Dynamic Copy Does not support media & animations Automatically changes to Flash or non-Flash embed WordPress Embed Customize Embed URL: Copy Thumbnail: Copy The presentation is successfully added In Your Favorites. Views: 2839 Category: Education License: All Rights Reserved Like it (0) Dislike it (0) Added: June 15, 2007 This Presentation is Public Favorites: 1 Presentation Description No description available. Comments Posting comment... Premium member Presentation Transcript Slide1: Covalent Modification of protein termini and side chains: overview Slide2: Protein Topogenesis: Overview Slide3: . http://www.chem.qmul.ac.uk/iupac/misc/glycp.html A glycoprotein is a compound containing carbohydrate (or glycan) covalently linked to protein. The carbohydrate may be in the form of a monosaccharide, disaccharide(s). oligosaccharide(s), polysaccharide(s), or their derivatives (e.g. sulfo- or phospho-substituted). One, a few, or many carbohydrate units may be present. The most common modifications in glycoproteins occurs through N- or O- glycosidic bonds: The most common modifications in glycoproteins occurs through N- or O- glycosidic bonds O-linkage: Ser, Thr (GalNAc) N-linkage: Asn (GlcNAc) ~ 50% of all eukaryotic proteins are glycosylated. Of these, 90% contain N-linked glycans (motif Asn-X-Ser/Thr; X == P or D). The predominant sugars found in glycoproteins are glucose, galactose, mannose, fucose, GalNAc and GlcNAc. Slide5: Proteoglycans (modified by glycosaminoglycans) GPI-linked proteins N-linked glycoproteins. We are going to look at three types of carbohydrate modifications of proteins: Slide6: Proteoglycans An extreme form of protein glycosylation in which the carbohydrate units are polysaccharides that contain amino sugars (glycosaminoglycans). http://www.chem.qmul.ac.uk/iupac/misc/glycp.html The difference between proteoglycans and glycoproteins resides in the level and types of carbohydrate modifications (ie proteoglycans are andgt;andgt; complex) A proteoglycan is a protein glycosylated by one or more (up to about 100) glycosaminoglycans. The glycosaminoglycans are repeating disaccharide chains of three types: chondroitin sulfate/dermatan sulfate, heparan sulfate/heparin, or keratan sulfate. Glycosaminoglycans: Glycosaminoglycans Slide8: http://web.indstate.edu/thcme/mwking/glycans.html Also see table 19-4 from Alberts Glycosaminoglycans Slide9: Glycosaminglycans and proteoglycans can associate to form huge polymeric complexes in the ECM. Syndecan, an integral membrane proteoglycan Slide10: GPI anchors ('glypiation') Slide11: N-linked Glycosylation of Asn residues Helenius andamp; Aebi (2001) Science 291, 2364 N-linked glycoproteins all contain a common core carbohydrate consisting of 3 mannose groups and two GlcNAc groups. The precursor oligosaccharide is synthesized in a multi-step process and transferred to a protein en bloc: The precursor oligosaccharide is synthesized in a multi-step process and transferred to a protein en bloc Slide13: Helenius andamp; Aebi (2001) Science 291, 2364 Every N-linked glycan is subjected to extensive modification while traversing the Golgi by a battery of mannosidases, glycosyltransferases and glucosidases All of the diversity of N-linked oligosaccharide structures on mature glycoproteins results from later modifications of the original precursor. Modified N-linked glycans are divided into three families:: Modified N-linked glycans are divided into three families: Lots of heterogeneity amongst different proteins and even within a population of the same protein N-linked glycans play a role in at least three different stages during the existence of a glycoprotein:: N-linked glycans play a role in at least three different stages during the existence of a glycoprotein: Structure and function of mature glycoprotein (many examples) Intracellular transport and targeting eg, mannose-6 receptors for lysosomal transport Sorting of proteins in ER, Golgi and PM/secretion Protein folding and quality control in the ER Helenius and Aebi, Annu. Rev. Biochem, 2004, 73: 1019-1049 Slide16: Sears andamp; Wong (1998) Cell. Mol. Life Sci. 54, 223 Effects of glycosylation: • Rigidity Slide17: Effects of glycosylation: • Rigidity • Molecular recognition Saxon andamp; Bertozzi (2001) Ann. Rev. Cell. Dev. Biol. 17, 1 Slide18: Rudd et al. (2001) Science 291, 2370 ‘immunological synapse’ * Model * Antigen Presenting Cell T-Cell Orient binding faces Provide protease protection Restrict nonspecific lateral protein-protein interactions Structural rigidity Modulate geometry and spacing of interactions Slide19: Effects of glycosylation: • Rigidity Molecular recognition • Solution properties: Stokes radius, viscosity, solubility Secondary structure/nucleate b turns? Folding ◊ Rate ◊ Disulfide bond formation ◊ Proteolytic processing (This effect is highly variable: for some proteins glycosylation is essential, for others dispensable.) Stability • Activity • Serum half-life (asialoglycoprotein receptor) • Interaction with chaperones Slide20: 95% larger Rudd et al. (2001) Science 291, 2370 constrained to biantennary CHOs * Model * Structural roles for glycosylation in antibodies Glycosylation as a marker for protein quality control: Glycosylation as a marker for protein quality control ERAD: ER-associated degradation pathway COP: Coatomer protein ERGIC: ER-Golgi intermediate compartment TGN: Trans Golgi network Many mechanisms for protein folding and quality control are found in the ER Protein folding quality control (QC) occurs co-translationally in the lumen of the ER. N-linked glycosyl groups are utilized to help direct QC pathway Glycosylation as a marker for protein quality control: Glycosylation as a marker for protein quality control Calnexin and calreticulin are ER chaperones of the lectin superfamily, bind to terminal glc group Glucosyl transferase recognizes misfolded glycoprotein, adds terminal glucose group. You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.