synthesis
Last reviewed 01/2018
Collagen is an excellent example of the production of a complex protein structure from a simple amino acid chain. It is made in cells such as fibroblasts:
- individual polypeptide chains are synthesized on membrane-bound ribosomes according to mRNA templates; this is the pro-alpha chain
- a signal peptide on the polypeptide ensures that the chain is passed into the lumen of the endoplasmic reticulum
- proline and lysine residues on the chain are hydroxylated
- some hydroxylysine residues may be glycosylated
- a triple alpha helix of 3 polypeptide chains forms spontaneously; this is procollagen:
- hydroxyproline forms interchain hydrogen bonds
- hydroxylysine cross-links collagen molecules
- procollagen is secreted into the extracellular space where proteolytic enzymes cleave the terminal peptides
- resulting tropocollagen molecules spontaneously combine with other tropocollagen molecules to form linear array within collagen fibril
- collagen fibrils orientate themselves along the line of collagen fibre made from several collagen fibrils