Glycoproteins are proteins Proteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues. The sequence of amino acids in a protein is defined by the sequence of a gene, which is encoded that contain oligosaccharide An oligosaccharide is a saccharide polymer containing a small number of component sugars, also known as simple sugars (monosaccharides). The name is derived from the Greek word oligos, meaning "a few", and from the Latin/Greek word sacchar which means "sugar". Oligosaccharides can have many functions; for example, they are chains (glycans The term glycan refers to a polysaccharide or oligosaccharide. Glycan may also be used to refer to the carbohydrate portion of a glycoconjugate, such as a glycoprotein, glycolipid, or a proteoglycan. Glycans usually consist solely of O-glycosidic linkages of monosaccharides. For example, cellulose is a glycan composed of beta-1,4-linked D-glucose,) covalently attached to polypeptide Peptides are short polymers formed from the linking, in a defined order, of α-amino acids. The link between one amino acid residue and the next is called an amide bond or a peptide bond side-chains. The carbohydrate is attached to the protein in a cotranslational Translation is the first stage of protein biosynthesis . In translation, messenger RNA (mRNA) produced in transcription is decoded to produce a specific amino acid chain, or polypeptide, that will later fold into an active protein. Translation occurs in the cell's cytoplasm, where the large and small subunits of the ribosome are located, and bind or posttranslational modification Posttranslational modification is the chemical modification of a protein after its translation. It is one of the later steps in protein biosynthesis for many proteins. This process is known as glycosylation Glycosylation is the enzymatic process that links saccharides to produce glycans, attached to proteins, lipids, or other organic molecules. This enzymatic process produces one of the fundamental biopolymers found in cells . Glycosylation is a form of co-translational and post-translational modification. Glycans serve a variety of structural and. In proteins that have segments extending extracellularly, the extracellular segments are often glycosylated. Glycoproteins are often important integral membrane proteins, where they play a role in cell-cell interactions. Glycoproteins also occur in the cytosol The cytosol or intracellular fluid is the liquid found inside cells. In eukaryotes this liquid is separated by cell membranes from the contents of the organelles suspended in the cytosol, such as the mitochondrial matrix inside the mitochondrion. The entire contents of a eukaryotic cell within cell membrane, minus the contents of the cell nucleus,, but their functions and the pathways producing these modifications in this compartment are less well-understood.[2]
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N-glycosylation and O-glycosylation
There are two types of glycoproteins:
- In N-glycosylation Glycosylation is the enzymatic process that links saccharides to produce glycans, attached to proteins, lipids, or other organic molecules. This enzymatic process produces one of the fundamental biopolymers found in cells . Glycosylation is a form of co-translational and post-translational modification. Glycans serve a variety of structural and (see on the right), the addition of sugar chains can happen at the amide nitrogen on the side chain of the asparagine Asparagine is one of the 20 most common natural amino acids on Earth. It has carboxamide as the side chain's functional group. It is not an essential amino acid. Its codons are AAU and AAC.
- In O-glycosylation Glycosylation is the enzymatic process that links saccharides to produce glycans, attached to proteins, lipids, or other organic molecules. This enzymatic process produces one of the fundamental biopolymers found in cells . Glycosylation is a form of co-translational and post-translational modification. Glycans serve a variety of structural and, the addition of sugar chains can happen on the hydroxyl In chemistry, hydroxyl is a compound containing an oxygen atom bound covalently with a hydrogen atom. The neutral form of this group is a hydroxyl radical. The hydroxyl anion is called hydroxide; it is a diatomic ion with a single negative electronic charge. In discussions of synthetic methods in organic chemistry the hydroxyl group (–OH) is oxygen Oxygen (pronounced /ˈɒksɨdʒɨn/, OK-si-jin, from the Greek roots ὀξύς (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter), is the element with atomic number 8 and represented by the symbol O. It is a member of the chalcogen group on the periodic table, and is a highly on the side chain of hydroxylysine, hydroxyproline -4-Hydroxyproline, or L-hydroxyproline (C5H9O3N), is a common proteinogenic amino acid, abbreviated as HYP, e.g., in Protein Data Bank, serine Serine is an organic compound with the formula H , or threonine Threonine is an α-amino acid with the chemical formula HO2CCH(NH2)CH(OH)CH3. Its codons are ACU, ACA, ACC, and ACG. This essential amino acid is classified as polar. Together with serine and tyrosine, threonine is one of three proteinogenic amino acids bearing an alcohol group.
Monosaccharides
The eight sugars contained in glycoproteins.Monosaccharides commonly found in eukaryotic glycoproteins include:[3]
The sugar group(s) can assist in protein folding Protein folding is the physical process by which a polypeptide folds into its characteristic and functional three-dimensional structure from random coil. Each protein exists as an unfolded polypeptide or random coil when translated from a sequence of mRNA to a linear chain of amino acids. This polypeptide lacks any developed three-dimensional or improve proteins' stability.
