Glycosaminoglycans (GAGs) or
mucopolysaccharides are long unbranched
polysaccharidePolysaccharides are polymeric carbohydrate structures, formed of repeating units joined together by glycosidic bonds. These structures are often linear, but may contain various degrees of branching. Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit...
s consisting of a repeating
disaccharideA disaccharide is the carbohydrate formed when two monosaccharides undergo a condensation reaction which involves the elimination of a small molecule, such as water, from the functional groups only...
unit.
Protein cores made in the rough
endoplasmic reticulumThe endoplasmic reticulum is an eukaryotic organelle that forms an interconnected network of tubules, vesicles, and cisternae within cells. The lacey membranes of the endoplasmic reticulum were first seen by Keith R. Porter, Albert Claude, and Ernest F...
are posttranslationally modified by glycosyltransferases in the
Golgi apparatusThe Golgi apparatus is an organelle found in most eukaryotic cells...
, where GAG disaccharides are added to protein cores to yield proteoglycans; the exception is
hyaluronanHyaluronan is an anionic, non-sulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues...
, which is uniquely synthesized without a protein core and is "spun out" by enzymes at cell surfaces directly into the extracellular space.
This family of carbohydrates is essential or important for life.
GAGs form an important component of
connective tissueConnective tissue is a form of fibrous tissue.. It is one of the four types of tissue in traditional classifications ....
s.
Glycosaminoglycans (GAGs) or
mucopolysaccharides are long unbranched
polysaccharidePolysaccharides are polymeric carbohydrate structures, formed of repeating units joined together by glycosidic bonds. These structures are often linear, but may contain various degrees of branching. Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit...
s consisting of a repeating
disaccharideA disaccharide is the carbohydrate formed when two monosaccharides undergo a condensation reaction which involves the elimination of a small molecule, such as water, from the functional groups only...
unit.
Production
Protein cores made in the rough
endoplasmic reticulumThe endoplasmic reticulum is an eukaryotic organelle that forms an interconnected network of tubules, vesicles, and cisternae within cells. The lacey membranes of the endoplasmic reticulum were first seen by Keith R. Porter, Albert Claude, and Ernest F...
are posttranslationally modified by glycosyltransferases in the
Golgi apparatusThe Golgi apparatus is an organelle found in most eukaryotic cells...
, where GAG disaccharides are added to protein cores to yield proteoglycans; the exception is
hyaluronanHyaluronan is an anionic, non-sulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues...
, which is uniquely synthesized without a protein core and is "spun out" by enzymes at cell surfaces directly into the extracellular space.
Function
This family of carbohydrates is essential or important for life.
GAGs form an important component of
connective tissueConnective tissue is a form of fibrous tissue.. It is one of the four types of tissue in traditional classifications ....
s. GAG chains may be
covalently linkedA covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or between atoms and other covalent bonds...
to a
proteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
to form
proteoglycanProteoglycans are glycoproteins that are heavily glycosylated. They have a core protein with one or more covalently attached glycosaminoglycan chain. The chains are long, linear carbohydrate polymers that are negatively charged under physiological conditions, due to the occurrence of sulfate and...
s.
Water sticks to GAGs, this is where the resistance to pressure comes from. The density of sugar molecules and the net negative charges attract salts. Ex: Na+, and after the sodium binds it attracts water molecules. Water does not compress, unlike gas.
Some examples of glycosaminoglycan uses in nature include
heparinHeparin, a highly-sulfated glycosaminoglycan, is widely used as an injectable anticoagulant, and has the highest negative charge density of any known biological molecule. It can also be used to form an inner anticoagulant surface on various experimental and medical devices such as test tubes and...
as an
anticoagulantAn anticoagulant is a substance that prevents coagulation; that is, it stops blood from clotting. A group of pharmaceuticals called anticoagulants can be used in vivo as a medication for thrombotic disorders...
, hyaluronate as a component in the
synovial fluidSynovial fluid is a thick, stringy fluid found in the cavities of synovial joints. With its sperm-like consistency , synovial fluid reduces friction between the articular cartilage and other tissues in joints to lubricate and cushion them during movement.-Overview:The inner membrane of synovial...
lubricant in body joints, and
chondroitinsChondroitin sulfate is a sulfated glycosaminoglycan composed of a chain of alternating sugars . It is usually found attached to proteins as part of a proteoglycan. A chondroitin chain can have over 100 individual sugars, each of which can be sulfated in variable positions and quantities...
which can be found in connective tissues,
cartilageCartilage is a stiff yet flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
and
tendonA tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fascia as they are all made of collagen except that ligaments join one bone to another bone, and fascia connect muscles to other...
s.
Classification
Members of the glycosaminoglycan family vary in the type of hexosamine, hexose or hexuronic acid unit they contain (e.g.
glucuronic acidGlucuronic acid is a carboxylic acid. Its structure is similar to that of glucose. However, glucuronic acid's sixth carbon is oxidized to a carboxylic acid...
,
iduronic acidL-Iduronic acid is the major uronic acid component of the glycosaminoglycans dermatan sulfate and heparin. It is also present in heparan sulfate although here in a minor amount relative to its carbon-5 epimer glucuronic acid....
,
galactoseGalactose is a type of sugar which is less sweet than glucose. It is considered a nutritive sweetener because it has food energy. Its name comes from the Ancient Greek word for milk, γάλακτος ....
,
galactosamineGalactosamine is a hexosamine derived from galactose with the molecular formula C6H13NO5. This amino sugar is a constituent of some glycoprotein hormones such as follicle-stimulating hormone and luteinizing hormone...
