Biochemistry · Protein
Apolipoprotein B (ApoB-100 and ApoB-48) !
ApoB is the structural protein of chylomicrons, VLDL, IDL and LDL: each of these particles carries a single copy.
Updated 2026-11-01
Key facts
- One gene gives two proteins: ApoB-100 in the liver and ApoB-48 in the gut, through mRNA editing (APOBEC-1 creates a stop codon).
- ApoB-48 (48% of the length) builds chylomicrons; ApoB-100 builds VLDL, IDL and LDL.
- Only ApoB-100 has the domain that binds the LDL receptor.
- To form a particle it needs MTP, which loads it with lipid in the ER.
- One atherogenic particle carries one ApoB: measuring ApoB counts the particles.
- Also called
- ApoB
- Genes
- APOB
Structure
- ApoB-100 is huge (4,563 residues, about 515 kDa) and non-exchangeable: it stays on the particle for life.
- It wraps the particle like a belt; there is no complete crystal structure.
Regulation
- It is made continuously; what is regulated is how much is degraded before secretion, depending on available lipid and insulin.
Inhibitors and toxins
- Lomitapide inhibits MTP and slows secretion of ApoB particles
- Mipomersen, an antisense oligonucleotide against APOB mRNA (withdrawn in many countries)
Clinical notes
- APOB variants that impair receptor binding (such as Arg3500Gln) cause familial hypercholesterolaemia (familial defective ApoB).
- Truncating variants cause familial hypobetalipoproteinaemia; loss of MTP causes abetalipoproteinaemia.
- ApoB and non-HDL cholesterol estimate risk better when triglycerides are high or in diabetes.
Related conditions
- Familial hypercholesterolemia
- Abetalipoproteinemia (Bassen–Kornzweig syndrome)
- Atherosclerosis and dyslipidaemia
Related
- LDL (low-density lipoprotein)
- VLDL (very-low-density lipoprotein)
- Chylomicron
- LDL receptor
- Lipoprotein metabolism
Test yourself
Think of the answer, then tap the question to see it.
How do two proteins, ApoB-100 and ApoB-48, come from one gene?
In the gut, APOBEC-1 edits the mRNA and creates a stop codon: the protein ends at 48% of its length.
Why are chylomicron remnants not taken up via ApoB-48?
ApoB-48 lacks the LDL receptor-binding domain; remnants enter via ApoE.
What does blood ApoB measure?
The number of atherogenic particles, since each VLDL, IDL, LDL or Lp(a) carries one ApoB.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: APOB: Apolipoprotein B-100 (human) (UniProt, 2026); APOB gene: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); MTTP gene: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); Chylomicron assembly (R-HSA-8963888) (Reactome, 2026).
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Representative model, for educational purposes only.