Examples
One example of glycoproteins found in the body is mucins Mucins are a family of high molecular weight, heavily glycosylated proteins produced by epithelial tissues in most metazoans. Mucins' key characteristic is their ability to form gels; therefore they are a key component in most gel-like secretions, serving functions from lubrication to cell signalling to forming chemical barriers. They often take, which are secreted in the mucus of the respiratory and digestive tracts. The sugars attached to mucins give them considerable water-holding capacity and also make them resistant to proteolysis Proteolysis is the directed degradation of proteins by cellular enzymes called proteases or by intramolecular digestion by digestive enzymes.
Glycoproteins are important for white blood cell White blood cells , or leukocytes (also spelled "leucocytes"), are cells of the immune system defending the body against both infectious disease and foreign materials. Five different and diverse types of leukocytes exist, but they are all produced and derived from a multipotent cell in the bone marrow known as a hematopoietic stem cell recognition, especially in mammals Mammals are a class of vertebrate, air-breathing animals whose females are characterized by the possession of mammary glands while both males and females are characterized by hair and/or fur, three middle ear bones used in hearing, and a neocortex region in the brain. Some mammals have sweat glands, but most do not.[citation needed] Examples of glycoproteins in the immune system An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own healthy cells and tissues in order to function are:
- molecules such as antibodies Antibodies are gamma globulin proteins that are found in blood or other bodily fluids of vertebrates, and are used by the immune system to identify and neutralize foreign objects, such as bacteria and viruses. They are typically made of basic structural units—each with two large heavy chains and two small light chains—to form, for example, (immunoglobulins), which interact directly with antigens An antigen is a molecule recognized by the immune system. Originally the term came from antibody generator and was a molecule that binds specifically to an antibody, but the term now also refers to any molecule or molecular fragment that can be bound by a major histocompatibility complex and presented to a T-cell receptor. "Self"
- molecules of the major histocompatibility complex The major histocompatibility complex is a large genomic region or gene family found in most vertebrates. It is the most gene-dense region of the mammalian genome and plays an important role in the immune system and autoimmunity. The diversity of MHC is important in the immune diversity in the population. The proteins encoded by the MHC are (or MHC), which are expressed on the surface of cells and interact with T cells T cells or T lymphocytes belong to a group of white blood cells known as lymphocytes, and play a central role in cell-mediated immunity. They can be distinguished from other lymphocyte types, such as B cells and natural killer cells by the presence of a special receptor on their cell surface called T cell receptors . The abbreviation T, in T cell, as part of the adaptive immune response.
Other examples of glycoproteins include:
- glycoprotein IIb/IIIa In medicine, glycoprotein IIb/IIIa, also gpIIb/IIIa, is an integrin found on platelets. It is a receptor for fibrinogen and aids in platelet activation. The complex is formed via calcium-dependent association of gpIIb and gpIIIa, a required step in normal platelet aggregation and endothelial adherence. Platelet activation by ADP leads to a, an integrin found on platelets Platelets, or thrombocytes , are small, irregularly-shaped anuclear cell fragments (i.e. cells that do not have a nucleus containing DNA), 2-3 µm in diameter, which are derived from fragmentation of precursor megakaryocytes. The average lifespan of a platelet is normally just 5 to 9 days. Platelets play a fundamental role in hemostasis and are a that is required for normal platelet aggregation and adherence to the endothelium The endothelium is the thin layer of cells that line the interior surface of blood vessels, forming an interface between circulating blood in the lumen and the rest of the vessel wall. These cells are called endothelial cells. Endothelial cells line the entire circulatory system, from the heart to the smallest capillary. These cells reduce.
- components of the zona pellucida The zona pellucida is a glycoprotein membrane surrounding the plasma membrane of an oocyte. It is a vital constitutive part of the latter, external but not extraneous to it. The zona pellucida first appears in multilaminar primary oocytes, which surrounds the oocyte An oocyte, ovocyte, or rarely ocyte, is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in the ovary during female gametogenesis. The female germ cells produce a primordial germ cell which undergoes a mitotic division to form an oogonium. During oogenesis the, and is important for sperm-egg interaction.
- structural glycoproteins, which occur in connective tissue Connective tissue is a form of fibrous tissue.. It is one of the four types of tissue in traditional classifications. These help bind together the fibers, cells, and ground substance of connective tissue Connective tissue is a form of fibrous tissue.. It is one of the four types of tissue in traditional classifications. They may also help components of the tissue bind to inorganic substances, such as calcium Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth most abundant element by mass in the Earth's crust. Calcium is also the fifth most abundant dissolved ion in seawater by both molarity and mass, after sodium, chloride, in bone Bones are rigid organs that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue. Because bones come in a variety of shapes and have a complex internal and external structure.
