Glycosaminoglycans and
Proteoglycans
Dr. M. Jawad Hassan
Extracellular Macromolecules
macromolecule
glycosaminoglycans* (GAGs)
proteoglycans*
glycoproteins
fibrous proteins
Examples of functions:
mechanical support
cushioning
cell spacers
% carb.
100
90-95
2-30
1-2
lubrication
adhesives
selective filters
1 * mucopolysaccharides, mucoproteins, respectively
GAG structure

C
HO
HO
exist as:
– independent molecules
e.g., hyaluronate & heparin
– parts of larger structures
e.g., in proteoglycans

heteropolysaccharides
repeating structure:
disaccharide (AB)n
O–
O
H2C OH
HO
HO
A sugar
O
OH
OH
B sugar
O
OH
NH2
ABABAB…
– where A is usually 1 uronic acid (hexose with C6 as COO– )
– & B is 1 glycosamine (amino sugar) derivative

unbranched
– glycosidic linkage
– anomeric C of 1 unit linked to hydroxyl of adjacent unit
3
GAG structure: repeating units
GAG
A sugar
hyaluronate
B sugar
glucuronate
O–
O
C
O
*
O
H
N-acetyl glucosamine
O HO
O
OH 1,3
H2C OH
O
5
1,4
O
2
NH
H3C
O
4
GAG structure: repeating units
GAG
A sugar
hyaluronate
B sugar
glucuronate
O–
O
C
O
chondroitin sulfate
dermatan sulfate
heparan sulfate
heparin
keratan sulfate
*
O
H
4
N-acetyl glucosamine
O HO
O
OH 1,3
H2C OH
O
5
1,4
O
2
NH
H3C
O
glucuronate
N-Ac galactosamine 4-SO4
iduronate
"
glucuronate
glucosamine N-SO3, 6-SO4
iduronate 2-SO4
"
galactose
N-Ac glucosamine 6-SO4
*opposite configuration in iduronate
glucuronate/iduronate: epimers at C5
glucose/galactose: epimers at C4
Hyaluronate
5
mol wt: 106 – 107 (5000 – 50,000 monosaccharide units)
 very polar:
2 hydroxyls/unit 6 heteroatoms/unit
COO– every other unit
Display of HA
+
++
binds cations: Na , Ca

in motion
A
B
A
B
A
B
–
–
–
1
2
3
4
5
(glucuronate–N-acetyl glucosamine)3 (glcUA–glcNAc)3
6
6
Hyaluronate: structure & properties
extended structure (charge repulsion)
 hydrophilic: binds 10 –100 × wt in H2O
 additional, loosely associated H2O, so that volume
occupied ~1000 × weight
Display of HA with

glcUAs in CPK
–
–
–
1
(glcUA–glcNAc)3
2
3
4
5
glcUAs in space-filling form (CPK)
6
Hyaluronate
solutions viscous, gel–like,

compression-resistant
 occurrence: EC matrix,
esp. in developing tissue
healing wounds
synovial fluid
 functions: lubricant
shock absorber
flexible cement
attachment site
path for cell migration
 made by fibroblasts
 degraded by hyaluronidase
hyaluronidase
– bacterial hyaluronidase facilitates
spread of infection
7
Alberts et al. Fig. 19-37
Heparin
O
104
O SO3–
H2C
O 1,4
1,4
O
O
O
HO
O SO3–
H
C
mol wt ~
O
O–
 ~ 40 monosaccharide units
 made & released from mast cells in lungs & liver

–
HN SO3
O
heparin
cell
8
Heparin
O
104
O SO3–
H2C
O 1,4
1,4
O
O
O
HO
O SO3–
O
H
C
mol wt ~
O
O–
 ~ 40 monosaccharide units
 made & released from mast cells in lungs & liver
 also associated with luminal surface of endothelium
heparin
 anticoagulant

– forms complex with antithrombin III
– this complex binds to thrombin, inactivating it
– as a result, clot growth is limited
– fast-acting, making it therapeutically useful
8
–
HN SO3
cell
Extracellular Macromolecules
macromolecule
glycosaminoglycans* (GAGs)
proteoglycans*
glycoproteins
fibrous proteins
Examples of functions:
mechanical support
cushioning
cell spacers
% carb.
100
90-95
2-30
1-2
lubrication
adhesives
selective filters
* mucopolysaccharides, mucoproteins, respectively
Proteoglycans (PGs)
composed of as many as 200 GAG chains covalently
bonded to a core protein via serine side chains
 molecular weight range: 105 – 107
 GAG chains:
chondroitin sulfate, heparan sulfate,
dermatan sulfate, keratan sulfate

Examples

decorin
– many connective tissues
– binds type I collagen, TGF-

perlecan
– basal laminae
– structural & filtering function
aggrecan
 syndecan (slide 13)

