GAGS

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GLYCOSAMINO GLYCANS

• M.Prasad Naidu
• MSc Medical Biochemistry,
• Ph.D.Research Scholar

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GLYCOSAMINO GLYCANS

• They differ form each other in a number of the
  following properties.
• Chain length.
• Amino Acid composition.
• Uronic Acid composition.
• Linkages between these components.
• Presence or absence of sulfate groups.
• The attachment of sulfate to sugar molecule.
• The nature of core protein linked to GAG.
• The tissue and sub. Cellular distribution of GAG.

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FUNCTIONS OF GAG

1. Structural component of extra cellular matrix.
2. Contribute to the turgor of various tissues.
3. Acts as sieves in EC matrix
4. Facilitate cell migration,acts as shock
   absorber at joints,(HA)
5. Maintenance of compressibility of
   cartilage(HACS)
6. Have a structural role in sclera in corneal
   transparency (KS1,DS)

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FUNCTIONS OF GAG CONT-----

• 7. Acts as anticoagulant (HA)
• 8. Determines the charge selectiveness of renal
  glomerulus.(HS)
• 9. Formation of cell membrane and synaptic
  vesicles (HS)

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Glycosaminoglycans / GAGS or Mucopolysaccharides

• Are large complex of ve charged (carboxy
  sulfate groups) heteropolysaccharide chain
  generally associated with a small amount of
  protein - proteoglycan.
• Special ability to bind large amount of water
  producing gel like matrix, that forms the bodies
  ground substance.
• Unbranched, long repeating diasaccharide Contains
  uronic acid amino sugars.

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• Amino sugar D-Glucosamine or D-Galactosamine.
• Uronic acid D-Glucuronic acid or L-Iduronic
  acid.

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Classification
GAGS
Sulphate free
Sulphate containing
Chondrotin Sulphate Dermatan sulphate keratan
sulphate Heparin Heparan Sulphate
Hyaluronic acid

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1. Chondroitin sulfate

• Contains D-Glucoronic acid Galactosamine.
• Most abundant GAG in body.

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• Widely distributed in bone, cartilage tendons.
• Function
• In cartilage, it binds collagen hold fibers in
  a tight strong network.
• Role in Compressibility of cartilage in weight
  bearing along with Hyaluronic acid.
• 2 types of chondroitin sulfate
• Sulphated at C 4 or C 6 group.

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2. Hyaluronic acid

• Contains D-Glucoronic acid Glucosamine.
• It is sulphate free GAG.
• It is sulphate free GAG.

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• Ground substance of synovial fluid of joints,
  vitreous humor of eyes and connective tissues,
  tendon.
• Hyaluronidase is an enzyme that breaks ß-1 4
  linkages.
• Present in high concentration in testes, seminal
  fluid, in certain snake and insect venoms.

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Functions of Hyaluronic acid

• Serves as a lubricant and shock absorbant in
  joints.
• Determines charge selectiveness of renal
  glomerulus.
• Acts as seives in extracelluar matrix.
• Permits cell migration during morphogenesis
  wound repair.
• Hyaluronidase enzyme of semen degrades the gel
  around ovum allows effective penetration of
  sperm into ovum.

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3. Dermatan sulfate

• Contains L-iduronic acid Glucosamine

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• Present in skin, cardiac valves tendon.
• Function
• Present in sclera of eye where it has important
  function in maintaining overall shape of eye.

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4. Heparin

• Contains D-Glucuronic acid Glucosamine
• it is the only intracellular GAG.

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• It is an anticoagulant (prevents blood clotting )
  
• Found in granules of mast cells that line the
  arteries of lung, liver, kidney, spleen.
• Strongly acidic due to presence of more sulphate
  group.
• Heparin helps in the release of the enzyme
  lipoprotein lipase.
• Helps to clear the lipidemia after fatty meal
  also called clearing factor.

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5. Heparan sulfate

• Same as heparin except some amino groups carry
  acetyl group of Sulphate groups are
  smaller.
• It is extracellular GAG .
• Present in basement membrane as a ubiquitous
  component of cell surface.

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6. Keratan sulfate

• contains D-Galactose Glucosamine
• Only GAG with no uronic acid.

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• Found in cornea tendon.
• 2 types
• Keratan sulfate ? cornea
• Keratan sulfate ?? skeletal muscle
• Function
• Maintains the corneal transparency.

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Proteoglycan
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Heteropolysaccharide

• Agar
• Contains galactose , glucose other sugars.
• Cannot be digested by bacteria.
• So used as supporting agent to culture bacterial
  colonies.
• Also as support medium of immuno diffusion
  immuno-electrophoresis.
• Agarose
• galactose 3,6 anhydro galactose units
• Used as matrix for electrophoresis.