Biochemistry · Topic
Glycosaminoglycans (mucopolysaccharides) !
Glycosaminoglycans are long, negatively charged sugar chains that hold water and give bulk and toughness to cartilage and connective tissue.
Updated 2026-11-01
Key facts
- Unbranched chains of repeating disaccharides: an amino sugar (glucosamine or galactosamine) + a uronic acid (glucuronic or iduronic) or galactose.
- Strongly negative (sulfates and carboxyls): they attract Na⁺ and water and form gels that resist compression.
- Types: hyaluronic acid (no sulfate, no protein), chondroitin sulfate (cartilage), dermatan sulfate (skin, valves), heparan sulfate (basement membranes), heparin (mast cells) and keratan sulfate (cornea, cartilage).
- Except hyaluronan, they attach to a core protein (proteoglycan), such as cartilage aggrecan.
- They are broken down in lysosomes; defects cause the mucopolysaccharidoses, with dermatan and heparan sulfate in urine.
In detail
- 1. Synthesis takes place in the ER and Golgi: sugars arrive as UDP-sugars (UDP-glucuronate comes from UDP-glucose).
- 2. The chain is anchored to a serine of the core protein through a linker tetrasaccharide (xylose-galactose-galactose-glucuronic acid).
- 3. Once built, the chain is modified: sulfation and epimerisation of glucuronate to iduronate.
- 4. Hyaluronan is made differently: at the plasma membrane, with no core protein, and it can reach millions of daltons.
- 5. In the lysosome, exo-enzymes remove one sugar or sulfate at a time from the end; if one is missing, breakdown stops there.
- 6. Roles: joint and vitreous lubrication (hyaluronan), cartilage toughness (aggrecan), the glomerular basement membrane filter (heparan sulfate) and anticoagulation (heparin with antithrombin).
- Also called
- GAGs, Mucopolysaccharides, Proteoglycans
Clinical notes
- Mucopolysaccharidoses: coarse facial features, hepatosplenomegaly, dysostosis multiplex, stiff joints, valve disease and, in some, corneal clouding or cognitive decline.
- MPS I (Hurler) and II (Hunter) store dermatan and heparan sulfate; Hunter does not cause corneal clouding.
- Heparin uses its negative charge to bind antithrombin and speed up the inhibition of thrombin and factor Xa.
Related conditions
- Hurler syndrome (mucopolysaccharidosis type I)
- Hunter syndrome (mucopolysaccharidosis type II)
- I-cell disease (mucolipidosis II)
- Knee Osteoarthritis
Related
- Hyaluronic acid (hyaluronan)
- α-L-Iduronidase
- Carbohydrate chemistry
- Lysosomal storage diseases
- UDP-glucose
Test yourself
Think of the answer, then tap the question to see it.
Why do glycosaminoglycans form gels that resist compression?
Their negative charges attract cations and water; the hydrated chain fills a large volume and resists being squeezed.
Which GAG has no sulfate and no core protein?
Hyaluronic acid (hyaluronan).
Which GAGs appear in the urine in MPS I and II?
Dermatan sulfate and heparan sulfate.
Which sugar distinguishes dermatan sulfate from chondroitin sulfate?
Iduronic acid, formed by epimerisation of glucuronic acid.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Glycosaminoglycan metabolism (Reactome, 2026); Heparan sulfate/heparin (HS-GAG) metabolism (Reactome, 2026); Chondroitin sulfate/dermatan sulfate metabolism (Reactome, 2026); Hyaluronan metabolism (Reactome, 2026); MPS I - Hurler syndrome (HS-GAG degradation) (Reactome, 2026); Chondroitin Sulfate (CID 24766) (PubChem, NCBI, 2026) · Public domain; Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.