Glycoprotein - wikipedia Glycoprotein Not to be confused with peptidoglycan, proteoglycan, or glycopeptide. N - linked protein glycosylation ( N - glycosylation of N - glycans ) at Asn residues ( Asn - x-Ser / Thr motifs ) in glycoproteins. Glycoproteins are proteins which contain oligosaccharide chains ( glycans ) covalently attached to amino acid side - chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. Secreted extracellular proteins are often glycosylated. In proteins that have segments extending extracellularly, the extracellular segments are also often glycosylated. Glycoproteins are also often important integral membrane proteins, where they play a role in cell -- cell interactions. It is important to distinguish endoplasmic reticulum - based glycosylation of the secretory system from reversible cytosolic - nuclear glycosylation. Glycoproteins of the cytosol and nucleus can be modified through the reversible addition of a single GlcNAc residue that is considered reciprocal to phosphorylation and the functions of these are likely to be additional regulatory mechanism that controls phosphorylation - based signalling. In contrast, classical secretory glycosylation can be structurally essential. For example, inhibition of asparagine - linked, i.e. N - linked, glycosylation can prevent proper glycoprotein folding and full inhibition can be toxic to an individual cell. In contrast, perturbation of glycan processing ( enzymatic removal / addition of carbohydrate residues to the glycan ), which occurs in both the endoplastic reticulum and Golgi apparatus, is dispensable for isolated cells ( as evidence by survival with glycosides inhibitors ) but can lead to human disease ( congenital disorders of glycosylation ) and can be lethal in animal models. It is therefore likely that the fine processing of glycans is important for endogenous functionality, such as cell trafficking, but that this is likely to have been secondary to its role in host - pathogen interactions. A famous example of this latter effect is the ABO blood group system. Contents 1 Types of glycosylation 2 Monosaccharides 3 Examples 4 Hormones 5 Functions 6 Analysis 7 See also 8 Notes and references 9 External links Types of glycosylation There are several types of glycosylation, although the first two are the most common. In N - glycosylation, sugars are attached to nitrogen, typically on the amide side - chain of asparagine. In O - glycosylation, sugars are attached to oxygen, typically on serine or threonine, but also on tyrosine or non-canonical amino acids such as hydroxylysine & hydroxyproline. In P - glycosylation, sugars are attached to phosphorus on a phosphoserine. In C - glycosylation, sugars are attached directly to carbon, such as in the addition of mannose to tryptophan. In S - glycosylation, a beta - GlcNAc is attached to the sulfur atom of a cysteine residue. In glypiation, a GPI glycolipid is attached to the C - terminus of a polypeptide, serving as a membrane anchor. In glycation, also known as non-enzymatic glycosylation, sugars are covalently bonded to a protein or lipid molecule, without the controlling action of an enzyme, but through a Maillard reaction. Monosaccharides Eight sugars commonly found in glycoproteins. Monosaccharides commonly found in eukaryotic glycoproteins include : The principal sugars found in human glycoproteins Sugar Type Abbreviation β - D - Glucose Hexose Glc β - D - Galactose Hexose Gal β - D - Mannose Hexose Man α - L - Fucose Deoxyhexose Fuc N - Acetylgalactosamine Aminohexose GalNAc N - Acetylglucosamine Aminohexose GlcNAc N - Acetylneuraminic acid Aminononulosonic acid ( Sialic acid ) NeuNAc Xylose Pentose Xyl The sugar group ( s ) can assist in protein folding, improve proteins ' stability and are involved in cell signalling. Examples One example of glycoproteins found in the body is mucins, which are secreted in the mucus of the respiratory and digestive tracts. The sugars when attached to mucins give them considerable water - holding capacity and also make them resistant to proteolysis by digestive enzymes. Glycoproteins are important for white blood cell recognition. Examples of glycoproteins in the immune system are : molecules such as antibodies ( immunoglobulins ), which