Glycoprotein

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Glycoprotein

Not to be confused with peptidoglycan
Peptidoglycan

Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of bacteria, forming the cell wall....
or proteoglycan
Proteoglycan

File:PBB Protein ACAN image.jpgProteoglycans represent a special class of glycoproteins that are heavily glycosylation. They consist of a core protein with one or more covalent bond attached glycosaminoglycan chain....
.

Glycoproteins are proteins that contain oligosaccharide

Oligosaccharide

An oligosaccharide is a saccharide polymer containing a small number of component sugars, also known as simple sugars. The name derived from the Greek oligos, meaning "a few"....
chains (glycans

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....
) covalently attached to their polypeptide

Peptide

Peptides are short polymers formed from the linking, in a defined order, of a-amino acids. The link between one amino acid residue and the next is known as an amide chemical bond or a peptide bond....
side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification

Posttranslational modification

Posttranslational modification is the chemistry 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

Glycosylation is the enzymatic process that links saccharides to produce glycans, either free or attached to proteins and lipids. This enzymatic process produces one of four fundamental components of all cells and also provides a co-translational and post-translational modification mechanism that modulates the structure and function of membr...
. 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.

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Encyclopedia

Oligosaccharide

Glycans

Peptide

Posttranslational modification

Glycosylation

Cytosol

The cytosol or intracellular fluid is the liquid found inside cell . 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....
, but their functions and the pathways producing these modifications in this compartment are less well-understood.

N-glycosylation and O-glycosylation

There are two types of glycosylation:

In N-glycosylation
Glycosylation

Glycosylation is the enzymatic process that links saccharides to produce glycans, either free or attached to proteins and lipids. This enzymatic process produces one of four fundamental components of all cells and also provides a co-translational and post-translational modification mechanism that modulates the structure and function of membr...
(see on the right), the addition of sugar chains can happen at the amide nitrogen on the side chain of the asparagine
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....
.
In O-glycosylation
Glycosylation

Glycosylation is the enzymatic process that links saccharides to produce glycans, either free or attached to proteins and lipids. This enzymatic process produces one of four fundamental components of all cells and also provides a co-translational and post-translational modification mechanism that modulates the structure and function of membr...
, the addition of sugar chains can happen on the hydroxyl
Hydroxyl

Hydroxyl in chemistry stands for a molecule consisting of an oxygen atom and a hydrogen atom connected by a covalent bond. The neutral form is a hydroxyl Radical and the hydroxyl anion is called a hydroxide....
oxygen
Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
on the side chain of hydroxylysine
Hydroxylysine

5-Hydroxylysine is an amino acid with the molecular formula C6H14N2O3. It is a hydroxy derivative of lysine....
, hydroxyproline
Hydroxyproline

4-Hydroxyproline, or hydroxyproline , is an uncommon amino acid, abbreviated as HYP, e.g., in Protein Data Bank....
, serine
Serine

Serine is an organic compound with the chemical formula hydrogenoxygen2carbonCHCH2OH....
, or threonine
Threonine

Threonine is an a-amino acid with the chemical formula HO2CCHCHCH3. Its codons are ACU, ACA, ACC, and ACG. This essential amino acid is classified as Chemical polarity....
.

Monosaccharides

Monosaccharides commonly found in eukaryotic glycoproteins include:

