Glycosaminoglycans (GAGs) or mucopolysaccharides are long, linear
polysaccharide
Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wa ...
s consisting of repeating
disaccharide
A disaccharide (also called a double sugar or ''biose'') is the sugar formed when two monosaccharides are joined by glycosidic linkage. Like monosaccharides, disaccharides are simple sugars soluble in water. Three common examples are sucrose, lact ...
units (i.e. two-sugar units). The repeating two-sugar unit consists of a
uronic sugar and an
amino sugar
In organic chemistry, an amino sugar (or more technically a 2-amino-2-deoxysugar) is a sugar molecule in which a hydroxyl group has been replaced with an amine group. More than 60 amino sugars are known, with one of the most abundant being ''N'' ...
, except in the case of the
sulfated
Sulfation is the chemical reaction that entails the addition of SO3 group. In principle, many sulfations would involve reactions of sulfur trioxide (SO3). In practice, most sulfations are effected less directly. Regardless of the mechanism, the ...
glycosaminoglycan
keratan
Keratan sulfate (KS), also called keratosulfate, is any of several sulfated glycosaminoglycans (structural carbohydrates) that have been found especially in the cornea, cartilage, and bone. It is also synthesized in the central nervous system w ...
, where, in place of the uronic sugar there is a
galactose
Galactose (, '' galacto-'' + '' -ose'', "milk sugar"), sometimes abbreviated Gal, is a monosaccharide sugar that is about as sweet as glucose, and about 65% as sweet as sucrose. It is an aldohexose and a C-4 epimer of glucose. A galactose molec ...
unit. GAGs are found in vertebrates, invertebrates and bacteria.
Because GAGs are highly
polar molecule
In chemistry, polarity is a separation of electric charge leading to a molecule or its chemical groups having an electric dipole moment, with a negatively charged end and a positively charged end.
Polar molecules must contain one or more polar ...
s and attract water; the body uses them as lubricants or shock absorbers.
Mucopolysaccharidoses
Mucopolysaccharidoses are a group of metabolic disorders caused by the absence or malfunctioning of lysosomal enzymes needed to break down molecules called glycosaminoglycans (GAGs). These long chains of sugar carbohydrates occur within the ce ...
are a group of
metabolic disorder
A metabolic disorder is a disorder that negatively alters the body's processing and distribution of macronutrients, such as proteins, fats, and carbohydrates. Metabolic disorders can happen when abnormal chemical reactions in the body alter the ...
s in which abnormal accumulations of glycosaminoglycans occur due to enzyme deficiencies.
Production
Glycosaminoglycans vary greatly in molecular mass, disaccharide structure, and sulfation. This is because GAG synthesis is not template driven, as are proteins or nucleic acids, but constantly altered by processing enzymes.
GAGs are classified into four groups, based on their core disaccharide structures.
Heparin
Heparin, also known as unfractionated heparin (UFH), is a medication and naturally occurring glycosaminoglycan. Since heparins depend on the activity of antithrombin, they are considered anticoagulants. Specifically it is also used in the treatm ...
/heparan sulfate (HSGAGs) and
chondroitin sulfate
Chondroitin sulfate is a sulfated glycosaminoglycan (GAG) composed of a chain of alternating sugars ( N-acetylgalactosamine and glucuronic acid). It is usually found attached to proteins as part of a proteoglycan. A chondroitin chain can have ove ...
/
dermatan sulfate
Dermatan sulfate is a glycosaminoglycan (formerly called a mucopolysaccharide) found mostly in skin, but also in blood vessels, heart valves, tendons, and lungs.
It is also referred to as chondroitin sulfate B, although it is no longer classifie ...
(CSGAGs) are synthesized in the
Golgi apparatus
The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, it packages proteins into membrane-bound vesicles ins ...
, where
protein cores made in the
rough endoplasmic reticulum
The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( ...
are post-translationally modified via
O-linked glycosylation
''O''-linked glycosylation is the attachment of a sugar molecule to the oxygen atom of serine (Ser) or threonine (Thr) residues in a protein. ''O''-glycosylation is a post-translational modification that occurs after the protein has been synthesise ...
by
glycosyltransferase
Glycosyltransferases (GTFs, Gtfs) are enzymes ( EC 2.4) that establish natural glycosidic linkages. They catalyze the transfer of saccharide moieties from an activated nucleotide sugar (also known as the "glycosyl donor") to a nucleophilic glycos ...
s ,forming
proteoglycan
Proteoglycans are proteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan (GAG) chain(s). The point of attachment is a serine (Ser) residue to whic ...
s.
