NationMaster - Encyclopedia: Glycosylation

Glycosylation is the process or result of addition of saccharides to proteins and lipids. The process is one of four principal co-translational and post-translational modification steps in the synthesis of membrane and secreted proteins and the majority of proteins synthesized in the rough ER undergo glycosylation. It is an enzyme-directed site-specific process, as opposed to the non-enzymatic chemical reaction of glycation. Two types of glycosylation exist: N-linked glycosylation to the amide nitrogen of asparagine side chains and O-linked glycosylation to the hydroxy oxygen of serine and threonine side chains. an essential structural component of living cells and source of energy for animals; includes simple sugars with small molecules as well as macromolecular substances; are classified according to the number of monosaccharide groups they contain. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Some common lipids. ... Posttranslational modification means the chemical modification of a protein after its translation. ... The endoplasmic reticulum or ER is an organelle found in all eukaryotic cells that is an interconnected network of tubules, vesicles and cisternae that is responsible for several specialized functions: Protein translation, folding, and transport of proteins to be used in the cell membrane (e. ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... Glycation is the result of a sugar-reducing molecule, such as fructose or glucose, bonding to a protein or lipid molecule without the controlling action of an enzyme. ... Amide functional group Amides possess a conjugated system spread over the O, C and N atoms, consisting of molecular orbitals occupied by delocalized electrons. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... For other articles using the abbreviation or acronym asn see ASN. Asparagine is one of the 20 most common natural amino acids on Earth. ... The term Side chain can have different meanings depending on the context: In chemistry and biochemistry a side chain is a part of a molecule attached to a core structure. ... This prefix in chemical nomenclature indicates the presence of a hydroxyl functional group (-OH). ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... Serine (IPA ), organic compound, one of the 20 amino acids commonly found in animal proteins. ... Threonine is one of the 20 natural amino acids. ...

Purpose

The polysaccharide chains attached to the target proteins serve various functions. For instance, some proteins do not fold correctly unless they are glycosylated first. Also, polysaccharides linked at the amide nitrogen of asparagine in the protein confer stability on some secreted glycoproteins. Experiments have shown that glycosylation in this case is not a strict requirement for proper folding, but the unglycosylated protein degrades quickly. Glycosylation may play a role in cell-cell adhesion (a mechanism employed by cells of the immune system), as well. General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... For other articles using the abbreviation or acronym asn see ASN. Asparagine is one of the 20 most common natural amino acids on Earth. ... A scanning electron microscope image of a single neutrophil (yellow), engulfing anthrax bacteria (orange). ...

Mechanisms

There are various mechanisms for glycosylation, although all share several common features:

N-linked glycosylation

N-linked glycosylation is important for the folding of some of eukaryotic proteins. The N-linked glycosylation process occurs in eukaryotes and widely in archaea, but very rarely in bacteria. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Dolichol is an isoprenoid compound similar to cholesterol. ... Kingdoms Eukaryotes are organisms with complex cells, in which the genetic material is organized into membrane-bound nuclei. ... Phyla Crenarchaeota Euryarchaeota Korarchaeota Nanoarchaeota ARMAN The Archaea (), or archaebacteria, are a major group of microorganisms. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ...

For N-linked oligosaccharides, a 14-sugar precursor is first added to the asparagine in the polypeptide chain of the target protein. The structure of this precursor is common to most eukaryotes, and contains 3 glucose, 9 mannose, and 2 N-acetylglucosamine molecules. A complex set of reactions attaches this branched chain to a carrier molecule called dolichol, and then it is transferred to the appropriate point on the polypeptide chain as it is translocated into the ER lumen. Kingdoms Animalia - Animals Fungi Plantae - Plants Chromalveolata Protista Alternative phylogeny Unikonta Opisthokonta Metazoa Choanozoa Eumycota Amoebozoa Bikonta Apusozoa Cabozoa Rhizaria Excavata Corticata Archaeplastida Chromalveolata Animals, plants, fungi, and protists are eukaryotes (IPA: ), organisms whose cells are organized into complex structures by internal membranes and a cytoskeleton. ... Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. ... D and L forms Haworth projection of mannose in its Î±-D-mannopyranose form. ... Dolichol is an isoprenoid compound similar to cholesterol. ...

There are two major types of N-linked saccharides: high-mannose oligosaccharides, and complex oligosaccharides.

