Section 11 Extracellular Macromolecules

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Section 11 Extracellular Macromolecules

• 2/7 Glycosaminoglycans proteoglycans
  glycoproteins mucins
• 2/10 Glycoprotein synthesis plasma proteins
• 2/14 Molecular immunology innate immunity
  inflammation
• 2/17 Molecular immunology
• adaptive (acquired) immunity
• 2/21 Fibrous proteins keratin, collagen and
  elastin

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Section 11 Extracellular Macromolecules

• 1. Glycosaminoglycans Proteoglycans
• GlycoproteinsMucins

2/7/06
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Extracellular Macromolecules

• macromolecule carb.
• glycosaminoglycans (GAGs) 100
• proteoglycans 90-95
• glycoproteins 2-30
• fibrous proteins 1-2
• Examples of functions
• mechanical support lubrication
• cushioning adhesives
• cell spacers selective filters

aka mucopolysaccharides, mucoproteins,
respectively
1
4
Extracellular matrix in tissues

• ground substance fibers
• macromolecules between cells
• ground substance molecules
• GAGs/proteoglycans (mostly carbohydrate)
• fibers fibrous proteins structural
  adhesive
• especially abundantin connective tissue

epithelial cells
adhesionmolecules
extra-cellularmatrix
basallamina
underlying cells
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Adapted from Hypercell
5
GAG structure
A sugar

• exist as
• independent molecules e.g., hyaluronate
  heparin
• parts of larger structures e.g., in
  proteoglycans
• heteropolysaccharides repeating structure
  disaccharide (AB)n 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

B sugar
3
6
GAG structure repeating units
4

• GAG A sugar B sugarhyaluronate glucur
  onate N-acetyl glucosamine

2
5
7
GAG structure repeating units
4

• GAG A sugar B sugarhyaluronate glucur
  onate N-acetyl glucosamine
• chondroitin sulfate glucuronate N-Ac
  galactosamine 4-SO4
• dermatan sulfate iduronate "
• heparan sulfate glucuronate glucosamine N-SO3,
  6-SO4
• heparin iduronate 2-SO4
  "
• keratan sulfate galactose N-Ac glucosamine 6-SO4
• opposite configuration in iduronate
  glucuronate/iduronate epimers at C5
  glucose/galactose epimers at C4

2
5
8
GAG structure repeating units

• GAG A sugar B sugarhyaluronate glucur
  onate N-acetyl glucosamine
• chondroitin sulfate glucuronate N-Ac
  galactosamine 4-SO4
• heparan sulfate " glucosamine N-SO3 6-SO4
• heparin iduronate 2-SO4
  "
• dermatan sulfate iduronate N-Ac galactosamine
  4-SO4
• keratan sulfate galactose N-Ac glucosamine 6-SO4
• opposite configuration in iduronate

2

5
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Hyaluronate (aka hyaluronan)
5

• mol wt 106 107 (5000 50,000 monosaccharide
  units)
• very polar 2 hydroxyls/unit 6
  heteroatoms/unit COO every other unit
• binds cations Na, Ca

Display of HA in motion
A B A B A B
hyastk2.gif



1
2
3
4
5
6
(glucuronateN-acetyl glucosamine)3
(glcUAglcNAc)3
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Hyaluronate structure properties
6

• 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
hyacpk2.gif



2
3
1
4
5
6
(glcUAglcNAc)3 glcUAs in space-filling
form (CPK)
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Hyaluronate

• solutions viscous, gellike, 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

Alberts et al. Fig. 19-37
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12
Heparin

• mol wt 104
• 40 monosaccharide units
• made released from mast cells in lungs liver

heparin
cell
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Heparin

• mol wt 104
• 40 monosaccharide units
• made released from mast cells in lungs liver
• also associated with luminal surface of
  endothelium
• 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

heparin
cell
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Extracellular Macromolecules

• macromolecule carb.
• glycosaminoglycans (GAGs) 100
• proteoglycans 90-95
• glycoproteins 2-30
• fibrous proteins 1-2
• Examples of functions
• mechanical support lubrication
• cushioning adhesives
• cell spacers selective filters

aka mucopolysaccharides, mucoproteins,
respectively
15
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-b
• perlecan
• basal laminae
• structural filtering function
• aggrecan
• syndecan (slide 13)

from Alberts et al. Fig. 19-57
AlbertsT 19-3Dcrn GAGchndSO4/drmSO4
GAG chains
core protein
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16
PG in basal lamina of renal glomerulus
adapted from Alberts et al., 3 ed., Fig. 19-56

• network offibrousproteins perlecanPG forms
  filter

entactin
perlecan
GAGheparan SO4
laminin
type IV collagen
10
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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

based onAlberts et al. Fig. 19-37 4ed. 19-40
core protein
GAG chains
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An aggregate of aggrecans hyaluronan
? 1?m ?

