Harvey's Garden

Extracellular matrix

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Extracellular matrix fibers (connective tissue fibers)

Collagen fibers, Reticular fibers, and Elastic fibers

Collagen

Structure

  • A collagen molecule is a protein with a repeating amino acid sequence (Gly-X-Y)n.
    • The first amino acid of this triplet is glycine (collagen is comprised of ⅓ glycine).
    • Position X: most commonly proline (also common: lysine, hydroxylysine)
    • Position Y: most commonly hydroxyproline (also common: hydroxylysine, lysine)

Types

And scar tissue (late stages of wound healing, e.g. post-MI) See Osteogenesis imperfecta

Tip

  • Compare with ligaments, which are made of elastin.
  • Ligaments attach bone to bone, and tendons attach muscle to bone.
  • Connect presence of elastin with Marfan syndrome
    • FBN1 can disrupt the normal regulation of TGF-β → Tall stature
    • Skin → Skin hyperextensibility
    • Large arteries → aortic dilation, aneurysms, or dissection
    • Elastic ligaments → Joint hypermobility
    • Lung → Increased risk of spontaneous pneumothorax

Deficient in vascular type of Ehlers-Danlos syndrome (threE D).

See Goodpasture syndrome

Glycosaminoglycans (GAGs)

  • Definition: a family of unbranched polysaccharide chains of repeating disaccharide units with multiple negative charges that constitute a large volume fraction of the ECM
  • Structure: polymer of repeating disaccharide units
  • Four main groups
    • Hyaluronic acid
    • Chondroitin sulfate and dermatan sulfate
    • Heparan sulfate
    • Keratan sulfate
  • Function
    • Bind H2O in connective tissue due to its negative charges: act as a cushion
    • Component of proteoglycans

Proteoglycans

  • Definition: proteins with numerous covalently linked GAG side chains
  • Function
    • Bind H2O → shock absorption and a supportive function (e.g., in cartilage → resistance to compression of articular cartilage)
    • Formation of cell-cell junction or cell-matrix junction
    • Further signaling and regulatory functions (e.g., by binding signaling molecules)
  • Examples
    • Aggrecan: large proteoglycan found in cartilage as an aggregate with hyaluronic acid → shock absorption withstands compression
    • Decorin: small proteoglycan that binds collagen fibrils → regulates fibril assembly

Glycoproteins of the ECM

  • Definition: proteins with short carbohydrate side chains that contribute to the organization of the extracellular matrix by offering specific binding sites for cells and other matrix molecules
  • Examples
    • Fibronectin
      • Glycoprotein important for cell-matrix interactions
      • Function: binds to collagen and integrins and plays an important role in embryogenesis (regulates cell migration) and hemostasis (cross-linking of fibrin molecules with thrombocytes and fibroblasts)
    • Laminin
      • Major component and organizer of the basal lamina (besides type IV collagen)
      • Function: binds to collagens, integrins, and proteoglycans

Graph View

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