1. Extra Cellular Matrix (ECM)
Structure, Synthesis, Function, Disease

2. The Extra Cellular Matrix: ECM
Extra Cellular: outside the cell Matrix: structure made from a network of interacting components
The ECM is composed of an interlocking mesh of fibrous proteins and glycosaminoglycans (GAGs).
Components of the ECM are produced intracellularly by resident cells, and secreted into the ECM via exocytosis.

3. Functions of ECM 1-Role in establishing and maintaining cell shape,
migration, mechanical support
2-Anchorage for cells, segregating tissues from one another, and regulating intercellular communication
3-Sequesters a wide range of cellular growth factors, and acts as a local depot for them
4-Essential for processes like growth, wound healing etc

4. What are the major proteins of the ECM
What are the major proteins of the ECM? Collagens, Proteoglycans, Elastin, Fibronectin, Laminin, Tenascin.

5. The collagens
A family of fibrous proteins found in all multicellular animals
They are secreted by connective tissue cells, as well as by a variety of other cell types
They are the most abundant proteins in mammals, constituting 25% of the total protein mass in these animals

6. Structural features Long, stiff, triple-stranded helical structure,
Three collagen polypeptide chains, called α chains, are wound around one another in a ropelike superhelix
A basic unit of mature collagen is called tropocollagen

7. Composition of collagens
Collagens are extremely rich in proline and glycine
It is composed mainly of glycine (33%), proline (13%), 4-hydroxyproline (9%)
Hydroxyproline is unique for collagen and elastin

9. Amino acid sequence
Every third residue is glycine which lies in the center of the triple helix, with the preceding residue being proline or hydroxyproline in a repetitive fashion
pro-Gly-X
hydroxypro-Gly-X

10. Functions of amino acids
Proline stabilizes the helical conformation in each a chain
Glycine allows the three helical a chains to pack tightly together to form the final collagen superhelix

11. Hydroxylysine
Collagen is also composed of hydroxylysine, which serves as attachment sites of polysaccharides making collagen a glycoprotein

12. Lysine
Part of the toughness of collagen is accounted by the cross-linking of chains via lysine residues

13. How?
Some of the lysine side chains are oxidized to aldehyde derivatives, which react with another lysine or another oxidized lysine via the action of lysyl oxidase

16. Types of collagens
There are about 40 collagen genes dispersed throughout the genome and the protein products combine to form more than 28 different types of collagen.
The various collagens and the structures they form all serve the same purpose, to help tissues resist stretching.

17. Classification of collagen
1. Fibril-forming collagens
No interruptions in triple helix
Regular arrangement results in characteristic “D” period of 67 nm
Diameter : nm
Example : Types I, II, III, V, XI

18. Classification of collagen
2. Network-forming collagens
Forms network in basement (Collagen IV) and Descemet’s membrane (Collagen VIII)
Molecular filtration
Example : Types IV, VIII, X

19. Classification of collagen
3. Fibril-associated collagens with interrupted triple helices (FACITs)
Short collagens with interruptions
Linked to collagen II and carries a GAG chain
Found at the surface of fibril-forming collagens
Example : Types IX, XII, XIV

20. Classification of collagen
4. Anchoring collagens
Provides functional integrity by connecting epithelium to stroma
Example : Type VII

21. Classification of collagen
5. Beaded-filament-forming collagens
Form structural links with cells
Example : Type VI
Collagen VI crosslink into tetramers that assemble into long molecular chains (microfibrils) and have beaded repeat of 105 nm

22. Synthesis of collagen
Individual collagen polypeptide chains are synthesized on membrane-bound ribosomes and injected into the lumen of the endoplasmic reticulum (ER) as larger precursors, called pro- chains
In the lumen of the ER, selected prolines and lysines are hydroxylated to form hydroxyproline and hydroxylysine, respectively, and some of the hydroxylysines are glycosylated
Each pro-a chain then combines with two others to form a hydrogen-bonded, triple-stranded, helical molecule known as procollagen
(Continued)

23. Synthesis of collagen
During or following exocytosis, extracellular enzymes, the procollagen peptidases, remove the N-terminal and C-terminal propeptides
The resulting protein, often called tropocollagen (or simply collagen), consists almost entirely of a triple-stranded helix.
Excision of both propeptides allows the collagen molecules to polymerize into normal fibrils in the extracellular space

24. Collagen-related diseases
Collagen is highly cross-linked in tissues where tensile strength is required such as Achilles tendon
If cross-linking is inhibited, the tensile strength of fibers is greatly reduced, collagenous tissues become fragile, and structures tend to tear (skin, tendon, and blood vessels)

