SKINIPEDIA - Skin Essentials: Collagen, Skin & Wrinkles

Collagen on a Grocery Shelf

Collagen from livestock animals is a familiar ingredient for cooking. Like most proteins, when collagen is heated, it loses all of its structure. The triple helix unwinds and the chains separate. Then, when this denatured mass of tangled chains cools down, it soaks up all of the surrounding water like a sponge, forming gelatin.

collagen protein basement membrane that supports your skin

Ropes and Ladders

We make many different kinds of collagen, which form long ropes and tough sheets that are used for structural support in mature animals and as pathways for cellular movement during development. All contain a long stretch of triple
helix connected to different types of ends. The simplest is merely a long triple helix, with blunt ends. These "type I" collagen molecules associate side-by-side, like fibers in a rope, to form tough fibrils. These fibrils crisscross the space between nearly every one of our cells. The illustration above depicts a basement membrane, which forms a tough surface that supports the skin and many organs. A different collagen– "type IV"–forms the structural basis of this membrane.
Type IV collagen has a globular head at one end and an extra tail at the other. The heads bind strongly together, head-to-head, and four collagen molecules associate together through their tails, forming an X-shaped complex. Using these two
types of interactions, type IV collagen forms an extended network, shown here in light blue. Two other molecules–cross-shaped laminin (bluegreen) and long, snaky proteoglycans (green)–fill in the spaces, forming a dense sheet.

 

 

Exploring the Structure

A special amino acid sequence makes the tight collagen triple helix particularly stable. Every third amino acid is a glycine, and many of the remaining amino acids are proline or hydroxyproline. A classic triple helix is shown here, and may be viewed in the PDB file 1cag (above). Notice how the glycine forms a tiny elbow packed inside the helix, and notice how the proline and hydroxyproline smoothly bend the chain back around the helix. In this structure, the researchers placed a larger alanine amino acid in the position normally occupied by glycine, showing that it crowds the neighboring chains.

This collagen helix contains a segment of human collagen, and may be viewed in the PDB file 1bkv (below). Notice that the top half is very uniform, where the sequence is the ideal mixture of glycine and prolines. At the bottom, the helix is less regular, because many different amino acids are placed between the equally-spaced glycines.

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