Keratan sulfate
Keratan sulfate (KS), also called keratosulfate, is any of several sulfated glycosaminoglycans (structural carbohydrates) that have been found especially in the cornea, cartilage, and bone. It is also synthesized in the central nervous system w ...
may modify core proteins through
N-linked glycosylation
''N''-linked glycosylation, is the attachment of an oligosaccharide, a carbohydrate consisting of several sugar molecules, sometimes also referred to as glycan, to a nitrogen atom (the amide nitrogen of an asparagine (Asn) residue of a protein), ...
or O-linked glycosylation of the proteoglycan. The fourth class of GAG,
hyaluronic acid
Hyaluronic acid (; abbreviated HA; conjugate base hyaluronate), also called hyaluronan, is an anionic, nonsulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues. It is unique among glycosaminoglycans ...
, is synthesized by integral membrane synthases, which immediately secrete the dynamically elongated disaccharide chain.
HSGAG and CSGAG
HSGAG and CSGAG modified proteoglycans first begin with a consensus Ser-Gly/Ala-X-Gly motif in the core protein. Construction of a tetrasaccharide linker that consists of -GlcAβ1–3Galβ1–3Galβ1–4Xylβ1-O-(Ser)-, where
xylosyltransferase
Xylosyltransferase are transferase enzymes which act upon xylose and are classified under EC 2.4.2.
More specifically, they can refer to:
* Dolichyl-phosphate D-xylosyltransferase
* Dolichyl-xylosyl-phosphate-protein xylosyltransferase
* Flavon ...
, β4-galactosyl transferase (GalTI),β3-galactosyl transferase (GalT-II), and β3-GlcA transferase (GlcAT-I) transfer the four monosaccharides, begins synthesis of the GAG modified protein. The first modification of the tetrasaccharide linker determines whether the HSGAGs or CSGAGs will be added. Addition of a GlcNAc promotes the addition of HSGAGs while addition of GalNAc to the tetrasaccharide linker promotes CSGAG development.
GlcNAcT-I transfers GlcNAc to the tetrasaccahride linker, which is distinct from glycosyltransferase GlcNAcT-II, the enzyme that is utilized to build HSGAGs. EXTL2 and EXTL3, two genes in the EXT tumor suppressor family, have been shown to have GlcNAcT-I activity. Conversely, GalNAc is transferred to the linker by the enzyme GalNAcT to initiate synthesis of CSGAGs, an enzyme which may or may not have distinct activity compared to the GalNAc transferase activity of chondroitin synthase.
With regard to HSGAGs, a multimeric enzyme encoded by EXT1 and EXT2 of the EXT family of genes, transfers both GlcNAc and GlcA for HSGAG chain elongation. While elongating, the HSGAG is dynamically modified, first by N-deacetylase, N-sulfotransferase (
NDST1
Bifunctional heparan sulfate N-deacetylase/N-sulfotransferase 1 is an enzyme. In humans, it is encoded by the ''NDST1'' gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of ...
), which is a bifunctional enzyme that cleaves the N-acetyl group from GlcNAc and subsequently sulfates the N-position. Next, C-5 uronyl epimerase coverts d-GlcA to l-IdoA followed by 2-''O'' sulfation of the uronic acid sugar by 2-''O'' sulfotransferase (
Heparan sulfate 2-O-sulfotransferase
Heparan sulfate 2-O-sulfotransferase is a sulfotransferase enzyme. Heparan sulfate (HS) is a long unbranched polysaccharide found covalently attached to various proteins at the cell surface and in the extracellular matrix, where it acts as a co-re ...
). Finally, the 6-''O'' and 3-''O'' positions of GlcNAc moities are sulfated by 6-''O'' (
Heparan sulfate 6-O-sulfotransferase
Heparan sulfate 6-sulfotransferases catalyses the transfer of sulfate from adenosine 3'-phosphate, 5'-phosphosulfate to the 6th position of the N- sulfoglucosamine residue in heparan sulfate
Heparan sulfate (HS) is a linear polysaccharide foun ...
) and 3-O (3-OST) sulfotransferases.
