Collagen Flashcards
What is collagen?
Family of fibrous proteins that form insoluble fibres
What property makes them appropriate for bone, tendon, cartilage etc
High tensile strength
Structure?
Consists of 3 polypeptide chains. These vary between collagen types
1ary structure
Every 3rd residue is Gly. Repeating sequence is Gly-X-Y. X is usually Pro (Gly-Pro-Y) and Y is usually Lys (Gly-X-Lys)
Why is every 3rd residue Gly?
- Every 3rd residue of each polypeptide passes through centre of triple helix
- Gly is the amino acid with the smallest side chain so is only one that can fit in centre
What happens when Gly residue is replaced with an amino acid with a larger side chain during a mutation?
Helix can no longer wind so tightly, leads to ineffective collagen
2ary structure
Each polypeptide chain forms a left-handed helix with 3.3 residues per turn (collagen helix)
What is normal amount of residues per turn?
3.6
3ary structure
- 3 polypeptide chains lie parallel and twist round each other
- This forms triple helix (right handed)
What is name of triple helix?
Procollagen (before removal of extension peptides)
Where is collagen finally secreted into?
Extracellular spaces of connective tissue
When do post-translational modifications occur?
Occurs before polypeptide chains form helix
Which residues are hydroxylated?
Proline and Lysine
What are the products of this hydroxylation?
Hydroxyproline (Hyp) and Hydroxylysine (Hyl)
What enzymes are involved in hydroxylation?
Prolyl hydroxylase and lysyl hydroxylase
What is required as co-factor?
Vitamin C
What causes scurvy?
Vitamin C deficiency; Hyp and Hyl and not synthesised. Results in weakening of collagen fibres
Symptoms of scurvy
Skin lesions, fragile blood vessels, poor wound healing
What is name of structure after post-translational modifications?
Procollagen (triple helix)
What are extension peptides?
Collagen chains are synthesised with additional amino acid chains at each end (N & C termini)
What forms between C-terminal extensions of neighbouring polypeptide chains?
Disulphide bonds
What enables these bonds to form?
Extensions often contain Cys
What is purpose of these bonds?
- Facilitates triple helix assembly
2. Help prevent premature aggregation
When are extension peptides removed?
Removed after secretion into extracellular space.