- Glycoprotein-41 (gp41) and glycoprotein-120 (gp120) are HIV viral coat proteins.
Soluble glycoproteins often show a high viscosity Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. For example, high-viscosity felsic magma will create a tall, steep stratovolcano, because it cannot flow far before it cools, while low-viscosity mafic lava will create a wide, shallow-sloped shield volcano. All real fluids have some, for example, in egg white Egg white is the common name for the clear liquid contained within an egg. It is the cytoplasm of the egg, which until fertilization is a single cell (including the yolk). It consists mainly of about 15% proteins dissolved in water. Its primary natural purpose is to protect the egg yolk and provide additional nutrition for the growth of the embryo, and blood plasma Blood plasma is the yellow liquid component of blood, in which the blood cells in whole blood would normally be suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid. It is mostly water and contains dissolved proteins, glucose, clotting factors, mineral ions, hormones and carbon.
Hormones
- Follicle-stimulating hormone
- Luteinizing hormone
- Thyroid-stimulating hormone
- Human chorionic gonadotropin
- Alpha-fetoprotein
- Erythropoietin (EPO)
Functions
| Function | Glycoproteins |
|---|---|
| Structural molecule | Collagens |
| Lubricant and protective agent | Mucins |
| Transport molecule | Transferrin, ceruloplasmin |
| Immunologic molecule | Immunoglobins, histocompatibility antigens |
| Hormone | Human chorionic gonadotropin (HCG), thyroid-stimulating hormone (TSH) |
| Enzyme | Various, eg, alkaline phosphatase |
| Cell attachment-recognition site | Various proteins involved in cell-cell (eg, sperm-oocyte), virus-cell, bacterium-cell, and hormone cell interactions |
| Antifreeze | 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[6][7]
| 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. |
| NMR spectroscopy | To identify specific sugars, their sequence, linkages, and the anomeric nature of glycosidic chain. |
| 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
References
| Constructs such as ibid. and loc. cit. are discouraged by Wikipedia's style guide for footnotes as they are easily broken. Please improve this article by replacing them with named references (), or an abbreviated title. |
- ^ Ruddock & Molinari (2006) Journal of Cell Science 119, 4373-4380
- ^ 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.
- ^ Robert K. Murray, Daryl K. Granner & Victor W. Rodwell: "Harper's Illustrated Biochemistry 27th Ed.", p. 526, McGraw-Hill, 2006
- ^ https://www.sigmaaldrich.com/img/assets/15880/glycan_classification.pdf
- ^ Ibid., p. 524
- ^ Ibid., p. 525
- ^ Anne Dell, Howard R Morris: "Glycoprotein structure determination by mass spectrometry", Science 291(5512), 2351-2356 (2001), Review
External links
- 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
- MeSH Glycoproteins
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Categories: Glycoproteins | Carbohydrates | Carbohydrate chemistry
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Pharmafocus, UK
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in varying amounts 2 Hybrid type contains various sugars and amino sugars 3 Complex type is similar to the hybrid type but in addition contains sialic acids to varying degrees Open squares GlcNAc open circles mannose open diamonds galactose filled squares fucose filled triangles sialic acid the greek symbols and followed by numbers refers to
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2008-07-30 13:47:40
(2008) Definition of a conserved immunodominant domain on HCV E2 . glycoprotein. by neutralizing human monoclonal antibodies. The Journal of Virology, 82 (12). pp. 6061-6066. ISSN 0022-538X. Full text not available from this repository. ...
Q. Glycoproteins are the cell's highly specific biological markers that aid cellular interactions. Definite changes can occur in the cell's glycoprotein that are being transformed into a cancerous cell. What would be a true statement regarding this? A. This would prevent the invasion of toxic organisms B. The cancer cell's glycprotein changes faster than the immune system's ability to keep up C. Glycoproteins allow non-specific ions to pass D. Mitochondria help the cell's glycoproteins fight infection
Asked by Entrepreneur - Sun Oct 29 18:22:30 2006 - - 1 Answers - 0 Comments
A. The answer should be B when a cell becomes a cancer cell, our immune system such as the CD8+ T cells do sometimes recognise them as foreign, however the activation of immune cells (CD4, and B cells) by these cancer cells is not effcicent due unknown reason. thus one of the possibility is that the cancer cell uses a similar mechanism to avoid our immune system like the trypanosoma brucei (a parasite) does using variant surface glycoprotein mechanism. that's is once the antibody produced for antigent 1, antigent 2 is expressed on the cancer cell surface and antigent 1 is no longer expressed thus a new antibody is required to eliminate the cancer cell and so on. all cancers express rather strange antigent (which some can be the… [cont.]
Answered by lippy19850528 - Sun Oct 29 18:45:19 2006