interact directly with antigens. molecules of the major histocompatibility complex ( or MHC ), which are expressed on the surface of cells and interact with T cells as part of the adaptive immune response. sialyl Lewis X antigen on the surface of leukocytes. H antigen of the ABO blood compatibility antigens. Other examples of glycoproteins include : gonadotropins ( luteinizing hormone a follicle - stimulating hormone ) glycoprotein IIb / IIIa, an integrin found on platelets that is required for normal platelet aggregation and adherence to the endothelium. components of the zona pellucida, which surrounds the oocyte, and is important for sperm - egg interaction. structural glycoproteins, which occur in connective tissue. These help bind together the fibers, cells, and ground substance of connective tissue. They may also help components of the tissue bind to inorganic substances, such as calcium in bone. Glycoprotein - 41 ( gp41 ) and glycoprotein - 120 ( gp120 ) are HIV viral coat proteins. Soluble glycoproteins often show a high viscosity, for example, in egg white and blood plasma. Miraculin, is a glycoprotein extracted from Synsepalum dulcificum a berry which alters human tongue receptors to recognize sour foods as sweet. Variable surface glycoproteins allow the sleeping sickness Trypanosoma parasite to escape the immune response of the host. The viral spike of the human immunodeficiency virus is heavily glycosylated. Approximately half the mass of the spike is glycosylation and the glycans act to limit antibody recognition as the glycans are assembled by the host cell and so are largely ' self '. Over time, some patients can evolve antibodies to recognise the HIV glycans and almost all so - called ' broadly neutralising antibodies ( bnAbs ) recognise some glycans. This is possible mainly because the unusually high density of glycans hinders normal glycan maturation and they are therefore trapped in the premature, high - mannose, state. This provides a window for immune recognition. In addition, as these glycans are much less variable than the underlying protein, they have emerged as promising targets for vaccine design. Hormones Hormones that are glycoproteins include : Follicle - stimulating hormone Luteinizing hormone Thyroid - stimulating hormone Human chorionic gonadotropin Alpha - fetoprotein Erythropoietin ( EPO ) Functions Some functions served by glycoproteins Function Glycoproteins Structural molecule Collagens Lubricant and protective agent Mucins Transport molecule Transferrin, ceruloplasmin Immunologic molecule Immunoglobulins, histocompatibility antigens Hormone Human chorionic gonadotropin ( HCG ), thyroid - stimulating hormone ( TSH ) Enzyme Various, e.g., alkaline phosphatase, patatin Cell attachment - recognition site Various proteins involved in cell -- cell ( e.g., sperm -- oocyte ), virus -- cell, bacterium -- cell, and hormone -- cell interactions Antifreeze protein Certain plasma proteins of coldwater fish Interact with specific carbohydrates Lectins, selectins ( cell adhesion lectins ), antibodies Receptor Various proteins involved in hormone and drug action Affect folding of certain proteins Calnexin, calreticulin Regulation of development Notch and its analogs, key proteins in development Hemostasis ( and thrombosis ) Specific glycoproteins on the surface membranes of platelets Analysis A variety of methods used in detection, purification, and structural analysis of glycoproteins are Some important methods used to study glycoproteins Method Use Periodic acid - Schiff stain Detects glycoproteins as pink bands after electrophoretic separation. Incubation of cultured cells with glycoproteins as radioactive decay bands Leads to detection of a radioactive sugar after electrophoretic separation. Treatment with appropriate endo - or exoglycosidase or phospholipases Resultant shifts in electrophoretic migration help distinguish among proteins with N - glycan, O - glycan, or GPI linkages and also between high mannose and complex N - glycans. Agarose - lectin column chromatography, lectin affinity chromatography To purify glycoproteins or glycopeptides that bind the particular lectin used. Lectin affinity electrophoresis Resultant shifts in electrophoretic migration help distinguish