Focus protein: Collagen

Keeping animals in shape

Protrumps card for collagen

Illustration from the RCSB Protein Databank.

Collagen comes in different varieties, but they all have the same basic structure: a sequence of three amino acids repeated hundreds of times. The sequence is Gly-Pro-X, where Gly is glycine, Pro is often proline and X is usually a modified form of proline called hydroxyproline. This amino acid sequence allows the polypeptide chain to fold into a helix (this is different from the alpha helix seen in the secondary structure of some proteins). Three collagen helices then wind round one another to form a strong, stable collagen triple helix. These helices covalently bond with each other to create fibrils, which can, in turn, be bundled into collagen fibres.

The collagen triple helix is the most common protein structure in the body. It is found in bones and teeth, tendons, ligaments and cartilage, the walls of arteries, and one of the thin layers of the cornea that protects our eyes. Altogether, around one-third of all the protein in vertebrates is collagen.

Collagen fibrils combine with other materials in the extracellular matrix, which fills the space between cells in different ways in different tissues. In bone, for example, calcium phosphate crystals form in the gaps between collagen fibres to harden it.

Partially degraded collagen from the bones and skin of animals makes gelatine, which is the substance that gives marshmallows and sweets their squishy texture.

About this resource

This resource was first published in ‘Proteins’ in January 2014.

Cell biology
Education levels:
16–19, Continuing professional development