ECM

• The glyocalyx or cell coat

  • buffer before ECM
  • carbohydrate projections extending from integral membrane proteins in the membrane

  Roles

  • Mediate cell-cell and cell-substratum interactions,
  • mechanical protection
  • serves as a barrier
• Basement membrane (specialized ECM of epithelial cells)

  Extends further past plasma membrane than the cell coat and consists of secreted proteins

  Sends signals for:

  • survival
  • differentiation
  • orientation
• ECM helps cells form organized hollow balls, suggesting that the ECM has important roles in organization and cell-cell interactions
• 4 types of ECM proteins:

  • collagen
  • proteoglycans
  • fibronectin
  • laminins

  all interact with integrin, and thus must all have a RGD peptide
• Structure of collagen 1

  • triple helix of 3 alpha-helix chains
  • fibrous glycoprotein only present in ECM - very strong
  • produced by fibroblasts found in dermis of connective tissue
  • smooth muscle cells and epithelial cells
• The corneal stroma has uniform and alternate layers of collagen

  to provide strength and maintain transparency


  • Collagen provides the insoluble framework that determines many of the mechanical properties of the matrix.
  • Tissue properties can often be correlated with the 3D organization of its collagen (e.g., tendons, cornea).
• Collagens resist pulling forces and form a scaffold for proteoglycans, together providing ECMs strength and resistance
• Proteoglycans


  • bind huge numbers of cations, which bind a large number of water molecules to form a porous hydrated gel
  • This results in increased resistance to crushing or compression
  • seen in cartilage to help cushion mechanical forces
  • protein-polysaccharide, consisting of a core protein, carrying covalently attached glycosylaminoglycans (negative charge)
  • each polypeptide binds to numerous ECM components and cell surface receptors
• The interaction domains of the fibronectin molecule

  A fibronectin molecule consists of two similar polypeptides joined by a pair of disulfide bonds.

  • Each polypeptide is composed of a linear series of distinct modules
  • bind to numerous ECM components
  • bind to cell surface receptors
• Cells migrate on fibronectin coated glass and die if they move off the fibronectin. Therefore, not all ECM components may be necessary for survival, although the cell function would be inhibited
• Laminins

  • trimers organized into a cross-like shape
  • glycoproteins made of 3 different proteins linked by disulfide bonds
  • involved in migration, growth and differentiation (specialization)
  • Bind cell-surface receptors, other laminins, to proteoglycans and other BM proteins.
  • Laminin and collagen IV form separate but interconnected networks.
• Laminin role in embryogenesis

  • germ cells have to travel from one side of the embryo to the other and use highways of laminin to migrate
  • Role in development of neuronal outgrowth
  • Strengthen basement membrane