and characterize glycoforms, i.e. variants of a glycoprotein differing in carbohydrate. Compositional analysis following acid hydrolysis Identifies sugars that the glycoprotein contains and their stoichiometry. Mass spectrometry Provides information on molecular mass, composition, sequence, and sometimes branching of a glycan chain. It can also be used for site - specific glycosylation profiling. NMR spectroscopy To identify specific sugars, their sequence, linkages, and the anomeric nature of glycosidic chain. Multi-angle light scattering In conjunction with size - exclusion chromatography, UV / Vis absorption and differential refractometry, provides information on molecular mass, protein - carbohydrate ratio, aggregation state, size, and sometimes branching of a glycan chain. In conjunction with composition - gradient analysis, analyzes self - and hetero - association to determine binding affinity and stoichiometry with proteins or carbohydrates in solution without labeling. Dual Polarisation Interferometry Measures the mechanisms underlying the biomolecular interactions, including reaction rates, affinities and associated conformational changes. Methylation ( linkage ) analysis To determine linkage between sugars. Amino acid or cDNA sequencing Determination of amino acid sequence. See also Ero1 Female sperm storage Glycocalyx Glycome Glycopeptide Gp120 Gp41 Miraculin P - glycoprotein Proteoglycan Ribophorin Notes and references Jump up ^ Ruddock & Molinari ( 2006 ) Journal of Cell Science 119, 4373 -- 4380 Jump up ^ Funakoshi Y, Suzuki T ( January 2009 ). `` Glycobiology in the cytosol : The bitter side of a sweet world ''. Biochim. Biophys. Acta. 1790 ( 2 ) : 81 -- 94. doi : 10.1016 / j. bbagen. 2008.09. 009. PMID 18952151. Jump up ^ Stepper, Judith ; Shastri, Shilpa ; Loo, Trevor S. ; Preston, Joanne C. ; Novak, Petr ; Man, Petr ; Moore, Christopher H. ; Havlíček, Vladimír ; Patchett, Mark L. ( 2011 - 01 - 18 ). `` CysteineS - glycosylation, a new post-translational modification found in glycopeptide bacteriocins ''. FEBS Letters. 585 ( 4 ) : 645 -- 650. doi : 10.1016 / j. febslet. 2011.01. 023. ISSN 0014 - 5793. ^ Jump up to : Robert K. Murray, Daryl K. Granner & Victor W. Rodwell : `` Harper 's Illustrated Biochemistry 27th Ed. '', McGraw -- Hill, 2006 Jump up ^ Glycan classification SIGMA Jump up ^ Theerasilp S, Kurihara Y ( August 1988 ). `` Complete purification and characterization of the taste - modifying protein, miraculin, from miracle fruit ''. J. Biol. Chem. 263 ( 23 ) : 11536 -- 9. PMID 3403544. Jump up ^ Pritchard, Laura K. ; Vasiljevic, Snezana ; Ozorowski, Gabriel ; Seabright, Gemma E. ; Cupo, Albert ; Ringe, Rajesh ; Kim, Helen J. ; Sanders, Rogier W. ; Doores, Katie J. ( 2015 - 06 - 16 ). `` Structural Constraints Determine the Glycosylation of HIV - 1 Envelope Trimers ''. Cell Reports. 11 ( 10 ) : 1604 -- 1613. doi : 10.1016 / j. celrep. 2015.05. 017. ISSN 2211 - 1247. PMC 4555872. PMID 26051934. Jump up ^ Pritchard, Laura K. ; Spencer, Daniel I.R. ; Royle, Louise ; Bonomelli, Camille ; Seabright, Gemma E. ; Behrens, Anna - Janina ; Kulp, Daniel W. ; Menis, Sergey ; Krumm, Stefanie A. ( 2015 - 06 - 24 ). `` Glycan clustering stabilizes the mannose patch of HIV - 1 and preserves vulnerability to broadly neutralizing antibodies ''. Nature Communications. 6 : 7479. Bibcode : 2015NatCo... 6E7479P. doi : 10.1038 / ncomms8479. PMC 4500839. PMID 26105115. Jump up ^ Behrens, Anna - Janina ; Vasiljevic, Snezana ; Pritchard, Laura K. ; Harvey, David J. ; Andev, Rajinder S. ; Krumm, Stefanie A. ; Struwe, Weston B. ; Cupo, Albert ; Kumar, Abhinav ( 2016 - 03 - 10 ). `` Composition and Antigenic Effects of Individual Glycan Sites of a Trimeric HIV - 1 Envelope Glycoprotein ''. Cell Reports. 14 ( 11 ) : 2695 -- 2706. doi : 10.1016 / j. celrep. 2016.02. 058. ISSN 2211 - 1247. PMC 4805854. PMID 26972002. Jump up ^ Crispin, Max ; Doores, Katie J ( 2015 - 04 - 01 ). `` Targeting host - derived glycans on enveloped viruses for antibody - based vaccine design ''. Current Opinion in Virology. Viral pathogenesis Preventive and therapeutic vaccines. 11 : 63 -- 69. doi : 10.1016 / j. coviro. 2015.02. 