Not to be confused with peptidoglycan. Not to be confused with Glycoprotein. Peptidoglycan, also known as murein, is a Polymer consisting of sugars and amino
Glycoproteins are proteins that contain oligosaccharide chains (glycans) covalently attached to their polypeptide side-chains. An oligosaccharide is a Saccharide polymer containing a small number (typically three to ten of component sugars also known as Simple sugars. The term glycan refers to a Polysaccharide or Oligosaccharide. Peptides (from the Greek πεπτίδια, "small digestibles" are short Polymers formed from the linking in a defined order of α- Amino The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. Posttranslational modification (PTM is the chemical modification of a Protein after its translation. This process is known as glycosylation. Glycosylation is the enzymatic process that links Saccharides to produce glycans, either free or attached to Proteins and Lipids This enzymatic 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. An Integral Membrane Protein ( IMP) is a Protein Molecule (or assembly of proteins that is permanently attached to the Biological membrane.
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N-glycosylation and O-glycosylation
There are two types of glycosylation:
- In N-glycosylation (see on the right), the addition of sugar chains can happen at the amide nitrogen on the side chain of the asparagine. Glycosylation is the enzymatic process that links Saccharides to produce glycans, either free or attached to Proteins and Lipids This enzymatic Asparagine (abbreviated as Asn or N; Asx or B represent either asparagine or Aspartic acid) is one of the 20 most common natural
- In O-glycosylation, the addition of sugar chains can happen on the hydroxyl oxygen on the side chain of hydroxylysine, hydroxyproline, serine, or threonine. Glycosylation is the enzymatic process that links Saccharides to produce glycans, either free or attached to Proteins and Lipids This enzymatic 5-Hydroxylysine is an Amino acid with the molecular formula C6H14N2O3 4-Hydroxyproline, or hydroxyproline ( C 5 H 9 O 3 N) is an uncommon Amino acid, abbreviated as HYP Serine (abbreviated as Ser or S) is an Organic compound with the formula H[[oxygen O]]2 CCH NH sub>2CH2OH Threonine (abbreviated as Thr or T) is an α- Amino acid with the Chemical formula HO2CCH(NH2CH(OHCH3
Monosaccharides
Monosaccharides commonly found in eukaryotic glycoproteins include:[2]
| Sugar | Type | Abbreviation |
|---|---|---|
| Galactose | Hexose | Gal |
| Glucose | Hexose | Glc |
| Mannose | Hexose | Man |
| N-Acetylneuraminic acid | Sialic acid (nine C atoms) | NeuAc |
| Fucose | Deoxyhexose | Fuc |
| N-Acetylgalactosamine | Aminohexase | GalNAc |
| N-Acetylglucosamine | Aminohexase | GlaNac |
| Xylose | Pentose | Xyl |
The sugar group(s) can assist in protein folding or improve proteins' stability. Galactose (Gal (also called brain sugar) is a type of Sugar which is less sweet than Glucose. In Organic chemistry, a hexose is a Monosaccharide with six Carbon atoms having the Chemical formula C6H12O6 Glucose (Glc a Monosaccharide (or simple Sugar) also known as grape sugar, is an important Carbohydrate in Biology. Mannose is a Sugar Monomer of the Hexose series of Carbohydrates Metabolism Mannose enters the carbohydrate Metabolism N-Acetylneuraminic acid (Neu5Ac or NANA is the predominant Sialic acid. Sialic acid is a generic term for the N - or O -substituted derivatives of Neuraminic acid, a Monosaccharide with a nine- Carbon backbone Fucose is a Hexose Deoxy sugar with the Chemical formula C6H12O5 N-Acetylgalactosamine (also called GalNAc, 2-Acetamido-2-deoxy-D-galactopyranose or N-Acetyl-D-galactosamine) is a Monosaccharide derivative N-Acetylglucosamine ( N-Acetyl-D-Glucosamine, or GlcNAc, or NAG) is a Monosaccharide derivative of Glucose. Xylose or wood sugar is an Aldopentose &mdash a Monosaccharide containing five Carbon Atoms and including an Aldehyde Functional A pentose is a Monosaccharide with five Carbon Atoms They either have an Aldehyde Functional group in position 1 ( aldopentoses Protein folding is the physical process by which a Polypeptide folds into its characteristic and functional three-dimensional structure.