• major GAGPGin cartilage
• link proteins bind noncovalently
• with bound H2O,disperses shocks,compressive
  force
• cell size
• adhesion proteins link to collagen cells
• degraded by chondroitin sulfatase, etc

core protein
link proteins
hyalur-onan
keratansulfate
chondroitinsulfate
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Alberts et al. Fig. 19-41
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Proteoglycans syndecan

• cell-surface PG
• core protein domains
• intracellular
• transmembrane
• extracellular
• 5 GAGs attached
• functions
• interactions
• cell-cell
• cell-matrix
• growth factor receptor

GAG chains
outside
inside
core protein
Lehninger et al. Fig. 9-22
13
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GAG synthesis breakdown

• synthesis
• activated precursors UDPmonosaccharide
  derivatives e.g., UDPglucuronate
• residues added one at a time in Golgi complex
• sulfate moieties
• donor PAPS (active sulfate)
• degradation
• lysosomes
• specific glycosidases sulfatases
• mucopolysaccharidoses
• genetic disorders
• accumulation of GAG due to absence of a specific
  glycosidase or sulfatase

UDP

adenine



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Extracellular Macromolecules

• macromolecule carb.
• glycosaminoglycans (GAGs) 100
• proteoglycans 90-95
• glycoproteins 2-30
• fibrous proteins 1-2
• polypeptide with 1 or more oligosaccharide side
  chains

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Glycoproteins functions of glyco moieties

• increase proteins solubility hydrophilicity
  (sl 19)
• stabilize protein against
• denaturation
• proteolysis
• markers
• direct protein's destination
• organelle
• plasma membrane
• export (secretion)
• indicate protein's lifetime (sl 21)
• part of the protein's receptor recognition site
  (sl 23)
• signal factors such as hormones, cytokines
• cell-cell adhesion proteins

Glycosylation one kind of post-translational
modificationothers phosphorylation
carboxylation
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Glycoprotein structure
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• polypeptide with 1 or more oligosaccharide side
  chains
• oligosaccharide linked to polypeptide in two
  ways
• type linked to side chain of organelle where
  sugars
• are added to protein
• O-linked serine (ser), threonine (thr), Golgi
  complex lumen
• (O-glycoside) hydroxylysine (in collagen)
• N-linked asparagine (asn) rough ER lumen
• (N-glycoside)

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Glyco moiety structure

• oligosaccharide chain extends away from protein
  surface
• units mostly hexoses in pyranose (6-atom ring)
  form
• branched
• glycosidic links varied ? or ? 1,2 1,3 1,4
• terminal sugaroften sialate

2
asn
7
2
7
asn
18
Stryer 4ed., p. 463
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Mucins salivary glycoproteins

• mol wt 106
• 800 short (disaccharide) side chains
• terminal sugar is sialate
• anionic sugar
• at end of glyco chains of many glycoproteins
• very hydrophilic, extended structure

galNAc sialate

2
19
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Mucins modification aggregation

• sialidase (neuraminidase)
• catalyzes hydrolysis of sialates from mucins
• secreted by oral bacteria
• products
• less hydrophilic, less H2O-soluble, more
  folded, more aggregated
• part of the enamel pellicle dental plaque
  matrix

galNAc sialate
x H2O
sialidase
x
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Role of glyco moiety in controlling protein
lifetime

• many blood proteins have glyco chains with
  terminal sialate
• endothelial surface sialidases slowly remove
  sialates from these circulating proteins
• rate of sialate removal depends on protein's
  structure
• now-exposed galglcNAc residues bind to
  asialoglycoprotein receptor on liver cell surface
• protein is then endocytosed broken down

sialoglycoprotein siagalglcNAccore
sugarsprotein
asialoglycoprotein galglcNAccore
sugarsprotein
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Blood group types
Type O cell surface
galglcNAcgalglcprotein
fucose
Type A cell surface galNAcgalglcNAcgal
glcprotein
fucose
Type B cell surface
galgalglcNAcgalglcprotein
fucose

• A have enzyme to add galNAc to core sugars
  antibody to type B antigen
• B have enzyme to add gal to core sugars
  antibody to type A antigen
• O have neither enzyme
• AB have both enzymes (either galNAc or gal
  added to core sugars)

both antibodies
neither antibody
22
6-deoxygalactose
or lipid
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Glyco moiety-binding proteins lectins

• contain sites that bind specific glyco structures
• e.g., asialoglycoprotein receptor described on sl
  21
• important in intercell adhesion (i.e., lectins
  are CAMs cell adhesion molecules)
• selectinsplasmamembranelectins
  thatmediatecell-cellrecognition adhesion

Lehninger et al. Fig. 7-37
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Next lecture2. Glycoproteinscontinued