Dr Ritesh Shiwakoti
• 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
• 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.
• Gel- extracellular matrix or vitreous humor of eye.
• Tight bundles- Tendons
• Stacked- as in Cornea
• Fibers arranged at an angle- Bones
TYPES OF COLLAGEN
Collagen type I
• Found in the supporting elements of high tensile strength.
• Found in bone, skin, tendon, muscles, cornea and walls of
Collagen type II
• Found in cartilaginous tissues.
• Found in inter verteberal disk, vitreous body and hyaline
Collagen type III
• Found in distensible tissues.
• Fetal skin, blood vessels.
Collagen type IV
• Found in the basement membranes and muscles.
Collagen type VII
• Beneath stratified squamous epithelia
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
• 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
- Hydroxyl group of hyl residues of collagen may be
- Most commonly, glucose & galactose are sequentially
attached to polyp chain prior to triple-helix formation
• 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.
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.
3. Emphysema results from destruction of connective tissue of
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
• Collagens are widely employed in the construction of artificial
skin substitutes used in the management of severe burns &
• 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
• 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.