1. EXTRACELLULAR MATRIX(ECM)
Dr. Eman Khairy
Lecturers of Medical biochemistry & Molecular Biology

2. By the end of this topic you will be able to:
Recognize the importance of ECM and its component in the health and diseases.
Describe the structural and functional properties of collagen and elastin, the major proteins in ECM.
Describe the general properties of proteoglycans , fibronectin, and laminin.

3. ECM contains 3 major classes of biomolecules
The space between cells that bind cells and tissue together
ECM contains 3 major classes of biomolecules
Fibrous
(structural protein)
Collagen
Elastin
Fibrillin
Proteoglycan
Chondrotin sulphate
Dermatan sulphate
Hyalouronic acid
Adhesion proteins
Fibronectin
Laminin
Integrin

4. ADHESION MOLECULES
Link component of matrix protein to each other and to cells
Cell A
Direct cell to cell contact
adhesion proteins
Cell B
ECM
cell to ECM contact

5. Specific domain bind to specific cellular receptor
Adhesion proteins
Cytoskeletal proteins
Integrin
Adhesion proteins
Specific domain bind to specific cellular receptor
spans cell membrane and interact with intracellular protein , Actin filamints

6. Collagen Collagen is glycoprotein
28-30 types in human
Provides Extracellular framework of animal body
The main component of loose connective tissue ,blood vessels ligaments, tendons, bone and skin.
The most abundant protein in the body, making 25%-35% of all the whole-body proteins.
Collagen is glycoprotein

7. Collagen structure Collagen fibers Collagen fibrils
Tropocollagen (triple helix)
Single chain of amino acids

8. Triple helical collagen supercoils
Collagen structure
(Gly –X-Y )n
Y proline
Glycine
X any amino acid
Triple helical collagen supercoils
(right handed)

9. Collagen structure Glycine Proline Lysine ,hydroxylysine
Third amino acid of collagen
33%
Proline
Y is frequently proline or hydroxyproline
21% of collagen
Responsible for left handed alpha helix
Lysine ,hydroxylysine
Some Y position
Form interchain covalent cross link.
Form O linked glycosidic bond

10. Hydroxyproline and hydroxylysine
Result from hydroxylase enzyme.
Hydroxylation need vitamin C
TYPE OF POST-TRANSLATIONAL MODIFICATION
Hydroxylysine is site for attachment of disaccharide.

11. Absent amino acids in collagen
Tryptophan
Cysteine

12. Biosynthesis 1. Formation of pro-α chains 2. Hydroxylation
3. Glycosylation
4. Assembly and secretion
5. Extracellular cleavage of procollagen molecules
6. Formation of collagen fibrils
7. Cross-link formation
Extended Modular Program

13. Where is collagen synthesized?
Osteoblast
Chondroblast
Fibroblast

14. 1. Formation of pro-α chains
The newly formed polypeptide (prepro-α chains) contain a special signal sequence at their n-terminal ends
Directs the passage of the prepro-α chain into the lumen of the RER
Then it is cleaved giving a precursor of collagen called a pro-α chain
Extended Modular Program

15. By prolyl hydroxylase and lysyl hydroxylase enzymes
2. Hydroxylation
Proline and lysine residues are hydroxylated to hydroxyproline and hydroxylysine
By prolyl hydroxylase and lysyl hydroxylase enzymes
Extended Modular Program

16. Some hydroxylysine residues are glycosylated with
3. Glycosylation
Some hydroxylysine residues are glycosylated with
glucose or galactose

17. Extended Modular Program

18. 4. Assembly and secretion
tropocollagen
tropocollagen
5. Extracellular cleavage of procollagen molecules
Propeptides
Extended Modular Program

19. 6. Formation of collagen fibrils
Extended Modular Program

20. Oxidative deamination allysine + hydroxyallysine
7. Cross-link formation
Oxidative deamination
Cu dependent
allysine + hydroxyallysine
Covalent crosslink
Extended Modular Program

21. Extended Modular Program
Summary of biosynthesis
Extended Modular Program

22. Degradation of collagen
Normal collagen is highly stable
Long half life up to several months
collagenase

23. Covalent crosslink between triple helical units
Lysyl oxidase
Cu dependent
Oxidatively deaminate some lysyine and hydroxylysine
Covalent crosslink
Form allysine +
hydroxyallysine.

24. Difference between collagen helix and alpha helix
Backbone of polypeptide chain twisted about alpha carbon forming a helix
Superhelix of 3 chains wrapped around each other in RT haded
RT handed twist
Each single chain is LT handed
Intrachain hydrogen bond
interchain hydrogen bond
3.6 aa /turn
3 aa /turn
No specific aa sequence.
(Glycine X-Y)n

25. Collagen structure function relationship
Tight parallel fibers
Provide great tensile strength
Collagen tendon
Arranged at angle to each other.
Resist mechanical shear
Collagen of bone and teeth
Loosely woven ,flexible
Collagen of skin
Transparent with minimal scattering of light
Collagen of cornea of eye
Form gel.
Viterous humor of eye

26. Mention 2 diseases that are related to collage?
1- Scurvey
2- Osteogenesis imperfecta

27. Scurvey (Vit. C deficiency)
Defect in hydroxylation of proline and lysine
Weak and fragile collagen
Collagen become unstable and easily degraded
Bleeding per gum, swollen joint, poor wound healing, fragile bone and easily fracture

28. Osteogensis imperfecta
Single base mutation
Replacement of glycine with bulky amino acid
Weak collagen
Fragile bone with easily bone fracture from minor trauma

29. Elastin
Major protein component of elastic tissues such as arteries, lungs, skin
Highly cross linked ,insoluble, amorphous
Rubber like consistency

30. Elastin has no regular 2ry structure ,only random coils
Microfibrils
Elastic fibers

31. glycine , valine , alanine and proline Little hydroxyproline
Tropoelastin
contain
glycine , valine , alanine and proline
Rich in lysine
Little hydroxyproline
No hydroxylysine

32. Elastic fibers synthesis
Tropoelastin molecules
Desmosine crosslink
(3 allysyl residues+ unaltered lysine )
lysyl oxidase

33. Elastin is highly stable up to 70 years.
Elastin degradation
Elastin is highly stable up to 70 years.
Elasin is degraded by elastase enzyme releases by neutrophils.