Chondroitin sulfate and dermatan sulfate, which comprise CSGAGs, are differentiated from each other by the presence of GlcA and IdoA epimers respectively. Similar to the production of HSGAGs, C-5 uronyl epimerase converts d-GlcA to l-IdoA to synthesize dermatan sulfate. Three sulfation events of the CSGAG chains occur: 4-''O'' and/or 6-''O'' sulfation of GalNAc and 2-''O'' sulfation of uronic acid. Four isoforms of the 4-''O'' GalNAc sulfotransferases (C4ST-1, C4ST-2, C4ST-3, and D4ST-1) and three isoforms of the GalNAc 6-''O'' sulfotransferases (C6ST, C6ST-2, and GalNAc4S-6ST) are responsible for the sulfation of GalNAc.
Keratan sulfate types
Unlike HSGAGs and CSGAGs, the third class of GAGs, those belonging to keratan sulfate types, are driven towards biosynthesis through particular protein sequence motifs. For example, in the cornea and cartilage, the keratan sulfate domain of
aggrecan
Aggrecan (ACAN), also known as cartilage-specific proteoglycan core protein (CSPCP) or chondroitin sulfate proteoglycan 1, is a protein that in humans is encoded by the ''ACAN'' gene. This gene is a member of the lectican (chondroitin sulfate prote ...
consists of a series of tandemly repeated hexapeptides with a consensus sequence of E(E/L)PFPS.
Additionally, for three other keratan sulfated proteoglycans,
lumican
Lumican, also known as LUM, is an extracellular matrix protein that, in humans, is encoded by the ''LUM'' gene on chromosome 12.
Structure
Lumican is a proteoglycan Class II member of the small leucine-rich proteoglycan (SLRP) family that incl ...
,
keratocan
Keratocan (KTN) also known as keratan sulfate proteoglycan keratocan, is a protein that in humans is encoded by the ''KERA'' gene.
Keratan sulfate proteoglycans (KSPGs) are members of the small leucine-rich proteoglycan (SLRP) family. KSPGs, par ...
, and mimecan (
OGN), the consensus sequence NX(T/S) along with protein secondary structure was determined to be involved in ''N''-linked oligosaccharide extension with keratan sulfate.
Keratan sulfate elongation begins at the nonreducing ends of three linkage oligosaccharides, which define the three classes of keratan sulfate. Keratan sulfate I (KSI) is ''N'' -linked via a high mannose type precursor oligosaccharide. Keratan sulfate II (KSII) and keratan sulfate III (KSIII) are ''O''-linked, with KSII linkages identical to that of
mucin
Mucins () are a family of high molecular weight, heavily glycosylated proteins (glycoconjugates) produced by epithelial tissues in most animals. Mucins' key characteristic is their ability to form gels; therefore they are a key component in most ...
core structure, and KSIII linked to a 2-''O'' mannose. Elongation of the keratan sulfate polymer occurs through the glycosyltransferase addition of Gal and GlcNAc. Galactose addition occurs primarily through the β-1,4-galactosyltransferase
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
(β4Gal-T1) while the enzymes responsible for β-3-Nacetylglucosamine have not been clearly identified. Finally, sulfation of the polymer occurs at the 6-position of both sugar residues. The enzyme KS-Gal6ST (
CHST1
Carbohydrate sulfotransferase 1 is an enzyme that in humans is encoded by the ''CHST1'' gene
In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generatio ...
) transfers sulfate groups to galactose while N-acetylglucosaminyl-6-sulfotransferase (GlcNAc6ST) (
CHST2
Carbohydrate sulfotransferase 2 is an enzyme that in humans is encoded by the ''CHST2'' gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation ...
) transfers sulfate groups to terminal GlcNAc in keratan sulfate.
Hyaluronic acid class
The fourth class of GAG,
hyaluronic acid
Hyaluronic acid (; abbreviated HA; conjugate base hyaluronate), also called hyaluronan, is an anionic, nonsulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues. It is unique among glycosaminoglycans ...
(HA), is not sulfated and is synthesized by three transmembrane synthase proteins
HAS1
Hyaluronan synthase 1 is an enzyme that in humans is encoded by the ''HAS1'' gene.
Structure
Hyaluronan or hyaluronic acid (HA) is a high molecular weight unbranched polysaccharide synthesized by a wide variety of organisms from bacteria to ma ...