002. PMC 4827424. PMID 25747313. ^ Jump up to : Maverakis E, Kim K, Shimoda M, Gershwin M, Patel F, Wilken R, Raychaudhuri S, Ruhaak LR, Lebrilla CB ( 2015 ). `` Glycans in the immune system and The Altered Glycan Theory of Autoimmunity ''. J Autoimmun. 57 ( 6 ) : 1 -- 13. doi : 10.1016 / j. jaut. 2014.12. 002. PMC 4340844. PMID 25578468. Jump up ^ Dell A ( 2001 ). `` Glycoprotein Structure Determination by Mass Spectrometry ''. Science. 291 ( 5512 ) : 2351 -- 2356. Bibcode : 2001Sci... 291.2351 D. doi : 10.1126 / science. 1058890. ISSN 0036 - 8075. External links Glycan Recognizing Proteins Structure of Glycoprotein and Carbohydrate Chain -- Home Page for Learning Environmental Chemistry Biochemistry 5thE 11.3. Carbohydrates Can Be Attached to Proteins to Form Glycoproteins Carbohydrate Chemistry and Glycobiology : A Web Tour SPECIAL WeB SUPPLEMENT Science 23 March 2001 Vol 291, Issue 5512, Pages 2263 -- 2502 Glycoproteins at the US National Library of Medicine Medical Subject Headings ( MeSH ) Emanual Maverakis et. al. `` Glycans in the immune system and The Altered Glycan Theory of Autoimmunity '' ( PDF ). Biological Importance of the glycosylation of a protein Protein, glycoconjugate : glycoproteins and glycopeptides Mucoproteins Mucin CD43 CD164 MUC1 MUC2 MUC3A MUC3B MUC4 MUC5AC MUC5B MUC6 MUC7 MUC8 MUC12 MUC13 MUC15 MUC16 MUC17 MUC19 MUC20 Other Haptoglobin Intrinsic factor Orosomucoid Peptidoglycan Phytohaemagglutinin Ovomucin Proteoglycans CS / DS Decorin Biglycan Versican HS / CS Testican Perlecan CS Chondroitin sulfate proteoglycans : Aggrecan Neurocan Brevican CD44 CSPG4 CSPG5 Platelet factor 4 Structural maintenance of chromosomes 3 KS Fibromodulin Lumican Keratocan HS Syndecan 1 Other Activin and inhibin ADAM Alpha 1 - antichymotrypsin Apolipoprotein H CD70 Asialoglycoprotein Avidin B - cell activating factor 4 - 1BB ligand Cholesterylester transfer protein Clusterin Colony - stimulating factor Hemopexin Lactoferrin Membrane glycoproteins Myelin protein zero Osteonectin Protein C Protein S Serum amyloid P component Sialoglycoprotein CD43 Glycophorin Glycophorin C Thrombopoietin Thyroglobulin Thyroxine - binding proteins Transcortin Tumor necrosis factor alpha Uteroglobin Vitronectin Metabolism : carbohydrate metabolism glycoprotein enzymes Anabolism Dolichol kinase GCS1 Oligosaccharyltransferase Catabolism Neuraminidase Beta - galactosidase Hexosaminidase mannosidase alpha - Mannosidase beta - mannosidase Aspartylglucosaminidase Fucosidase NAGA Transport SLC17A5 M6P tagging N - acetylglucosamine - 1 - phosphate transferase Lysosomal storage diseases : Inborn errors of carbohydrate metabolism ( Glycoproteinoses ) ( E77, 271.8 ) Anabolism Dolichol kinase deficiency Congenital disorder of glycosylation Post-translational modification of lysosomal enzymes Mucolipidosis : I - cell disease ( ML II ) Pseudo-Hurler polydystrophy ( ML III ) Catabolism Aspartylglucosaminuria Fucosidosis mannosidosis Alpha - mannosidosis Beta - mannosidosis Sialidosis Schindler disease Other solute carrier family ( Salla disease ) Galactosialidosis GND : 4071905 - 4 NDL : 00573418 Molecular and cellular biology portal Retrieved from `` https://en.wikipedia.org/w/index.php?title=Glycoprotein&oldid=855120286 '' Categories : Glycoproteins Carbohydrate chemistry Hidden categories : Use dmy dates from April 2017 All articles with specifically marked weasel - worded phrases Articles with specifically marked weasel - worded phrases from March 2017 All articles with unsourced statements Articles with unsourced statements from March 2017 Articles with unsourced statements from December 2007 Wikipedia articles with GND identifiers Wikipedia articles with NDL identifiers Talk Contents About Wikipedia Asturianu Беларуская Bosanski Català Čeština Dansk Deutsch Eesti Español Euskara فارسی Français Galego Bahasa Indonesia Italiano עברית Қазақша Кыргызча Lietuvių Magyar Македонски Bahasa Melayu Nederlands 日本 語 Norsk Norsk nynorsk Occitan Polski Português Română Русский Scots Simple English Slovenščina Српски / srpski Srpskohrvatski / српскохрватски Suomi Svenska தமிழ் ไทย Türkçe Українська Tiếng Việt 中文 36 more Edit links This page was last edited on 16 August 2018, at 02 : 43 ( UTC ). 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Question: where are sugars added to proteins to form glycoprotein
Answer: glycation