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
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
- Ehlers–Danlos syndrome
- Scurvy (vitamin C deficiency)
- Menkes disease
- Osteoporosis
Related
- Collagen synthesis
- Hydroxyproline
- Elastin
- Fibrillin-1
- Vitamin C (ascorbic acid)
- Copper
- 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.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: COL1A1: Collagen alpha-1(I) chain (human) (UniProt, 2026); COL3A1: Collagen alpha-1(III) chain (human) (UniProt, 2026); 3DMW: Crystal structure of human type III collagen G982-G1023 containing C-terminal cystine knot (RCSB Protein Data Bank, 2026); PDB-101: Molecule of the Month: Collagen (RCSB Protein Data Bank (PDB-101), 2026); COL1A1 gene: MedlinePlus Genetics (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.