,
glucosamineGlucosamine is an amino sugar and a prominent precursor in the biochemical synthesis of glycosylated proteins and lipids. Glucosamine is part of the structure of the polysaccharides chitosan and chitin, which compose the exoskeletons of crustaceans and other arthropods, cell walls in fungi and...
).
They also vary in the geometry of the glycosidic linkage.
Examples of GAGs include:
| Name |
Hexuronic acid / Hexose |
Hexosamine |
Linkage geometry between predominant monomeric units |
Unique features
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| Chondroitin sulfateChondroitin sulfate is a sulfated glycosaminoglycan composed of a chain of alternating sugars . It is usually found attached to proteins as part of a proteoglycan. A chondroitin chain can have over 100 individual sugars, each of which can be sulfated in variable positions and quantities...
|
GlcUA or GlcUA(2S) |
GalNAc or GalNAc(4S) or GalNAc(6S) or GalNAc(4S,6S) |
-4GlcUAβ1-3GalNAcβ1- |
|
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| Dermatan sulfateDermatan sulfate is a glycosaminoglycan found mostly in skin, but also in blood vessels, heart valves, tendons, and lungs....
GlcUA or IdoUA or IdoUA(2S) |
GalNAc or GalNAc(4S) or GalNAc(6S) or GalNAc(4S,6S) |
-4IdoUAβ1-3GalNAcβ1- |
iduronic acidL-Iduronic acid is the major uronic acid component of the glycosaminoglycans dermatan sulfate and heparin. It is also present in heparan sulfate although here in a minor amount relative to its carbon-5 epimer glucuronic acid....
, although some hexuronic acid monosaccharides may be glucuronic acidGlucuronic acid is a carboxylic acid. Its structure is similar to that of glucose. However, glucuronic acid's sixth carbon is oxidized to a carboxylic acid...
.
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| Keratan sulfateKeratan sulfate , also called keratosulfate, is any of several sulfated glycosaminoglycans that have been found especially in the cornea, cartilage, and bone. It is also synthesized in the central nervous system where it participates both in development and in the glial scar formation following an...
|
Gal or Gal(6S) |
GlcNAc or GlcNAc(6S) |
-3Gal(6S)β1-4GlcNAc(6S)β1- |
fucosylatedFucose is a hexose deoxy sugar with the chemical formula C 6H 12O 5. 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...
.
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| HeparinHeparin, a highly-sulfated glycosaminoglycan, is widely used as an injectable anticoagulant, and has the highest negative charge density of any known biological molecule. It can also be used to form an inner anticoagulant surface on various experimental and medical devices such as test tubes and...
|
GlcUA or IdoUA(2S) |
GlcNAc or GlcNS or GlcNAc(6S) or GlcNS(6S) |
-4IdoUA(2S)α1-4GlcNS(6S)α1- |
|
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| Heparan sulfateHeparan sulfate is a linear polysaccharide found in all animal tissues. It occurs as a proteoglycan in which two or three HS chains are attached in close proximity to cell surface or extracellular matrix proteins...
GlcUA or IdoUA or IdoUA(2S) |
GlcNAc or GlcNS or GlcNAc(6S) or GlcNS(6S) |
-4GlcUAβ1-4GlcNAcα1- |
|
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| HyaluronanHyaluronan is an anionic, non-sulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues...
GlcUA |
GlcNAc |
-4GlcUAβ1-3GlcNAcβ1- |
The only GAG that is exclusively non-sulfated |
Abbreviations
- GlcUA = β-D-glucuronic acid
Glucuronic acid is a carboxylic acid. Its structure is similar to that of glucose. However, glucuronic acid's sixth carbon is oxidized to a carboxylic acid...
- GlcUA(2S) = 2-O-sulfo-β-D-glucuronic acid
- IdoUA = α-L-iduronic acid
L-Iduronic acid is the major uronic acid component of the glycosaminoglycans dermatan sulfate and heparin. It is also present in heparan sulfate although here in a minor amount relative to its carbon-5 epimer glucuronic acid....
- IdoUA(2S) = 2-O-sulfo-α-L-iduronic acid
- Gal = β-D-galactose
Galactose is a type of sugar which is less sweet than glucose. It is considered a nutritive sweetener because it has food energy. Its name comes from the Ancient Greek word for milk, γάλακτος ....
- Gal(6S) = 6-O-sulfo-β-D-galactose
- GalNAc = β-D-N-acetylgalactosamine
N-Acetylgalactosamine , is an amino sugar derivative of galactose.-Function:In humans it is the terminal carbohydrate forming the antigen of blood group A....
- GalNAc(4S) = β-D-N-acetylgalactosamine-4-O-sulfate
- GalNAc(6S) = β-D-N-acetylgalactosamine-6-O-sulfate
- GalNAc(4S,6S) = β-D-N-acetylgalactosamine-4-O, 6-O-sulfate
- GlcNAc = α-D-N-acetylglucosamine
N-Acetylglucosamine is a monosaccharide derivative of glucose. It is an amide between glucosamine and acetic acid...
- GlcNS = α-D-N-sulfoglucosamine
- GlcNS(6S) = α-D-N-sulfoglucosamine-6-O-sulfate
External links
- Proteoglycans and Glycosaminoglycans at Lancaster University
Lancaster University, officially The University of Lancaster, is a British university in Lancaster, Lancashire, England. Lancaster is the 7th highest ranking research institution in the United Kingdom according to the last Research Assessment Exercise. The University has an annual income of £149...
- Illustration at scientificpsychic.com
- King M. 2005. Glycosaminoglycans. Indiana University School of Medicine
The Indiana University School of Medicine is the medical school of Indiana University. It is part of the Indiana University-Purdue University Indianapolis campus in Indianapolis, Indiana. Established in 1903, the school had an initial class of 25 students...
Accessed December 31, 2006.