Proteins can be glycosylated by both types of oligos on different portions of the protein. Whether an oligosaccharide is high-mannose or complex is thought to depend on its accessibility to saccharide-modifying proteins in the Golgi. If the saccharide is relatively inaccessible, it will most likely stay in its original high-mannose form. If it is accessible, then it is likely that many of the mannose residues will be cleaved off and the saccharide will be further modified by the addition of other types of group as discussed above. Micrograph of Golgi apparatus, visible as a stack of semicircular black rings near the bottom. ...

The oligosaccharide chain is attached by oligosaccharyltransferase to asparagine occurring in the tripeptide sequence Asn-X-Ser or Asn-X-Thr, where X could be any amino acid except Pro. This sequence is known as a glycosylation sequon. After attachment, once the protein is correctly folded, the three glucose residues are removed from the chain and the protein is available for export from the ER. The glycoprotein thus formed is then transported to the Golgi where removal of further mannose residues may take place. However, glycosylation itself does not seem to be as necessary for correct transport targeting of the protein, as one might think. Studies involving drugs that block certain steps in glycosylation, or mutant cells deficient in a glycosylation enzyme, still produce otherwise-structurally-normal proteins that are correctly targeted, and this interference does not seem to interfere severely with the viability of the cells. Mature glycoproteins may contain a variety of oligomannose N-linked oligosaccharides containing between 5 and 9 mannose residues. Further removal of mannose residues leads to a 'core' structure containing 3 mannose, and 2 N-acetylglucosamine residues, which may then be elongated with a variety of different monosaccharides including galactose, N-acetylglucosamine, N-acetylgalactosamine, fucose and sialic acid. An oligosaccharide is a saccharide polymer containing a small number (typically three to six) of component sugars, also known as simple sugars. ... Oligosaccharyltransferase or OST (EC 2. ... For other articles using the abbreviation or acronym asn see ASN. Asparagine is one of the 20 most common natural amino acids on Earth. ... Peptides (from the Greek Ï€ÎµÏ€Ï„Î¿Ï‚, digestible), are the family of short molecules formed from the linking, in a defined order, of various Î±-amino acids. ... Serine (IPA ), organic compound, one of the 20 amino acids commonly found in animal proteins. ... Threonine is one of the 20 natural amino acids. ... This article is about the class of chemicals. ... Proline is an Î±-amino acid with the chemical formula HO2CCH(NH[CH2)3]. L-Proline is one of the twenty DNA-encoded amino acids. ... D and L forms Haworth projection of mannose in its Î±-D-mannopyranose form. ... Galactose (also called brain sugar) is a type of sugar found in dairy products, in sugar beets and other gums and mucilages. ... N-Acetylglucosamine (N-Acetyl-D-Glucosamine, or GlcNAc, or NAG) is a monosaccharide derivative of glucose. ... ... Fucose is a hexose sugar with the chemical formula C6H12O5. ... Sialic acid is a generic term for the N- or O-substituted derivatives of neuraminic acid, a nine-carbon monosaccharide. ...

O-linked glycosylation

O-N-acetylgalactosamine (O-GalNAc)

O-linked glycosylation occurs at a later stage during protein processing, probably in the Golgi apparatus. This is the addition of N-acetyl-galactosamine to serine or threonine residues by the enzyme UDP-N-acetyl-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase (EC 2.4.1.41), followed by other carbohydrates (such as galactose and sialic acid). This process is important for certain types of proteins such as proteoglycans, which involves the addition of glycosaminoglycan chains to an initially unglycosylated "proteoglycan core protein." These additions are usually serine O-linked glycoproteins, which seem to have one of two main functions. One function involves secretion to form components of the extracellular matrix, adhering one cell to another by interactions between the large sugar complexes of proteoglycans. The other main function is to act as a component of mucosal secretions, and it is the high concentration of carbohydrates that tends to give mucus its "slimy" feel. Proteins that circulate in the blood are not normally O-glycosylated, with the exception of IgA1 and IgD (two types of antibody) and C1-inhibitor. Micrograph of Golgi apparatus, visible as a stack of semicircular black rings near the bottom. ... Serine (IPA ), organic compound, one of the 20 amino acids commonly found in animal proteins. ... Threonine is one of the 20 natural amino acids. ... The Enzyme Commission number (EC number) is a numerical classification scheme for enzymes, based on the chemical reactions they catalyze. ... Galactose (also called brain sugar) is a type of sugar found in dairy products, in sugar beets and other gums and mucilages. ... Sialic acid is a generic term for the N- or O-substituted derivatives of neuraminic acid, a nine-carbon monosaccharide. ... Proteoglycans represent a special class of glycoprotein that are heavily glycosylated. ... Illustration depicting extracellular matrix (basement membrane and interstitial matrix) in relation to epithelium, endothelium and connective tissue In biology, the extracellular matrix (ECM) is the extracellular part of animal tissue that usually provides structural support to the cells in addition to performing various other important functions. ... IGA may stand for: Koji Igarashi, a video game producer Interactive genetic algorithm International Geothermal Association Independent Glass Association International Gothic Association International Gamers Award International Goat Association Irish Games Association Irish Geological Association ImmunoGlobulin A - see IgA nephritis which is a renal disease IGA (supermarkets) Independent Grocers Association or... Schematic of antibody binding to an antigen An antibody is a protein complex used by the immune system to identify and neutralize foreign objects like bacteria and viruses. ... C1-inhibitor (C1inh) is a serine protease inhibitor (serpin) protein, the main function of which is inhibition of the complement system. ...