,
HAS2
Hyaluronan synthase 2 is an enzyme that in humans is encoded by the ''HAS2'' gene.
Hyaluronan or hyaluronic acid is a high molecular weight unbranched polysaccharide synthesized by a wide variety of organisms from bacteria to mammals, and is a co ...
, and
HAS3
Hyaluronan synthase 3 is an enzyme that in humans is encoded by the ''HAS3'' gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''b ...
. HA, a linear polysaccharide, is composed of repeating disaccharide units of →4)GlcAβ(1→3)GlcNAcβ(1→ and has a very high molecular mass,
ranging
Length measurement, distance measurement, or range measurement (ranging) refers to the many ways in which length, distance, or range can be measured. The most commonly used approaches are the rulers, followed by transit-time methods and the int ...
from 10
5 to 10
7 Da. Each HAS enzyme is capable of transglycosylation when supplied with UDP-GlcA and UDP-GlcNAc. HAS2 is responsible for very large hyaluronic acid polymers, while smaller sizes of HA are synthesized by HAS1 and HAS3. While each HAS isoform catalyzes the same biosynthetic reaction, each HAS isoform is independently active. HAS isoforms have also been shown to have differing ''K''
m values for UDP-GlcA and UDPGlcNAc. It is believed that through differences in enzyme activity and expression, the wide spectrum of biological functions mediated by HA can be regulated, such as its involvement with
neural stem cell
Neural stem cells (NSCs) are self-renewing, multipotent cells that firstly generate the radial glial progenitor cells that generate the neurons and glia of the nervous system of all animals during embryonic development. Some neural progenitor ste ...
regulation in the
subgranular zone
The subgranular zone (SGZ) is a brain region in the hippocampus where adult neurogenesis occurs. The other major site of adult neurogenesis is the subventricular zone (SVZ) in the brain.
Structure
The subgranular zone is a narrow layer of cell ...
of the brain.
Function
;CSGAGs: Endogenous heparin is localized and stored in secretory granules of
mast cell
A mast cell (also known as a mastocyte or a labrocyte) is a resident cell of connective tissue that contains many granules rich in histamine and heparin. Specifically, it is a type of granulocyte derived from the myeloid stem cell that is a par ...
s.
Histamine
Histamine is an organic nitrogenous compound involved in local immune responses, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Since histamine was discovered in ...
that is present within the granules is protonated (H
2A
2+) at pH within granules (5.2–6.0), thus it is believed that heparin, which is highly negatively charged, functions to electrostatically retain and store histamine.
In the clinic, heparin is administered as an anticoagulant and is also the first line choice for thromboembolic diseases. Heparan sulfate (HS) has numerous biological activities and functions, including cell adhesion, regulation of cell growth and proliferation, developmental processes, cell surface binding of lipoprotein lipase and other proteins, angiogenesis, viral invasion, and tumor metastasis.
CSGAGs interact with heparin binding proteins, specifically dermatan sulfate interactions with fibroblast growth factor FGF-2 and FGF-7 have been implicated in cellular proliferation and wound repair
while interactions with hepatic growth factor/scatter factor (HGF/SF) activate the HGF/SF signaling pathway (
c-Met
c-Met, also called tyrosine-protein kinase Met or hepatocyte growth factor receptor (HGFR), is a protein that in humans is encoded by the ''MET'' gene. The protein possesses tyrosine kinase activity. The primary single chain precursor protein is ...
) through its receptor. CASGAGs are important in providing support and adhesiveness in bone, skin, and cartilage. Other biological functions for which CSGAGs are known to play critical functions in include inhibition of axonal growth and regeneration in CNS development, roles in brain development, neuritogenic activity, and pathogen infection.
;Keratan sulfates:One of the main functions of the third class of GAGs, keratan sulfates, is the maintenance of tissue hydration.
Keratan sulfates are in the bone, cartilage, and the cornea of the eye.
Within the normal cornea, dermatan sulfate is fully hydrated whereas keratan sulfate is only partially hydrated suggesting that keratan sulfate may behave as a dynamically controlled buffer for hydration.
In disease states such as
macular corneal dystrophy
Macular corneal dystrophy, also known as Fehr corneal dystrophy named for German ophthalmologist Oskar Fehr (1871-1959), is a rare pathological condition affecting the stroma of cornea. The first signs are usually noticed in the first decade of li ...