34. In lung, elastin is present
Elastin is protected from degradation of elastase by α1 anti-trypsin which inactivate elastase
If there is α1 anti-trypsin defficiency
Increase elastase activity
Increase degradation of elastin
Lung emphysema
destruction in connective tissue of alveolar wall which cannot be regenerated

35. α1- antitrypsin deficiency
Homozygous genetic disease
There is deficiency in α1- antitrypsin (α1 antiprotease)
Lung emphysema occurs
Treated by IV α1- antitrypsin every week.

36. Smoking cause oxidation and subsequent inactivation of methionine in α1- antitrypsin.
So, α1- antitrypsin can’t bind to elastase .
This will be lead to lung emphysema.

37. Differences of elastin from collagen
Many different genetic types
Single genetic type
Triple helix
No (random coils)
(Gly-x-y)n No
Hydroxylysine is present
Contain carbohydrate
Intramolecular aldol cross-links
Intramolecular desmosine cross-links
Widely distributed
Large blood vessels,skin ,elastic ligaments
High tensile strength + no stretch
Stretch+ recoil

38. Carbohydrate chain (95%)
Proteoglycans
Core protein
(5%)
Carbohydrate chain (95%)
Proteoglycan

39. Glycosaminoglycans (GAG)
Core protein
Unbranched
Long Linear
Repeated disaccharide units
Amino sugar is sulphated or acetylated
Covalent crosslink
Disaccharides Amino sugar+ uronic acid

40. Proteoglycan monomer is polyanion due to the presence of COO ,SO3
1-The chains of repeating disaccharide units remain separated by repulsion between negative charges-
Bottle brush appearance of proteoglycan

41. Proteoglycan monomer is polyanion due to the presence of COO ,SO3
2-The chains bind cations as Na and K and attract water by osmotic pressure into ECM-
Gel like consistency of ECM

43. PROTEOGLYCAN AGGREGATES
Hyalouronic acid
PROTEOGLYCAN AGGREGATES
Linker protein

45. Proteoglycans Proteoglycan monomer Proteoglycan aggregates
Proteoglycan monomer +hyalouronic acid +linker protein(non covalent)
Proteoglycan monomer
Glycosaminoglycans + core proteins (covalent link)

46. Classification of proteoglycan is based on
Disaccharide unit
Type of glycosidic bond
Degree and location of sulfate group

47. Classification of proteoglycan into six groups
Hyaluronic acid
(only free GAG, No core protein, non sulfated )
chondroitin sulfate
dermatan sulfate
heparan sulfate
keratan sulfate
Heparin
(secreted in blood by mast cells,not present in ECM)

48. Proteoglycan functions
All the proteoglycan classes determine structural organization of the matrix
Each class has also special function

49. LAMININ Hetero trimeric
The second most abundant protein in basal laminae after type IV collagen
Hetero trimeric
Alpha subunit
Beta subunit
Gamma subunit

50. Laminin Functions
It can form networks of web like structure to resist tensile force in basal lamina.
Bind to type IV collagen ad other components in ECM and integrin ,so provide additional support.

51. Fibronectin Glycoprotein of large MW
Formed of 2 identical subunits joined by 2 disulfide bridges.

52. Fibronectin Fibronectin has binding sites for : Fibrin Collagen
Heparin
DNA
Cell surface receptor

53. Fibronectin provide a bridge between actin of the cell and ECM
Fibronectin interact with fibronectin receptors
(integrin)
Integrin interact with actin microfilaments

54. Fibronectin Sites
ECM
Soluble form in plasma

55. Fibronectin Functions
Cell migration
Communicates exterior of the cell with its interior
Bind to the platelets during blood clotting

56. How the tumor cells metastasize?
Tumor cells secrete less than normal amounts of adhesion protein
Allow more free movements within ECM
Increase the potential for the tumor cells to leave their original location

57. Medical importance of ECM
Infection spread
Metastasis
Rheumatoid arthritis
Alteration of renal glomeruli
Genetic defect
Osteogenesis imperfecta
Mucopolysaccharidosis

58. The link between ECM and disease
1- Infection spread: Infectious agents secrets hyluronidase enzyme which degrade hyalouronic acid. 2- Cancer cell metastasize: Through alternation of integrity of ECM (i.e secret less amount of fibronectin).

59. 3- Rheumatoid disease and osteoarthitis may occur due to damage in ECM
3- Rheumatoid disease and osteoarthitis may occur due to damage in ECM. 4- Alternation in renal glomeruli will lead to protein excretion in urine. 5- osteogenesis imperfecta 6- Mucopolysaccharidosis: due to defect in lysosomal enzyme which degrade mucopolysaccharides ( old name of GAG)

60. Mucopolysaccharidosis
Gradual deterioration of health and death in childhood.
Accumulation of large quantities of GAGs in various tissues
Defect in normal degradation of molecules of ECM
Defeciencies of lysosomal enzymes