S13 Post-translational Processing of Proteins Flashcards
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?
Tropocollagen
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?
- Non-extensible
- Non-compressible
- 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?
Hydrogen bonds
What bonds form between collagen molecules making collagen fibrils?
Covalent bonds
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