, in which GAGs levels such as KS are altered, loss of hydration within the corneal stroma is believed to be the cause of corneal haze, thus supporting the long-held hypothesis that corneal transparency is a dependent on proper levels of keratan sulfate. Keratan sulfate GAGs are found in many other tissues besides the cornea, where they are known to regulate
macrophage
Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer cel ...
adhesion, form barriers to
neurite
A neurite or neuronal process refers to any projection from the cell body of a neuron. This projection can be either an axon or a dendrite. The term is frequently used when speaking of immature or developing neurons, especially of cells in culture ...
growth, regulate
embryo implantation in the endometrial uterine lining during menstrual cycles, and affect the motility of corneal endothelial cells.
In summary, KS plays an anti-adhesive role, which suggests very important functions of KS in cell motility and attachment as well as other potential biological processes.
Dermatan sulfates
Dermatan sulfates function in the skin, tendons, blood vessels, and heart valves.
;Hyaluronic acid:
Hyaluronic acid
Hyaluronic acid (; abbreviated HA; conjugate base hyaluronate), also called hyaluronan, is an anionic, nonsulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues. It is unique among glycosaminoglycans ...
is a major component of
synovial tissues and
fluid
In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...
, as well as the
ground substance Ground substance is an amorphous gel-like substance in the extracellular space that contains all components of the extracellular matrix (ECM) except for fibrous materials such as collagen and elastin. Ground substance is active in the development, m ...
of other connective tissues. Hyaluronic acid binds cells together, lubricates joints, and helps maintain the shape of the eyeballs.
:The
viscoelasticity
In materials science and continuum mechanics, viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like water, resist shear flow and strain linearly wi ...
of hyaluronic acid make it ideal for lubricating joints and surfaces that move along each other, such as cartilage. A solution of hyaluronic acid under low shear stress has a much higher viscosity than while under high shear stress.
Hyaluronidase
Hyaluronidases are a family of enzymes that catalyse the degradation of hyaluronic acid (HA). Karl Meyer classified these enzymes in 1971, into three distinct groups, a scheme based on the enzyme reaction products. The three main types of hyal ...
, an enzyme produced by white blood cells, sperms cells, and some bacteria, breaks apart the hyaluronic acid, causing the solution to become more liquid.
:''In vivo'', hyaluronic acid forms randomly kinked coils that entangle to form a hyaluronan network, slowing diffusion and forming a diffusion barrier that regulates transport of substances between cells. For example, hyaluronan helps partition plasma proteins between vascular and extravascular spaces, which affects solubility of macromolecules in the interstitium, changes chemical equilibria, and stabilizes the structure of collagen fibers.
:Other functions include matrix interactions with hyaluronan binding proteins such as hyaluronectin, glial hyaluronan binding protein, brain enriched hyaluronan binding protein,
collagen VI Collagen VI (ColVI) is a type of collagen primarily associated with the extracellular matrix of skeletal muscle. ColVI maintains regularity in muscle function and stabilizes the cell membrane. It is synthesized by a complex, multistep pathway that l ...
,
TSG-6
Tumor necrosis factor-inducible gene 6 protein also known as TNF-stimulated gene 6 protein or TSG-6 is a protein that in humans is encoded by the ''TNFAIP6'' (tumor necrosis factor, alpha-induced protein 6) gene.
Structure and function
TSG-6 is ...
, and
inter-alpha-trypsin inhibitor Inter-alpha-trypsin inhibitors (IαI) are plasma proteins consisting of three of four heavy chains selected from the group ITIH1, ITIH2, ITIH3, ITIH4 and one light chain selected from the group Alpha-1-microglobulin/bikunin precursor, AMBP or SPINT2 ...
. Cell surface interactions involving hyaluronan are its well-known coupling with
CD44
The CD44 antigen is a cell-surface glycoprotein involved in cell–cell interactions, cell adhesion and migration. In humans, the CD44 antigen is encoded by the ''CD44'' gene on chromosome 11. CD44 has been referred to as HCAM (homing cell adhesi ...