The principal sugars found in human glycoproteins
Sugar	Type	Abbreviation
ß-D-Glucose Glucose Glucose , a monosaccharide also known as grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology....	Hexose Hexose In organic chemistry, a hexose is a monosaccharide with six carbon atoms, having the chemical formula C6H12O6. Hexoses are classified by functional group, with aldohexoses having an aldehyde at position 1, and ketohexoses having a ketone at position 2....	Glc
ß-D-Galactose Galactose Galactose is a type of Carbohydrate which is less sweetness than glucose. It is considered a nutritive sweetener because it has food energy.Galactan is a polymer of the sugar galactose....	Hexose	Gal
ß-D-Mannose Mannose Mannose is a sugar monomer of the hexose series of carbohydrates....	Hexose	Man
a-L-Fucose Fucose Fucose is a hexose deoxy sugar with the chemical formula C6H12O5. It is found on N-linked glycans on the mammalian, insect and plant cell surface, and is the fundamental sub-unit of the fucoidan polysaccharide....	Deoxyhexose Deoxy sugar Deoxy sugars are sugars that have had a hydroxyl group replaced with a hydrogen.Examples include:* Deoxyribose * Fucose* Rhamnose...	Fuc
N-Acetylgalactosamine N-Acetylgalactosamine N-Acetylgalactosamine is a monosaccharide derivative of galactose....	Aminohexose	GalNAc
N-Acetylglucosamine N-Acetylglucosamine N-Acetylglucosamine is a monosaccharide derivative of glucose. Chemically it is an amide between glucosamine and acetic acid. It has a molecular formula of carbon8hydrogen15nitrogenoxygen6, a molar mass of 221.21 g/mol, and it is significant in several biological systems....	Aminohexose	GlcNAc
N-Acetylneuraminic acid N-Acetylneuraminic acid N-Acetylneuraminic acid is the predominant sialic acid found in mammalian cells.This negatively charged residue is found in complex glycans on mucins and glycoproteins found at the cell membrane....	Aminononulosonic acid Neuraminic acid Neuraminic acid is a 9-carbon monosaccharide, a derivative of a ketononose. Neuraminic acid may be visualized as the product of an aldol condensation product of pyruvic acid and D-mannosamine .... (Sialic acid 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.... )	NeuNAc
Xylose Xylose Xylose, or wood sugar, is an aldopentose — a monosaccharide containing five carbon atoms and including an aldehyde functional group. It has chemical formula 5105....	Pentose Pentose A pentose is a monosaccharide with five carbon atoms.They either have an aldehyde functional group in position 1 , or a ketone functional group in position 2 ....	Xyl

The sugar group(s) can assist in protein folding

Protein folding

Protein folding is the physical process by which a polypeptide folds into its characteristic and functional protein structure.Each protein begins as a polypeptide, translated from a sequence of mRNA as a linear chain of amino acids....
or improve proteins' stability.

Examples

One example of glycoproteins found in the body is mucin

Mucin

Mucins are a family of high molecular weight, heavily glycosylation proteins produced by many epithelial tissues in vertebrates. Although some mucins are cell membrane-bound due to the presence of a hydrophobic membrane-spanning domain that favors retention in the plasma membrane, most mucins are secretion onto mucosae or secreted to become...
s, 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

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 cell

White blood cells , or leukocytes , are cell of the immune system defending the body against both infectious disease and foreign materials....
recognition, especially in mammal

Mammal

Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young....
s. Examples of glycoproteins in the immune system

Immune system

An immune system is a collection of biological processes within an organism that protects against disease by identifying and killing pathogens and tumour cells....
are:

molecules such as antibodies
Antibody

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 bacterium and viruses....
(immunoglobulins), which interact directly with antigen
Antigen

An antigen is a substance that prompts the generation of antibodies and can cause an immune response. The word originated from the notion that they can stimulate antibody generation....
s
molecules of the major histocompatibility complex
Major histocompatibility complex

The major histocompatibility complex is a large genome 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, autoimmunity, and reproduction success....
(or MHC), which are expressed on the surface of cells and interact with T cell
T cell

T cells 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 ....
s as part of the adaptive immune response.

