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Biochemistry · Protein

Collagen Triple Helix 3D Structure

The most abundant protein in mammals: three chains wound into a rope-like triple helix, with glycine at every third position.

Collagen gives skin, tendon, bone and cartilage their strength. Its molecule is a long, thin rope of three chains, each a repeat of glycine, X, Y, where X is often proline and Y often hydroxyproline. A full collagen molecule is about 300 nanometres long; this crystal holds a short stretch, a peptide built to show how the triple helix is made.

Also called Collagen or Tropocollagen.

Three grey strands twisted round each other into a straight, rope-like triple helix, standing upright.
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Three chains, one rope

The collagen molecule is a triple helix: three chains wound round each other like the strands of a rope. A full molecule is about 1.5 nanometres thick and 300 nanometres long; this piece is nearly 9 nanometres long.

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View 1 of 6: Three chains, one rope

Download the pictureDownload the atoms (PDB)Checked against its sources on 25 October 2026.

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The Collagen Triple Helix structure, explained

  1. 01Three chains, one rope

    The collagen molecule is a triple helix: three chains wound round each other like the strands of a rope. A full molecule is about 1.5 nanometres thick and 300 nanometres long; this piece is nearly 9 nanometres long.

  2. 02One chain of three

    Each chain is not an alpha helix but a looser, left-handed helix with about three amino acids per turn. It is stable only as part of the triple helix, held by hydrogen bonds to the other two chains.

  3. 03Glycine at every third place

    The sequence repeats glycine, X, Y. Glycine sits at the centre of the triple helix, where there is no room for a larger side chain. In type I collagen, a mutation that replaces one glycine with anything bigger untwists the helix locally, and is a common cause of osteogenesis imperfecta, brittle bone disease.

  4. 04Proline and hydroxyproline

    Proline and hydroxyproline make up a large share of collagen. Their rings fix the twist of each chain, and the hydroxyl of hydroxyproline adds stability, so the helix holds together at body temperature.

  5. 05Why scurvy weakens tissues

    Prolyl hydroxylase, the enzyme that turns proline into hydroxyproline inside the cell, needs vitamin C. Without it, collagen chains are poorly hydroxylated and form weaker triple helices, and the gums, skin and blood vessels it holds together start to fail: scurvy.

  6. 06A real collagen sequence

    The middle of this peptide is a stretch of human type III collagen, with no proline or hydroxyproline in it. The study showed that the triple helix is wound slightly differently there, so its shape follows its sequence.

Parts

What each part does

Chain 1
One of the three chains, about 30 amino acids here. Within the triple helix each chain twists into a narrow left-handed helix, with about three amino acids per turn.
Chain 2
The second chain, the same sequence as the first. In the helix it sits one amino acid along from its neighbour, so the glycines of the three chains are staggered.
Chain 3
The third chain. The three together twist round a common axis into a right-handed superhelix, the triple helix.
Glycine
Every third amino acid. Glycine has only a hydrogen for a side chain, small enough to fit at the crowded centre of the triple helix, where the three chains touch.
Proline
Often in the X position of glycine, X, Y. Its ring holds the chain in the twisted shape the triple helix needs.
Hydroxyproline
Proline with a hydroxyl added after the chain is made, by prolyl hydroxylase, an enzyme that needs vitamin C. It is usually in the Y position and makes the triple helix more stable.
Stretch of type III collagen
ITGARGLAG, nine amino acids of human type III collagen. With no proline or hydroxyproline in it, the helix here is wound a little differently, which the study set out to show.

The structure

Where these atoms come from

Structure
PDB 1BKV
What it is
Collagen-like peptide with a region of human type III collagen
Organism
Synthetic, with a sequence from Homo sapiens
Method
X-ray diffraction, 2 Å resolution
Deposited
1998
Atoms shown
563, without water or hydrogens
Paper
Kramer RZ and others, Nat Struct Biol 1999

Coordinates from the Protein Data Bank, free of all copyright (CC0). Water and hydrogens are left out, and the molecule is turned to face you; every atom is where the experiment placed it.

Dictionary

The terms to know

Practise it

The quizzes and cards that fit

Next to it

More molecules

Sources

Where the facts come from

Written by biofideX from these sources. Drawn with 3Dmol.js (Rego and Koes, Bioinformatics 2015).

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