O-fucose

O-fucose is added between the second and third conserved cysteines of EGF-like repeats in the Notch protein, and possibly other substrates by GDP-fucose protein O-fucosyltransferase 1, and to Thrombospondin repeats by GDP-fucose protein O-fucosyltransferase 2. In the case of EGF-like repeats, the O-fucose may be further elongated to a tetrasaccharide by sequential addition of N-acetylglucosamine (GlcNAc), galactose, and sialic acid, and for Thrombospondin repeats, may be elongated to a disaccharide by the addition of glucose. Both of these fucosyltransferases have been localized to the endoplasmic reticulum, which is unusual for glycosyltransferases, most of which function in the Golgi apparatus. Notch can refer to: a mountain pass Notch signaling This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... GDP-fucose protein O-fucosyltransferase 1 (OFucT1) is an enzyme responsible for adding fucose sugars in O linkage to serine or threonine residues between the second and third conserved cysteines in EGF-like repeats on the Notch protein. ... Thrombospondins (TSP) are secreted proteins with the ability to inhibit angiogenesis. ... GDP-fucose protein O-fucosyltransferase 2 (OFucT2) is an enzyme responsible for adding fucose sugars in O linkage to serine or threonine residues in Thrombospondin repeats. ... Fucose is a hexose sugar with the chemical formula C6H12O5. ... N-Acetylglucosamine (N-Acetyl-D-Glucosamine, or GlcNAc, or NAG) is a monosaccharide derivative of glucose. ... Galactose (also called brain sugar) is a type of sugar found in dairy products, in sugar beets and other gums and mucilages. ... Sialic acid is a generic term for the N- or O-substituted derivatives of neuraminic acid, a nine-carbon monosaccharide. ... Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. ... The endoplasmic reticulum or ER is an organelle found in all eukaryotic cells that is an interconnected network of tubules, vesicles and cisternae that is responsible for several specialized functions: Protein translation, folding, and transport of proteins to be used in the cell membrane (e. ... In cell biology, the Golgi apparatus, Golgi body, Golgi complex, or dictyosome is an organelle found in most eukaryotic cells, including those of plants, animals, and fungi. ...

O-glucose

O-glucose is added between the first and second conserved cysteines of EGF-like repeats in the Notch protein, and possibly other substrates by an unidentified O-glucosyltransferase. Notch can refer to: a mountain pass Notch signaling This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ...

O-N-acetylglucosamine (O-GlcNAc)

O-GlcNAc is added to serines or threonines by O-GlcNAc transferase. O-GlcNAc appears to occur on serines and threonines that would otherwise be phosphorylated by serine/threonine kinases. Thus, if phosphorylation occurs, O-GlcNAc does not, and vice versa. This is an incredibly important finding because phosphorylation/dephosphorylation has become a scientific paradigm for the regulation of signaling within cells. A massive amount of cancer research is focused on phosphorylation. Ignoring the involvement of this form of glycosylation which clearly appears to act in concert with phosphorylation means that a lot of current research is missing at least half of the picture. O-GlcNAc addition and removal also appear to be key regulators of the pathways which are deregulated in diabetes mellitus. The gene encoding the O-GlcNAc removal enzyme has been linked to non-insulin dependent diabetes mellitus. It is the terminal step in a nutrient sensing hexosamine signaling pathway. A phosphorylated serine residue Phosphorylation is the addition of a phosphate (PO4) group to a protein or a small molecule or the introduction of a phosphate group into an organic molecule. ... Chemical structure of Î±-D- glucosamine. ...