Other examples of glycoproteins include:

glycoprotein IIb/IIIa
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 coagulation#Platelet activation....
, an integrin found on platelets
Platelet

Platelets, or Thrombocyte, are small, irregularly shaped anuclear cells, 2-4?m in diameter, which are derived from fragmentation of precursor megakaryocytes....
that is required for normal platelet aggregation and adherence to the endothelium
Endothelium

The endothelium is the thin layer of cell that line the interior surface of blood vessels, forming an interface between circulating blood in the lumen and the rest of the vessel wall....
.
components of the zona pellucida
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....
, which surrounds the oocyte
Oocyte

An oocyte, ovocyte, or rarely ocyte, is a female gametocyte or germ cell involved in biological reproduction. In other words, it is an immature ovum, or ovum cell....
, and is important for sperm
Sperm

The term sperm is derived from the Greek word sperma and refers to the male reproductive Cell . In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell....
-egg interaction.
structural glycoproteins, which occur in connective tissue
Connective tissue

Connective tissue is a form of fibrous biological tissue.It is one of the four types of tissue in traditional classifications .Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% of the total protein content....
. These help bind together the fibers, cells, and ground substance of connective tissue
Connective tissue

Connective tissue is a form of fibrous biological tissue.It is one of the four types of tissue in traditional classifications .Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% of the total protein content....
. They may also help components of the tissue bind to inorganic substances, such as calcium
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 grey alkaline earth metal, and is the fifth most abundant element by mass in the earth's Crust ....
in bone
Bone

Bones are rigid organ that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red blood cell and white blood cells and store minerals....
.
Glycoprotein-41 (gp41
Gp41

gp41 is a glycoprotein non-covalent bond-bound to gp120, and provides the second step by which viral entry the cell. It is originally buried within the virus envelope, but, when gp120 binds to a CD4 receptor, gp120 changes its Conformational isomerism, causing gp41 to become exposed, where it can assist in fusion with the host cell....
) and glycoprotein-120 (gp120
Gp120

gp120 is a glycoprotein exposed on the surface of the HIV structure and genome. The 120 in its name comes from its molecular weight of 120 Dalton ....
) are HIV viral coat proteins.

Soluble glycoproteins often show a high viscosity

Viscosity

Viscosity is a measure of the Drag of a fluid which is being deformed by either shear stress or extensional stress. In everyday terms , viscosity is "thickness"....
, for example, in egg white

Egg white

File:Chicken egg01 monovular.jpgEgg 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 ....
and blood plasma

Blood plasma

Blood plasma is the liquid component of blood, in which the blood cells are suspended. It makes up about 55% of total blood volume. It is composed of mostly water , and contains dissolved proteins, glucose, clotting factors, mineral ions, Hormone and carbon dioxide ....
.

Hormones

Hormone

Hormones are chemicals released by cells that affect cells in other parts of the body. Only a small amount of hormone is required to alter cell metabolism....
s that are glycoproteins include:

Follicle-stimulating hormone
Follicle-stimulating hormone

Follicle-stimulating hormone is a hormone synthesized and secreted by gonadotropes in the anterior pituitary gland. FSH regulates the development, growth, pubertal maturation, and reproductive processes of the human body....
Luteinizing hormone
Luteinizing hormone

Luteinizing hormone is a hormone produced by the anterior pituitary gland.* In the female, an acute rise of LH ? the LH surge ? triggers ovulation....
Thyroid-stimulating hormone
Thyroid-stimulating hormone

Thyroid-stimulating hormone is a peptide hormone synthesized and secreted by thyrotrope cells in the anterior pituitary gland which regulates the endocrine function of the thyroid gland....
Human chorionic gonadotropin
Human chorionic gonadotropin

Human chorionic gonadotropin is a glycoprotein hormone produced in pregnancy that is made by the the developing embryo soon after Conception and later by the syncytiotrophoblast ....
Alpha-fetoprotein
Alpha-fetoprotein

Alpha-fetoprotein is a protein which in humans is encoded by the AFP gene.This gene encodes alpha-fetoprotein, a major plasma protein produced by the yolk sac and the liver during fetal life....
Erythropoietin (EPO)
Erythropoietin

Erythropoietin, or its alternative erythropoetin or EPO, is a glycoprotein hormone that controls erythropoiesis, or red blood cell production....