25. Diseases associated with collagen
Diseases caused by mutations
Subtypes of osteogenesis imperfecta (collagen I)
Ehlers-Danlos syndrome (collagen I and V)
Alport syndrome (collagen IV)
Certain arterial aneurysms (collagen III)
Ullrich muscular dystrophy (collagen VI)
Certain chondrodysplasias (collagen IX and XI)
Kniest dysplasia (collagen II)

28. Scurvy The formation of hydroxyproline requires vitamin C
Deficiency of vitamin C results in insufficient hydroxylation of proto-collagen and, hence, poor synthesis of collagen, formation of unstable triple helices preventing formation of normal fibrils
Non-hydroxylated procollagen chains are then degraded within the cell
This results in weakening of the collagen resulting in skin and gum lesions and weak blood vessels

29. Types of OI At least four types of osteogenesis imperfecta
Designated as type I through type IV
Type I osteogenesis imperfecta is the mildest form of the condition
Type II is the most severe results in death in utero or shortly after birth
Milder forms generate a severe crippling disease

30. Mutations of OI Mutations in the COL1A1 and COL1A2 genes cause OI
These mutations typically interfere with the assembly of type I collagen molecules
A defect in the structure of type I collagen weakens connective tissues, particularly bone, resulting in the characteristic features of OI
OI types I, II, and IV have an autosomal dominant pattern of inheritance, which means one copy of the altered gene in each cell is sufficient to cause the condition

33. Chondrodysplasias
Mutations affecting type II collagen cause chondrodysplasias, characterized by abnormal cartilage, which leads to bone and joint deformities

34. Ehlers-Danlos syndrome
A heterogenous group of disorders that affect connective tissues, which are tissues that support the skin, bones, blood vessels, and other organs
The signs and symptoms of Ehlers-Danlos syndrome vary from mildly loose joints to life-threatening complications

35. Mutations in Ehlers-Danlos syndrome
Ehlers-Danlos syndrome results from defects in synthesis of either collagen molecules type I, III, or V or in the synthesis of collagen processing enzymes like procollagen N-peptidase, or lysyl hydroxylase resulting in mobile joints and skin abnormalities

36. Non-collagen component of Bone Matrix
Made up of stiffening substances to resist bending and compression (Inorganic matter ).
The bone mineral is an analogue of crystals of calcium phosphate —
hydroxyapatite Ca10(PO4)6(OH)2, a substance that can only be seen
under electron microscopy.
It is this association of hydroxyapatite with collagen fibres which is responsible for the hardness of bone.

37. Elastin The main component of elastic fibers is elastin
A highly hydrophobic protein, which, like collagen, is unusually rich in proline and glycine
But, unlike collagen, is not glycosylated
Contains some hydroxyproline but no hydroxylysine

38. Formation of elastic network
Soluble tropoelastin (the biosynthetic precursor of elastin) is secreted into the extracellular space and assembled into elastic fibers close to the plasma membrane
After secretion, the tropoelastin molecules become highly cross-linked to one another, generating an extensive network of elastin fibers and sheets
The cross-links are formed between lysines by a mechanism similar to that of collagen molecules

39. Elastin structure
The elastin protein is composed largely of two types of short segments that alternate along the polypeptide chain:
hydrophobic segments, which are responsible for the elastic properties of the molecule; and
alanine- and lysine-rich a-helical segments, which form cross-links between adjacent molecules

40. Function of elastic fiber
Elastin is the dominant extracellular matrix protein in arteries
Mutations in the elastin gene causing a deficiency of the protein result in narrowing of the aorta or other arteries as a result of excessive proliferation of smooth muscle cells in the arterial wall
Apparently, the normal elasticity of an artery is required to restrain the proliferation of these cells

41. Diseases of Elastic Fiber
Cutis laxa
Williams syndrome
Buschke-Ollendorff syndrome 
Menkes disease 
Pseudoxanthoma elasticum,
Marfan's syndrome 
defects in copper metabolism (lysyl oxidase)

42. Glycoproteins and Proteoglycans
4/15/2017
Glycoproteins and Proteoglycans
Proteins conjugated to saccharides lacking a serial repeat unit
Glycoproteins
Protein >> carbohydrate
Proteins conjugated to polysaccharides with serial repeat units
Proteoglycans
Carbohydrate >> protein
Glycosaminoglycans
Mucopolysaccharides
HexN: hexosamine
HexUA: hexose uronic acid

43. Glycoproteins
Proteins that contain oligosaccharide chains (glycans) covalently attached to polypeptide side-chains, in a co-translational or posttranslational modification.
(N- Glycosylation), the addition of sugar chains can happen at the amide nitrogen on the side chain of the asparagine.
(O- Glycosylation), the addition of sugar chains can happen on the hydroxyl oxygen on the side chain of hydroxy-lysine, hydroxy-proline, serine, or threonine.

44. Functions of Glycoproteins
Structural
Reproduction
Hormones
Enzymes
Carriers
Inhibitors
Immunological

45. THANK YOU