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[Biochemistry](https://durgical.com/en/biochemistry/) · Protein

# Collagen

Collagen is the body's most abundant protein: three braided chains that give strength to bone, skin, tendons and vessels.

Updated 2026-11-01

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## Key facts

- Triple helix of three α chains (each a left-handed helix, wound into a right-handed superhelix), with the repeating Gly–X–Y sequence.
- Rich in glycine (≈ 1/3), proline and hydroxyproline; hydroxyproline and hydroxylysine are formed after translation.
- Type I (≈ 90 % of body collagen: bone, skin, tendon, dentine, cornea) is a heterotrimer of two α1(I) chains and one α2(I).
- Type II: cartilage and vitreous humour. Type III: vessels, fetal skin, granulation tissue. Type IV: basement membranes (a network, not fibrils).

**Also called**
Type I collagen, Tropocollagen

**Genes**
COL1A1, COL1A2, COL3A1

**Structure (PDB)**
[3DMW](https://www.rcsb.org/structure/3DMW)

## Structure

- Structure 3DMW is a human type III collagen fragment (residues 982–1023) with its C-terminal cystine knot; it shows the triple helix, not the full fibril.
- In the fibril, tropocollagen molecules (≈ 300 nm) are staggered and leave gaps where bone hydroxyapatite crystals are laid down.

## Regulation

- Synthesis is stimulated by TGF-β and vitamin C and inhibited by glucocorticoids.
- It is degraded by matrix metalloproteinases (collagenases, MMPs), held in check by tissue inhibitors (TIMPs).

## Inhibitors and toxins

- Lack of vitamin C (proline is not hydroxylated)
- β-aminopropionitrile (lathyrism: blocks lysyl oxidase)
- Penicillamine (interferes with cross-links)

## Clinical notes

- Osteogenesis imperfecta: COL1A1 or COL1A2 variants; bones that break with minimal trauma and blue sclerae.
- Vascular Ehlers–Danlos syndrome: COL3A1 variants; arteries, bowel and uterus that rupture.
- Alport syndrome (type IV collagen): haematuria, deafness and eye changes; in Goodpasture syndrome antibodies attack type IV collagen in glomerulus and lung.
- Keloids and fibrosis (cirrhosis, pulmonary fibrosis) are excess collagen deposition.

## Related conditions

- [Osteogenesis imperfecta](https://durgical.com/en/conditions/osteogenesis-imperfecta/)
- [Ehlers–Danlos syndrome](https://durgical.com/en/conditions/ehlers-danlos-syndrome/)
- [Scurvy (vitamin C deficiency)](https://durgical.com/en/conditions/scurvy/)
- [Menkes disease](https://durgical.com/en/conditions/menkes-disease/)
- [Osteoporosis](https://durgical.com/en/conditions/osteoporosis/)

## Related

- [Collagen synthesis](https://durgical.com/en/biochemistry/topics/collagen-synthesis/)
- [Hydroxyproline](https://durgical.com/en/biochemistry/molecules/hydroxyproline/)
- [Elastin](https://durgical.com/en/biochemistry/enzymes/elastin/)
- [Fibrillin-1](https://durgical.com/en/biochemistry/enzymes/fibrillin-1/)
- [Vitamin C (ascorbic acid)](https://durgical.com/en/biochemistry/molecules/vitamin-c/)
- [Copper](https://durgical.com/en/biochemistry/topics/copper/)
- [Protein structure and folding](https://durgical.com/en/biochemistry/topics/protein-structure-and-folding/)

## Test yourself

Think of the answer, then tap the question to see it.

## Which amino acid sequence repeats in collagen?

Gly–X–Y, often with proline at X and hydroxyproline at Y; glycine is the only residue that fits the centre of the triple helix.

## Which collagen type fails in osteogenesis imperfecta?

Type I, from COL1A1 or COL1A2 variants: bone, dentine and sclera are weak.

## Which collagen type forms basement membranes?

Type IV, which builds a network instead of fibrils; it is affected in Alport syndrome and targeted by antibodies in Goodpasture syndrome.

## Which collagen type predominates in granulation tissue?

Type III; as the scar matures it is largely replaced by type I.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: [COL1A1: Collagen alpha-1(I) chain (human)](https://www.uniprot.org/uniprotkb/P02452/entry) (UniProt, 2026); [COL3A1: Collagen alpha-1(III) chain (human)](https://www.uniprot.org/uniprotkb/P02461/entry) (UniProt, 2026); [3DMW: Crystal structure of human type III collagen G982-G1023 containing C-terminal cystine knot](https://www.rcsb.org/structure/3DMW) (RCSB Protein Data Bank, 2026); [PDB-101: Molecule of the Month: Collagen](https://pdb101.rcsb.org/motm/4) (RCSB Protein Data Bank (PDB-101), 2026); [COL1A1 gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/col1a1/) (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/biochemistry/enzymes/collagen/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/enzymes/collagen/