COLLAGEN FIBERS

Dr Ritesh Shiwakoti

MScD Prosthodontics

INTRODUCTION

• Collagen is the main structural protein of the various connective tissues in animals. As the main component of connective tissue, it is the most abundant protein in mammals , making up from 25% to 35% of the whole-body protein content.

• Collagen, in the form of elongated fibrils, is mostly found in fibrous tissues such as tendons, ligaments and skin. It is also abundant in corneas, cartilage, bones, blood vessels, the gut, intervertebral discs and the periodontium in teeth.

• Collagen and Elastin are the examples of fibrous proteins.

• These are basic structural elements.

• These proteins have special mechanical properties.

• They are found as components of skin, connective tissue, blood vessels, sclera and cornea of eye.

• It is the most abundant protein in the body.

• It is long, rigid structure in which three polypeptides are wound around one another in a rope like fashion.

• These polypeptides are called α-helix

• They are arranged in a triple helix.

• They are found everywhere in the body, but their type is dictated by their structural role in a particular organ.

• Example:

• Gel- extracellular matrix or vitreous humor of eye.

• Tight bundles- Tendons

• Stacked- as in Cornea

• Fibers arranged at an angle- Bones

TYPES OF COLLAGEN

Fibril-Forming:

Collagen type I

• Found in the supporting elements of high tensile strength.

• Found in bone, skin, tendon, muscles, cornea and walls of blood vessels.

Collagen type II

• Found in cartilaginous tissues.

• Found in inter verteberal disk, vitreous body and hyaline cartilage.

Collagen type III

• Found in distensible tissues.

• Fetal skin, blood vessels.

Network- Forming:

Collagen type IV

• Found in the basement membranes and muscles.

Collagen type VII

• Beneath stratified squamous epithelia

Fibril- Associated:

Collagen type IX

• Found in cartilage

Collagen type XII

• Tendon, ligaments

STRUCTURE OF THE COLLAGEN

Amino acid sequence: collagen is rich in Pro & Gly, both important in formation of triple-stranded helix.

• Pro facilitates formation of helical conformation of each α-chain because its ring causes “kinks” in peptide chain.

• Gly, smallest aa, is found in every 3rd position of the polyp chain. It fits into restricted spaces where the 3 chains of the helix come together

• Gly residues are part of a repeating sequence, -Gly-X-Y-, X: frequently Pro, Y: often hydroxyproline or hydroxylysine

• Thus, most α-chain can be regarded as a polyp whose seq can be represented as (-Gly-X-Y-)333

Triple helical structure: unlike most globular proteins that are folded into compact structures, collagen, a fibrous protein, has an elongated, triple helical structure that places many of its aa’s side chains on surface of the triple helical molecule

- This allows bond formation b/w exposed R-groups of neighboring collagen monomers aggregation into fibers

Hydroxyproline & hydroxylysine:

• Collagen contains hyp & hyl, not present in most other proteins

• These residues result from hydroxylation of some Pro & Lys residues after incorporation into polyp chains

• Hydroxylation is an e.g. of post-translational modification

• Hydroxylation of Pro is important in stabilizing triple-helical structure of collagen, it maximizes interchain H-bond formation

Glycosylation:

- Hydroxyl group of hyl residues of collagen may be enzymatically glycosylated

- Most commonly, glucose & galactose are sequentially attached to polyp chain prior to triple-helix formation

DIFFERENT TYPES OF COLLAGEN

• Collagen• Elastin• Oxytalin• Elauin(PROVIDES TENSILE STRENGTH)

Non Collagenous proteinsProteoglycans, HyaluronanLipids , Water(Provides Compressive Strength)

• The collagen of PDL is largely Type I , with lesser amounts of type III , IV , VI and XII .

• Fibril Collagens include type I , III , V that generally co distributes with collagen type I. Higher portion of collagen III usually seen in foetal tissues.

• Collagen Type IV does not form fibrils and is found in basement membranes of neurovascular bundles and other PDL cells. Though this collagen is specifically associated with basement membranes , it also plays role in maintaining the elastic system of the vasculature of the gums.

• Collagen fibers of the periodontium ( particularly Type I ) provide the structural requirements to withstand intrusive forces of mastication ( tooth support ) and also to accommodate growing tooth in mammals.

COLLAGEN DISEASES

1. Ehlers-Danlos syndrome (EDS):EDS can result from deficiency of collagen processing enzymes (e.g., lysyl-hydroxylase deficiency or pro-collagen peptidase deficiency), or from mutations in aa sequences of collagen types I,III, or V.

2.Osteogenesis imperfecta

3. Emphysema results from destruction of connective tissue of alveolar walls

4. Alport Syndrome: Collagen involved- type IV (found in the basement membrane of glomerulas.

- Hematuria - renal diseases

5. Epidermolysis bullosa: Due to alteration of Collagen type VII

- skin breaks - blister formation

6. Scurvy: impaired synthesis of collagen due to deficiencies of prolyl and lysyl and lysyl hydroxylases . bleeding gum -delayed wound healing

Genetic diseases due to Collagen synthesis

MEDICAL USES

• Collagens are widely employed in the construction of artificial skin substitutes used in the management of severe burns & beauty treatments.

• Collagen is also used to make the pennis bigger.

• Collagen is also sold commercially as a joint mobility supplement. This lacks supportive research as the proteins would just be broken down into its base amino acids during digestion, and could go to a variety of places besides the joints depending upon need and DNA orders.

• Collagen is now being used as a main ingredient for some cosmetic makeup.

• Recently an alternative to animal-derived collagen has become available. Although expensive, this human collagen, derived from donor cadavers, placentas and aborted fetuses, may minimize the possibility of immune reactions.