9
GAG chains
core
protein
PG in basal lamina of renal glomerulus

adapted from
Alberts et al.,
3 ed., Fig. 19-56
network of
fibrous
proteins &
perlecan
PG forms
filter
entactin
perlecan
laminin
10
type IV collagen
Proteoglycans: aggrecan
~100 GAG chains/molecule
 ~100 monosaccharides/GAG chain
 each "bristle" = 1 GAG chain
 each GAG chain is either chondroitin sulfate
or keratan sulfate
 GAG chains linked to ser side chains of core protein

core
protein
11
GAG chains
An aggregate of aggrecans & hyaluronan
major GAG–PG
in cartilage
 link proteins bind
non-covalently
 with bound H2O,
disperses shocks,
compressive force
 ~ cell size
 adhesion proteins
hyalurlink to collagen &onan
cells
keratan
 degraded by
sulfate
chondroitin
12 sulfatase, etc

 1m 
core protein
link proteins
chondroitin
sulfate
Alberts et al. Fig. 19-41
Repeating units of some common glycosaminoglycans of extracellular matrix
linear polymers composed of
repeating disaccharide units
Glucoronic acid
N-Acetylglucosamine
Proteoglycans:
syndecan
cell-surface PG
 core protein domains

– intracellular
– transmembrane
– extracellular
5 GAGs attached

GAG chains
outside
functions
– interactions
 cell-cell
 cell-matrix
– growth factor receptor
13
inside
core
protein
Lehninger et al.
Fig. 9-22
Proteoglycans are glycosaminoglycans-containing macromolecules
of the cell surface and extracellular matrix
Proteoglycan structure
GAG synthesis & breakdown
O–
O
C

synthesis
HO
HO
O
–UDP
OH
– activated precursors: UDP–monosaccharide derivatives
e.g., UDP–glucuronate
– residues added one at a time in Golgi complex
– sulfate moieties
O

14
degradation
O O
–
O S
P
O O–
O
O
adenine
O
OH
P O
O O–
–
– lysosomes
– specific glycosidases & sulfatases
– mucopolysaccharidoses
 genetic disorders
 accumulation of GAG due to absence of a specific
glycosidase or sulfatase
GAG synthesis & breakdown

Synthesis of amino sugars

GlcNAc and GalNac (fructose 6 phosphate)

NANA (N-acetyle mannosamin and
phophoenol pyruvate)

CMP-NANA synthetase for activation.

Synthesis of acidic sugars
– Glucoronic acid and L-Iduronic acid
– Diet, lysosomal degradation via uronic acid pathway
– Active form is UDP-glucoronic acid
Synthesis of carbohydrate chain and addition of sulphates
Xylosyltransferase
sulphotransferases
PAPS is sulphar donor

Degradation
– Acid hydrolases
– Phagocytosis
– Lysosomal degradation (endoglycosidases)
Properties of proteoglycans

Glycosylated proteins which have covalently attached highly anionic
glycosaminoglycans (GAGs)

Highly hydrated gels (due to charged sugars). Resist compression
-Sulfated glycosaminoglycans (disaccharides) are negatively charged: bind cations and
water

Core proteins link to hyaluronic acid (MW: 3 x 106)

Number of disaccharides typically found in each glycosaminoglycan chain
Heparin/Heparan sulfate (n = 15-30)
Keratan sulfate (n = 20-40)
Chondroitin sulfate (n < 250)
Hyaluron (n < 50,000)

Can be in the ECM and on the surface of cells
E.g. Syndecan (integral membrane protein with Heparan sulfate) is present on
the surface of epithelial cells
MUCOPOLYSACCHARIDOSES (MPS)
Rare inborn errors in the degradation of glycosaminoglycans result
in a series of diseases called mucopolysaccharidoses. They are
characterized by mental retardation and/or structural defects.
MPS Type I
Hurler’s syndrome results from a deficiency of alpha-L-iduronidase.
Heparan sulfate and dermatan sulfate accumulate. There is growth
and mental retardation with characteristic facial changes.
MPS Type II
Hunters syndrome is similar to Hurler’s syndrome but the enzyme
deficiency is for iduronate sulfatase and the inheritance is Xlinked.
MPS Type III
Sanfilipo’s syndrome is caused by a deficiency of one of four
enzymes of which three are hydrolases and one is an Nacetyltransferase. There is severe mental retardation but only mild
structural features.
Other MPS Types are
IV, VI and VII. There is no MPS Type V.
MPS I (Hurler
Syndrome)
A deficiency of Liduronidase leads to
mental retardation and
structural changes due
to
accumulation
of
dermatan sulfate and
heparan sulfate
MPS
II
(Hunter
Syndrome)
X-linked disease due to a
deficiency of iduronate
sulfatase
MPS
III
Syndrome)
(Sanfilippo
Deficiency in one of four
degradative enzymes leads
to
severe
mental
retardation
but
little
structural change
MPS IV (Morquio Syndrome)
Deficiency of a galactose-6-sulfatase or a betagalactosidase leads to accumulation of keratan sulfate
with normal intelligence but severe deformity
THANK YOU