GPI anchor

A special form of glycosylation is the GPI anchor. This form of glycosylation functions to attach a protein to a hydrophobic lipid anchor, via a glycan chain. (see also prenylation) A GPI anchor (phosphatidyl-inositol glycane) is a common modification of the C-terminus of membrane-attached proteins. ... In chemistry, hydrophobic or lipophilic species, or hydrophobes, tend to be electrically neutral and nonpolar, and thus prefer other neutral and nonpolar solvents or molecular environments. ... Prenylation or isoprenylation is the addition of hydrophobic molecules to a protein to facilitate its attachment to the cell membrane. ...

C-mannosylation

A mannose sugar is added to tryptophan residues in Thrombospondin repeats. This is an unusual modification both because the sugar is linked to a carbon rather than a reactive atom like a nitrogen or oxygen and because the sugar is linked to a tryptophan residue rather than an asparagine or serine/threonine. D and L forms Haworth projection of mannose in its Î±-D-mannopyranose form. ... Tryptophan is an essential amino acid involved in human nutrition. ... Thrombospondins (TSP) are secreted proteins with the ability to inhibit angiogenesis. ... For other uses, see Carbon (disambiguation). ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... Tryptophan is an essential amino acid involved in human nutrition. ... For other articles using the abbreviation or acronym asn see ASN. Asparagine is one of the 20 most common natural amino acids on Earth. ... Serine (IPA ), organic compound, one of the 20 amino acids commonly found in animal proteins. ... Threonine is one of the 20 natural amino acids. ...

See also

Glycation is the result of a sugar-reducing molecule, such as fructose or glucose, bonding to a protein or lipid molecule without the controlling action of an enzyme. ... It has been suggested that this article or section be merged with Glycation#Exogenous. ...