, which may be related to tumor progression, and also with RHAMM (
Hyaluronan-mediated motility receptor), which has been implicated in developmental processes, tumor metastasis, and pathological reparative processes. Fibroblasts, mesothelial cells, and certain types of stem cells surround themselves in a pericellular "coat", part of which is constructed from hyaluronan, in order to shield themselves from bacteria, red blood cells, or other matrix molecules. For example, with regards to stem cells, hyaluronan, along with chondroitin sulfate, helps to form the
stem cell niche. Stem cells are protected from the effects of growth factors by a shield of hyaluronan and minimally sulfated chondroitin sulfate. During progenitor division, the daughter cell moves outside of this pericellular shield where it can then be influenced by growth factors to differentiate even further.
Classification
Members of the glycosaminoglycan family vary in the type of hexosamine, hexose or hexuronic acid unit they contain (e.g.
glucuronic acid
Glucuronic acid (from Greek γλεῦκος "''wine, must''" and οὖρον "''urine''") is a uronic acid that was first isolated from urine (hence the name). It is found in many gums such as gum arabic (c. 18%), xanthan, and kombucha tea and ...
,
iduronic acid
-Iduronic acid (IUPAC abbr.: IdoA) is the major uronic acid component of the glycosaminoglycans (GAGs) dermatan sulfate, and heparin. It is also present in heparan sulfate, although here in a minor amount relative to its carbon-5 epimer glucuronic ...
,
galactose
Galactose (, '' galacto-'' + '' -ose'', "milk sugar"), sometimes abbreviated Gal, is a monosaccharide sugar that is about as sweet as glucose, and about 65% as sweet as sucrose. It is an aldohexose and a C-4 epimer of glucose. A galactose molec ...
,
galactosamine
Galactosamine 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 (FSH) and luteinizing hormone (LH).
Precursors such a ...
,
glucosamine
Glucosamine (C6H13NO5) is an amino sugar and a prominent precursor in the biochemical synthesis of glycosylated proteins and lipids. Glucosamine is part of the structure of two polysaccharides, chitosan and chitin. Glucosamine is one of the most ...
).
They also vary in the geometry of the
glycosidic linkage
A glycosidic bond or glycosidic linkage is a type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate.
A glycosidic bond is formed between the hemiacetal or hemiketal grou ...
.
Examples of GAGs include:
Abbreviations
* GlcUA = ''β''-D-
glucuronic acid
Glucuronic acid (from Greek γλεῦκος "''wine, must''" and οὖρον "''urine''") is a uronic acid that was first isolated from urine (hence the name). It is found in many gums such as gum arabic (c. 18%), xanthan, and kombucha tea and ...
* GlcUA(2S) = 2-O-sulfo-''β''-D-glucuronic acid
* IdoUA = ''α''-L-
iduronic acid
-Iduronic acid (IUPAC abbr.: IdoA) is the major uronic acid component of the glycosaminoglycans (GAGs) dermatan sulfate, and heparin. It is also present in heparan sulfate, although here in a minor amount relative to its carbon-5 epimer glucuronic ...
* IdoUA(2S) = 2-O-sulfo-''α''-L-iduronic acid
* Gal = ''β''-D-
galactose
Galactose (, '' galacto-'' + '' -ose'', "milk sugar"), sometimes abbreviated Gal, is a monosaccharide sugar that is about as sweet as glucose, and about 65% as sweet as sucrose. It is an aldohexose and a C-4 epimer of glucose. A galactose molec ...
* Gal(6S) = 6-O-sulfo-''β''-D-galactose
* GalNAc = ''β''-D-
N-acetylgalactosamine
* 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 (GlcNAc) is an amide derivative of the monosaccharide glucose. It is a secondary amide between glucosamine and acetic acid. It is significant in several biological systems.
It is part of a biopolymer in the bacterial ...
* GlcNS = ''α''-D-N-sulfoglucosamine
* GlcNS(6S) = ''α''-D-N-sulfoglucosamine-6-O-sulfate
See also
*
Lipopolysaccharide
Lipopolysaccharides (LPS) are large molecules consisting of a lipid and a polysaccharide that are bacterial toxins. They are composed of an O-antigen, an outer core, and an inner core all joined by a covalent bond, and are found in the outer m ...
References
External links
* King M. 2005.
Glycosaminoglycans Indiana University School of Medicine
The Indiana University School of Medicine (IUSM) is a major multi-campus medical school in the state of Indiana. There are nine campuses throughout the state; the principal research and medical center is located on the Indiana University–Purdu ...
Accessed December 31, 2006.
*
MRI evaluation of glycosaminoglycan loss (dGEMRIC evaluation)
{{Authority control