Functions

Some functions served by glycoproteins
Function	Glycoproteins
Structural molecule	Collagen Collagen Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content.... s
Lubricant and protective agent	Mucin Mucin Mucins are a family of high molecular weight, heavily glycosylation proteins produced by many epithelial tissues in vertebrates. Although some mucins are cell membrane-bound due to the presence of a hydrophobic membrane-spanning domain that favors retention in the plasma membrane, most mucins are secretion onto mucosae or secreted to become... s
Transport molecule	Transferrin Transferrin Transferrin is a blood plasma protein for iron ion delivery that, in humans, is encoded by the TF gene. Transferrin is a glycoprotein, which binds iron very tightly but reversibly.... , ceruloplasmin Ceruloplasmin Ceruloplasmin is officially known as ferroxidase or iron:oxygen oxidoreductase. It is the major copper-carrying protein in the blood, and in addition plays a role in iron metabolism....
Immunologic molecule	Immunoglobins Antibody 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 bacterium and viruses.... , histocompatibility Histocompatibility Histocompatibility is the property of having the same, or mostly the same, alleles of a set of genes called the major histocompatibility complex.... antigens
Hormone	Chorionoic gonadotropin Human chorionic gonadotropin Human chorionic gonadotropin is a glycoprotein hormone produced in pregnancy that is made by the the developing embryo soon after Conception and later by the syncytiotrophoblast .... , thyroid-stimulating hormone (TSH)
Enzyme	Various, eg, alkaline phosphatase Phosphatase A phosphatase is an enzyme that removes a phosphate group from its Substrate by Hydrolysis phosphoric acid monoesters into a phosphate ion and a molecule with a free hydroxyl group ....
Cell attachment-recognition site	Various proteins involved in cell-cell (eg, sperm Sperm The term sperm is derived from the Greek word sperma and refers to the male reproductive Cell . In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell.... -oocyte Oocyte An oocyte, ovocyte, or rarely ocyte, is a female gametocyte or germ cell involved in biological reproduction. In other words, it is an immature ovum, or ovum cell.... ), virus-cell, bacterium-cell, and hormone cell interactions
Antifreeze Antifreeze Antifreeze is a cryoprotectant used in internal combustion engines, and for many other heat transfer applications, such as HVAC chillers and solar water heaters....	Certain plasma proteins of coldwater fish
Interact with specific carbohydrates	Lectin Lectin Lectins are sugar-binding proteins which are highly specific for their sugar moieties. They typically play a role in biological recognition phenomena involving cells and proteins.... s, selectin Selectin Selectins are a family of cell adhesion molecules . All selectins are single-chain transmembrane glycoproteins that share similar properties to C-type lectins due to a related amino terminus and calcium-dependent binding.... s (cell adhesion lectins), antibodies
Receptor Receptor Receptor may refer to:*Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse...	Various proteins involved in hormone and drug action
Affect folding of certain proteins	Calnexin Calnexin Calnexin is a 90kDa integral protein of the endoplasmic reticulum . It consists of a large N-terminal calcium-Binding Lumen protein domain, a single transmembrane helix and a short , acidic cytoplasmic tail.... , calreticulin Calreticulin Calreticulin is a multifunctional protein that binds calcium ions , rendering it inactive. The Ca2+ is bound with low Chemical affinity, but high capacity, and can be released on a signal ....
Regulation of development	Notch Notch signaling The Notch signaling pathway is a highly conserved cell signaling system present in most multicellular organisms. Notch is present in all metazoans, and vertebrates possess four different notch receptors, referred to as NOTCH1, NOTCH2, Notch 3, and NOTCH4.... and its analogs, key proteins in development
Hemostasis Hemostasis Hemostasis is a complex process which causes the bleeding process to stop. Most time this includes the changing of blood from a fluid to a solid state.... (and thrombosis Thrombosis Thrombosis is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel is injured, the body uses platelets and fibrin to form a blood clot, because the first step in repairing it is to prevent loss of blood.... )	Specific glycoproteins on the surface membranes of platelet Platelet Platelets, or Thrombocyte, are small, irregularly shaped anuclear cells, 2-4?m in diameter, which are derived from fragmentation of precursor megakaryocytes.... s