External links

Category: Posttranslational modification A protein primary structure is a chain of amino acids. ... Posttranslational modification is the chemical modification of a protein after its translation. ... An overview of protein synthesis. ... A peptide bond is a chemical bond that is formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a molecule of water (H2O). ... Proteolysis is the directed degradation (digestion) of proteins by cellular enzymes called proteases or by intramolecular digestion. ... In chemistry racemization refers to partial conversion of one enantiomer into another. ... The N-terminal end refers to the extremity of a protein or polypeptide terminated by an amino acid with a free amine group (NH2). ... Acetylation describes a reaction, usually with acetic acid, that introduces an acetyl functional group into an organic compound. ... Categories: | | ... This article needs to be wikified. ... Pyroglutamic acid is an uncommon amino acid found in bacteriorhodopsin. ... Methylation is a term used in the chemical sciences to denote the attachment or substitution of a methyl group on various substrates. ... Glycation is the result of a sugar-reducing molecule, such as fructose or glucose, bonding to a protein or lipid molecule without the controlling action of an enzyme. ... This article needs to be wikified. ... The C-terminal end refers to the extremity of a protein or polypeptide terminated by an amino acid with a free carboxyl group (COOH). ... Amide functional group In chemistry, an amide is one of two kinds of compounds: the organic functional group characterized by a carbonyl group (C=O) linked to a nitrogen atom (N), or a compound that contains this functional group (pictured to the right); or a particular kind of nitrogen anion. ... A GPI anchor or glycosylphosphatidylinositol is a common posttranslational modification of the C-terminus of membrane-attached proteins. ... // Background Ubiquitylation, also termed ubiquitination, refers to the process particular to eukaryotes whereby a protein is post-translationally modified by covalent attachment of a small protein. ... Small Ubiquitin-related Modifier or SUMO proteins are a family of small proteins that are covalently attached to and detached from other proteins in cells to modify their function. ... Lysine is one of the 20 amino acids normally found in proteins. ... Methylation is a term used in the chemical sciences to denote the attachment or substitution of a methyl group on various substrates. ... Acetylation describes a reaction, usually with acetic acid, that introduces an acetyl functional group into an organic compound. ... In chemistry, acylation is the process of adding an acyl group to a compound. ... Hydroxylation is any chemical process that introduces one or more hydroxyl groups (-OH) into a compound (or radical) thereby oxidising it. ... Ubiquitin is a very conserved small regulatory protein that is ubiquitous in eukaryotes. ... Small Ubiquitin-related Modifier or SUMO proteins are a family of small proteins that are covalently attached to and detached from other proteins in cells to modify their function. ... A desmosine cross-link is formed when three allysyl side chains plus one unaltered lysl side chain from the same or neighbouring polypeptides. ... ADP ribose ADP-ribosylation is a posttranslational modification of proteins that involves the addition of one or more ADP and ribose moieties. ... Deamination is the removal of an amine group from a molecule. ... Oxidative deamination is a form of deamination which generates oxoacids in the liver. ... Cysteine is a naturally occurring, sulfur-containing amino acid that is found in most proteins, although only in small quantities. ... In chemistry, a disulfide bond is a single covalent bond derived from the coupling of thiol groups. ... Prenylation or isoprenylation is the addition of hydrophobic molecules to a protein to facilitate its attachment to the cell membrane. ... Palmitoylation is the covalent attachment of fatty acids to cysteine residues of membrane proteins [1] ^ Linder, M.E. (2000). ... Serine (IPA ), organic compound, one of the 20 amino acids commonly found in animal proteins. ... Threonine is one of the 20 natural amino acids. ... A phosphorylated serine residue Phosphorylation is the addition of a phosphate (PO4) group to a protein or a small molecule or the introduction of a phosphate group into an organic molecule. ... Tyrosine (from the Greek tyros, meaning cheese, as it was first discovered in 1846 by German chemist Justus von Liebig in the protein casein from cheese[1][2]), 4-hydroxyphenylalanine, or 2-amino-3(4-hydroxyphenyl)-propanoic acid, is one of the 20 amino acids that are used by cells... A phosphorylated serine residue Phosphorylation is the addition of a phosphate (PO4) group to a protein or a small molecule or the introduction of a phosphate group into an organic molecule. ... Tyrosine sulfation is a posttranslational modification where a sulfate group is added to a tyrosine residue of a protein molecule. ... Structure of porphine, the simplest porphyrin. ... Riboflavin Flavin is a vaginal ring whose biochemical smell is pungent. ... The initialism GFP may refer to Green fluorescent protein, a fluorescent marker frequently used in biology. ... For other articles using the abbreviation or acronym asn see ASN. Asparagine is one of the 20 most common natural amino acids on Earth. ... Deamidation reaction of Asn-Gly (top right) to Asp-Gly (at left) or iso(Asp)-Gly (in green at bottom right). ... Aspartic acid, also known as aspartate, the name of its anion, is one of the 20 natural proteinogenic amino acids which are the building blocks of proteins. ... Deamidation reaction of Asn-Gly (top right) to Asp-Gly (at left) or iso(Asp)-Gly (in green at bottom right). ... Glutamine is one of the 20 amino acids encoded by the standard genetic code. ... Glutamate is the anion of glutamic acid. ... A carboxyl or carboxylic group is a functional group consisting of a carbon atom doubly bonded to an oxygen atom and single-bonded to a hydroxyl (-OH) group. ... A form of reversible posttranslational modification of glutamate residues seen for example in alpha and beta tubulins, nucleosome assembly proteins NAP1 and NAP2. ... Polyglycylation is a form of posttranslational modification of glutamate residues of the carboxyl-terminal region tubulin in certain microtubules (eg axonemal) originally discovered in paramecium[1], and later shown in mammalian neurons as well[2]. ^ Redeker, V., Levilliers, N., Schmitter, J.M., Le Caer, J.P., Rossier, J., Adoutte, A... Arginine (abbreviated as Arg or R)[1] is an Î±-amino acid. ... Citrullination or deimination is the term used for the post-translational modification of the amino acid arginine in a protein into the amino acid citrulline. ... Methylation is a term used in the chemical sciences to denote the attachment or substitution of a methyl group on various substrates. ... Proline is an Î±-amino acid with the chemical formula HO2CCH(NH[CH2)3]. L-Proline is one of the twenty DNA-encoded amino acids. ... Hydroxylation is any chemical process that introduces one or more hydroxyl groups (-OH) into a compound (or radical) thereby oxidising it. ... In chemistry, an amino acid is any molecule that contains both amino and carboxylic acid functional groups. ... A representation of the 3D structure of the Myoglobin protein. ...

Contents

Purpose GA_googleFillSlot("encyclopedia_square");