What are the steps in modification of collagen in the ER?
- Synthesis and entry of chain into the lumen of the RER
- Cleavage of signal peptide
- Hydroxylation of proline and lysine residues
- Addition of N-linked ogliosaccharides
- Addition of galactose to hydroxylysine residues
- Chain alignment and formation of disulphides bonds
- Formation of triple helical procollagen (C- to N-terminus as disulphide bonds at C-terminus)
- Completion of O-linked ogliosaccharide by addition of glucose
- Transported in transport vesicle
- Exocytosis into extracellular space
- Removal of N- and C-terminal propeptides
- Lateral association of collagen molecules and covalent cross-linking
- Aggregation of fibrils
What is the basic unit of collagen?
How many polypeptides is collagen made up of?
3 alpha chain
What is the formula for the alpha chain amino acid sequence for collagen?
Glycine is in every 3rd position along each alpha chain (Gly-X-Y)n
What is the structure of the collagen helix?
Right handed triple helix
What is the advantage of the triple helix structure of collagen?
- High tensile strength
Why is Glycine the repetitive amino acid in collagen?
It is the only amino acid with a small enough side chain to fit in the middle of the helix
What is the most common amino acid in the X position?
Proline (or hydroxyproline)
What bonds form between the alpha chains to stabilise the structure?
What bonds form between collagen molecules making collagen fibrils?
What are two types of post-translational modification?
- Proteolytic cleavage - breaking peptide bonds to remove part of protein
- Chemical modification - addition of functional groups to amino acid residues