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 Electrophoresis Electrophoresis is the best-known electrokinetic phenomena. It was discovered by Reuss in 1807. He observed that clay particles dispersed in water migrate under influence of an applied electric field.... separation.
Incubation of cultured cells with glycoproteins as radioactive decay Radioactive decay Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting ionizing particles and radiation. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, called the daughter nuclide.... bands	Leads to detection of a radioactive sugar after electrophoretic separation.
Treatment with appropriate endo- Endoglycosidase An Endoglycosidase is an enzyme that releases oligosaccharides from glycoproteins or glycolipids. Or it merely cleaves polysacharride chains between residues that are not the terminal residue, although releasing oligosaccharides from conjugated protein and lipid molecules is more common.... or exoglycosidase Exoglycosidase A exoglycosidase is a glycoside hydrolase enzyme which breaks the glycosidic bonds at the terminal residue.... or phospholipase Phospholipase A phospholipase is an enzyme that hydrolyzes phospholipids into fatty acids and other lipophilic substances. There are four major classes, termed A, B, C and D distinguished by what type of reaction they catalyze:... s	Resultant shifts in electrophoretic migration help distinguish among proteins with N-glycan, O-glycan, or GPI linkages and also between high mannose Mannose Mannose is a sugar monomer of the hexose series of carbohydrates.... and complex N-glycans.
Agarose-lectin Lectin Lectins are sugar-binding proteins which are highly specific for their sugar moieties. They typically play a role in biological recognition phenomena involving cells and proteins.... column chromatography Column chromatography Column chromatography in chemistry is a method used to purify individual chemical compounds from mixtures of compounds. It is often used for preparative applications on scales from micrograms up to kilograms....	To purify glycoproteins or glycopeptides that bind the particular lectin used.
Compositional analysis following acid hydrolysis Hydrolysis Hydrolysis is a chemical reaction during which one or more water are split into hydrogen and hydroxide ions which may go on to participate in further reactions....	Identifies sugars that the glycoprotein contains and their stoichiometry.
Mass spectrometry Mass spectrometry Mass spectrometry is an analytical technique for the determination of the elemental composition of a sample or molecule. It is also used for elucidating the chemical structures of molecules, such as peptides and other chemical compounds....	Provides information on molecular mass Molecular mass The molecular mass of a chemical compound, frequently referred by the older term molecular weight and abbreviated as MW, is the mass of one molecule of that substance, relative to the unified atomic mass unit u .... , composition, sequence, and sometimes branching of a glycan chain.
NMR spectroscopy NMR spectroscopy 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....	To identify specific sugars, their sequence, linkages, and the anomeric nature of glycosidic chain.
Methylation Methylation Methylation in the chemical sciences denotes the attachment or substitution of a methyl on various Substrate . This term is commonly used in chemistry, biochemistry, soil science and the biological sciences.... (linkage) analysis	To determine linkage between sugars.
Amino acid Amino acid In chemistry, an amino acid is a molecule containing both amine and carboxyl functional groups. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula H2NCHRCOOH, where R is an organic substituent.... or cDNA Complementary DNA In genetics, complementary DNA is DNA synthesized from a mature mRNA template in a reaction catalyzed by the enzyme reverse transcriptase. cDNA is often used to clone eukaryote genes in prokaryotes.... sequencing	Determination of amino acid sequence.

External links

- Home Page for Learning Environmental Chemistry
SPECIAL WEB SUPPLEMENT Science 23 March 2001 Vol 291, Issue 5512, Pages 2263-2502

Glycoprotein

N-glycosylation and O-glycosylation

Monosaccharides

Examples

Hormones

Functions

Analysis

See also

External links