Biochemistry · Enzyme
α-L-Iduronidase !
α-L-Iduronidase removes iduronic acid from the end of dermatan and heparan sulfate in the lysosome. Its absence causes mucopolysaccharidosis I (Hurler).
Updated 2026-11-01
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Key facts
- It hydrolyses the terminal (unsulfated) α-L-iduronic acid of dermatan sulfate and heparan sulfate.
- It acts right after iduronate 2-sulfatase (IDS gene), which first removes the sulfate; that enzyme is missing in Hunter syndrome.
- IDUA gene (4p16.3); autosomal recessive inheritance.
- Without it, both GAGs build up in lysosomes and spill into urine.
Regulation
- Active at acid pH.
- Reaches the lysosome tagged with mannose 6-phosphate; neighbouring cells can take up the secreted enzyme (cross-correction).
Inhibitors and toxins
- Iduronic acid analogues (laboratory iminosugars, such as the one in PDB 4KGL)
Clinical notes
- Severe MPS I (Hurler): coarse features, corneal clouding, lumbar gibbus, hepatosplenomegaly, valve disease and cognitive decline.
- Attenuated MPS I (Hurler–Scheie, Scheie): stiff joints, corneal clouding and valve disease with normal or near-normal intelligence.
- Haematopoietic stem cell transplant before age two also delivers enzyme to the brain; intravenous replacement treats organs and joints.
Related conditions
Related
- Glycosaminoglycans (mucopolysaccharides)
- Lysosomal storage diseases
- Mannose 6-phosphate tagging (sending enzymes to the lysosome)
Test yourself
Think of the answer, then tap the question to see it.
Which enzyme acts just before α-L-iduronidase in dermatan sulfate breakdown?
Iduronate 2-sulfatase, which removes the sulfate; it fails in Hunter syndrome.
What is cross-correction?
A healthy cell secretes enzyme carrying mannose 6-phosphate and a sick cell takes it up by its receptor; this underlies transplant and replacement.
Which GAGs build up when α-L-iduronidase is missing?
Dermatan sulfate and heparan sulfate.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: IDUA: Alpha-L-iduronidase (human) (UniProt, 2026); IDUA gene: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); 4OBR: Crystal structure of human alpha-L-iduronidase complex with alpha-L-iduronic acid (RCSB Protein Data Bank, 2026); MPS I - Hurler syndrome (HS-GAG degradation) (Reactome, 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.