Examples
One example of glycoproteins found in the body is mucins, which are secreted in the mucus of the respiratory and digestive tracts. Mucins are a family of large heavily glycosylated Proteins ( Glycoconjugates. The sugars attached to mucins give them considerable water-holding capacity and also make them resistant to proteolysis by digestive enzymes. Proteolysis is the directed degradation ( digestion) of Proteins by cellular Enzymes called Proteases or by intramolecular digestion
Glycoproteins are important for white blood cell recognition, especially in mammals. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands 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. An immune system is a collection of mechanisms within an Organism that protects against Disease by identifying and killing Pathogens and Tumor Antibodies (also known as immunoglobulins, abbreviated Ig) are Gamma globulin Proteins that are found in Blood or other Bodily An antigen (from antibody-generating) or immunogen is a substance that prompts the generation of Antibodies and can cause an immune response The major histocompatibility complex ( MHC) is a large genomic region or Gene family found in most Vertebrates It is the most gene-dense region T cells belong to a group of White blood cells known as Lymphocytes, and play a central role in Cell-mediated immunity.
Other examples of glycoproteins include:
- components of the zona pellucida, which surrounds the oocyte, and is important for sperm-egg interaction. The zona pellucida (or zona striata in older texts is a Glycoprotein membrane surrounding the Plasma membrane of an Oocyte. An oocyte, ovocyte, or rarely ocyte, is a female Gametocyte or Germ cell involved in reproduction. The term sperm is derived from the Greek word (σπέρμα sperma (meaning "seed" and refers to the male reproductive cells.
- structural glycoproteins, which occur in connective tissue. Connective tissue is one of the four types of tissue in traditional classifications (the others being epithelial, Muscle, and Nervous tissue) These help bind together the fibers, cells, and ground substance of connective tissue. Connective tissue is one of the four types of tissue in traditional classifications (the others being epithelial, Muscle, and Nervous tissue) They may also help components of the tissue bind to inorganic substances, such as calcium in bone. Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 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
Soluble glycoproteins often show a high viscosity, for example, in egg white and blood plasma. Viscosity is a measure of the resistance of a Fluid which is being deformed by either Shear stress or Extensional stress. Albumen redirects here For other uses see Albumen (disambiguation. Blood plasma is the Liquid component of Blood, in which the Blood cells are suspended
Hormones
Hormones that are glycoproteins include:
- 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 | Chorionoic gonadotropin, 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[4][5]
| Method | Use |
|---|---|
| Periodic acid-Schiff stain | Detects glycoproteins as pink bands after electrophoretic separation. Hormones (from Greek ὁρμή - "impetus" are chemicals released by cells that affect cells in other parts of the body Follicle-stimulating hormone ( FSH) is a Hormone synthesized and secreted by Gonadotropes in the Anterior pituitary gland. Luteinizing hormone ( LH, also known as lutropin) is a Hormone produced by the Anterior pituitary gland. Thyroid-stimulating hormone (also known as TSH or thyrotropin) is a Peptide hormone synthesized and secreted by Thyrotrope cells in the Human chorionic gonadotropin ( hCG) is a Glycoprotein Hormone produced in Pregnancy that is made by the Embryo soon after conception Alpha-fetoprotein ( AFP) is a molecule produced in the developing Embryo Erythropoietin (ɨˌɹɪθɹoʊˈpɔɪɨtɨn /ɨˌɹɪθɹoʊˈpɔɪtən/ or /ɨˌɹiːθɹoʊ-/ or EPO is a Glycoprotein Hormone that controls Collagen is the main Protein of Connective tissue in Animals and the most abundant protein in Mammals making up about 50% of the whole-body protein Mucins are a family of large heavily glycosylated Proteins ( Glycoconjugates. Transferrin is a Blood plasma Protein for Iron Ion delivery Transferrin is a Glycoprotein, which binds iron very tightly but reversibly Ceruloplasmin (or caeruloplasmin) is officially known as ferroxidase or iron(IIoxygen oxidoreductase. Antibodies (also known as immunoglobulins, abbreviated Ig) are Gamma globulin Proteins that are found in Blood or other Bodily Histocompatibility is the property of having the same or mostly the same Alleles of a set of Genes called the Major