Meet Collagen!

You have more collagen in your body than any other protein. You can find it almost everywhere, but a lot of it lives in your bones, skin, and cartilage.

Although collagen is made by your cells, it works outside of the cells. Collagen is a structural protein, and it is the primary protein that forms the extracellular matrix, or ECM. (The ECM is like a scaffold that organizes all of your cells and gives your tissues extra structure.) So, collagen’s main job is to maintain the shape of your tissues, and by extension, your whole body!

Extracellular matrix proteins are shown forming a network. Cells are held within that network.
The extracellular matrix provides scaffolding for cells.

Collagen is made of three strands, each over 1400 amino acids (protein building blocks) long. Though there are 20+ amino acid options for building proteins, most of collagen’s amino acids are only one of three types: glycine, proline, and hydroxyproline.

Collagen is larger than the average protein, (but is not even close to the biggest one).

Each of collagen’s strands forms a helical shape. One of its key amino acids, glycine, appears in every third position (1-2-Glycine-1-2-Glycine-1-2-Glycine, etc.). This pattern is such that all of the glycine’s point in the same direction in the helix. Glycines love to hang out with other glycines, so this pattern also allows all three helices to be glued together, with all of the glycines in the middle.

Three-dimensional structure model of collagen viewed from two perspectives. Left panel: viewed from the side. Collagen is made of three identical semi-helical strands, and glycine shows up at every third position in the sequence.
Right panel: viewed from the top. Glycines point towards the middle of collagen and keep the strands together.

Proline and hydroxyproline make up most of the rest of collagen strands. They are special because they allow collagen’s helix to twist especially sharply (most protein helices do not include these amino acids). Hydroxyproline is a special kind of amino acid because it cannot be encoded by a DNA sequence. Hydroxyprolines in collagen all start out as prolines, and are modified later.

Proline is converted to hydroxyproline by adding "OH."
Proline can be converted into hydroxyproline.

Transforming proline into hydroxyproline requires vitamin C. Deficiency in vitamin C can prevent collagen from doing its job, which results in scurvy. It should be no surprise that lacking structure in your tissues is a major problem for your body’s health!

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