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Structural Proteins

Extra Cellular Matrix & Cell-Matrix Interactions Q

  1. Function:
    1. Sequesters H2O: turgor.     
    2. Sequesters minerals: rigidity (SK. Tissues)
    3. Reservoir for GF                
    4. Substrate for cells to adhere, migrate, proliferate
  2. Classified as Three groups:
    1. Fibrous structural proteins - collagen & Elastin
    2. Adhesive glycoprotein - fibronectin, laminin
    3. Gel of proteoglycans & hyaluroans.
      1. Interstitial matrix                
      2. Basal membrane
  3. Interstitial Matrix:
    1. Present in space between epithelial, endothelial & smooth muscle cells & in connective tissue
    2. Fibrillar & N.F. collagen, elastin, fibronectin, proteoglycans, hyaluronate
    3. B/M: Amorphous; N. fibrillar collagen (Type IV) Laminin, heparan sulfate, proteoglycans
    4. Collagen: Tensile strength
      a. Most common protein in animals     
      b. 30 a chains: form 14 distinct collagen types
    5. Type I, II, III: fibrillar / interstitial - most abundant
    6. Type IV, V, VI: N. fibrillar, in interstitial tissue & BM
    7. On ribosome:  
      1. Enzyme Modification,: hydroxylation of proline & lysine (vitamin C required)
      2. Pro collage peptidases (Deficiency of Amino peptidase in Ehlers Danlos Type ill) (Tropocollagen)
    8. Oxidation of lysine & hydroxylysine → Cross Linking - important for tensile strength
  4. Collagen:

Type 1: Skin (80%); Bones (90%); Tendons              
Type 2: Cartilage (90%); Vitreous Humor

Type 3: Blood Vessels; Uterus; skin                          
Type 4:  Bone Marrow


Table: Main types of collagens, tissue distribution, and genetic disorders





This is the most abundant collagen of the human body.

It is present in scar tissue, the end product when tissue heals by repair. It is found in tendons, skin, artery walls, the endomysium of myofibrils, fibrocartilage, and the organic part of bones and teeth.

osteogenesis imperfecta, Ehlers–Danlos syndrome, Infantile cortical hyperostosis aka Caffey's disease


Hyaline cartilage, makes up 50% of all cartilage protein. Vitreous humour of the eye.

Collagenopathy, types II and XI


This is the collagen of granulation tissue, and is produced quickly by young fibroblasts before the tougher type I collagen is synthesized. Reticular fiber. Also found in artery walls, skin, intestines and the uterus

Ehlers–Danlos syndrome, Dupuytren's contracture


basal lamina; eye lens. Also serves as part of the filtration system in capillaries and the glomeruli of nephron in the kidney.

Alport syndrome, Goodpasture's syndrome


most interstitial tissue, assoc. with type I, associated with placenta

Ehlers–Danlos syndrome (Classical)


most interstitial tissue, assoc. with type I

Ulrich myopathy and Bethlem myopathy


forms anchoring fibrils in dermoepidermal junctions

epidermolysis bullosa dystrophica (EDM)


some endothelial cells

Posterior polymorphous corneal dystrophy 2


FACIT collagen, cartilage, assoc. with type II and XI fibrils

– EDM2 and EDM3


hypertrophic and mineralizing cartilage

Schmid metaphyseal dysplasia



Collagenopathy, types II and XI


FACIT collagen, interacts with type I containing fibrils, decorin and glycosaminoglycans


transmembrane collagen, interacts with integrin a1b1, fibronectin and components of basement membranes like nidogen and perlecan.


FACIT collagen


transmembrane collagen, also known as BP180, a 180 kDa protein

Bullous pemphigoid and certain forms of junctional epidermolysis bullosa


source of endostatin


epidermal collagen

Atopic dermatitis

  1. Elastin, Fibrillin, & Elastic fibres
    1. Elastic, Fibres: Ability to recoil
    2. Central core with peripheral microfibrillar network
    3. Central core; Elastin (in large Blood Vessels, Aorta, Uterus, Skin, ligaments)
      1. Glycine, Alanine, proline       
      2. Little hydroxyproline, No hydroxylysine Peripheral microfibrillar: Fibrillin (glycoprotein)
      3. Associated with itself or ECM Scaffolding for deposition of elastin & assembly of elastic fibres (Defective → Marfan's syndrome) Adhesive Glycoproteins & Inte9rins:
      4. Property to build ECM component with cell membrane proteins; link ECM components to one another and to cells
    4. Fibronectin: Multifunctional adhesive protein Q
      1. Attaches cells to matrices
      2. 2 chains held by disulfide bones        
      3. Produced by: Fibroblasts, monocytes, endothelial cells, other cells Bind to ECM & cells via receptors which recognize RGD sequence (Arginine-glycine-Aspartic acid) Q
        1. Involved in attachment, spreading, migration of cells.
        2. Increased sensitivity of endothelial cell to proliferative effect of growth factor
    5. Laminin- Most abundant Glycoprotein of basement membrane
      1. Hetero trimeric cross shaped structure
      2. Span. basal lamina; binds to cell surface & matrix comp.
      3. (e. g., Collage Type IV, heparan sulfate)
      4. Alters growth, survival, morphology, differentiation & motility of cells
      5. Angiogenesis: Alignment of endothelial cells → capillary tube
    6. Integrins
      1. Mediate cell attachment to ECM
      2. a(14) & PCS) Chains - 20 types of integrins
      3. E/C domain of integrins bind to many comp. In ECM (by recognizing RGD sequence) Important in organizing actin cytoskeleton of cells and in transduction of signals form ECM to cell interior
      4. Bind to ECM → clustering → focal adhesion (where link to intra cellular cytoskeleton (components) Proteins in focal adhesions: talin, vinculin, a-actinin, tensin, paxillin Mechanical Force → Biochemical signals

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