histocompatibility complex. Human chorionic gonadotropin ( hCG) is a Glycoprotein Hormone produced in Pregnancy that is made by the Embryo soon after conception A phosphatase is an Enzyme that removes a Phosphate group from its Substrate by hydrolysing Phosphoric acid mono Esters into The term sperm is derived from the Greek word (σπέρμα sperma (meaning "seed" and refers to the male reproductive cells. An oocyte, ovocyte, or rarely ocyte, is a female Gametocyte or Germ cell involved in reproduction. Antifreeze is a Cryoprotectant used in Internal combustion engines and for many other heat transfer applications such as electronics cooling and Chillers Lectins are sugar-binding Proteins which are highly specific for their sugar Moieties. Selectins are a family of cell adhesion Molecules (or CAMs. All selectins are single-chain transmembrane Glycoproteins that share similar properties Calnexin (CNX is a 90kDa Integral protein of the Endoplasmic reticulum (ER Calreticulin is a multifunctional Protein that binds Ca2+ Ions (a Second messenger Molecule in Signal transduction Hemostasis (or Haemostasis refers to a process whereby bleeding is halted in most animals with a closed Circulatory system. Thrombosis is the formation of a blood Clot ( Thrombus) inside a Blood vessel, obstructing the flow of Blood through the Circulatory Platelets, or Thrombocytes, are small cytoplasmic bodies derived from cells They circulate in the Blood of Mammals and are involved Periodic acid-Schiff ( PAS) is a Staining method used in Histology and Pathology. Electrophoresis is the most well-known electrokinetic phenomenon. |
| Incubation of cultured cells with glycoproteins as radioactive decay bands | Leads to detection of a radioactive sugar after electrophoretic separation. Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. |
| 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. An Endoglycosidase is an Enzyme that releases Oligosaccharides from Glycoproteins or Glycolipids Or it merely cleaves polysacharride chains between A exoglycosidase is a Glycoside hydrolase enzyme which breaks the glycosidic bonds at the terminal residue A phospholipase is an enzyme that converts Phospholipids into Fatty acids and other Lipophilic substances Mannose is a Sugar Monomer of the Hexose series of Carbohydrates Metabolism Mannose enters the carbohydrate Metabolism |
| Agarose-lectin column chromatography | To purify glycoproteins or glycopeptides that bind the particular lectin used. Agar or agar agar is a Gelatinous substance derived from Seaweed. Lectins are sugar-binding Proteins which are highly specific for their sugar Moieties. Column chromatography in Chemistry is a method used to purify individual Chemical compounds from mixtures of compounds |
| Compositional analysis following acid hydrolysis | Identifies sugars that the glycoprotein contains and their stoichiometry. Hydrolysis is a Chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions which may go on to participate in further reactions |
| Mass spectrometry | Provides information on molecular mass, composition, sequence, and sometimes branching of a glycan chain. Mass spectrometry is an analytical technique that identifies the chemical composition of a compound or sample based on the Mass-to-charge ratio of charged particles The molecular mass (abbreviated m of a substance, more commonly referred to as molecular weight and abbreviated as MW, is the Mass of one |
| NMR spectroscopy | To identify specific sugars, their sequence, linkages, and the anomeric nature of glycosidic chain. Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is the name given to a technique which exploits the magnetic properties of certain nuclei |
| Methylation (linkage) analysis | To determine linkage between sugars. Methylation is a term used in the chemical sciences to denote the attachment or substitution of a methyl group on various substrates. |
| Amino acid or cDNA sequencing | Determination of amino acid sequence. In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this In Genetics, complementary DNA ( cDNA) is DNA synthesized from a mature MRNA template in a reaction catalyzed by the enzyme Reverse |
References
- ^ Ruddock & Molinari (2006) Journal of Cell Science 119, 4373-4380
- ^ Robert K. Murray, Daryl K. Granner & Victor W. Rodwell: "Harper's Illustrated Biochemistry 27th Ed. ", p. 526, McGraw-Hill, 2006
- ^ Ibid. , p. 524
- ^ Ibid. , p. 525
- ^ Anne Dell, Howard R Morris: "Glycoprotein structure determination by mass spectrometry", Science 291(5512), 2351-2356 (2001), Review
See also
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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