[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Biochemistry](https://durgical.com/en/biochemistry/) › Apolipoprotein E (ApoE)

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

# Apolipoprotein E (ApoE)

ApoE is the key that lets chylomicron remnants and IDL into the liver; its variants change cholesterol and Alzheimer risk.

Updated 2026-11-01

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## Key facts

- It is on chylomicrons, remnants, VLDL, IDL and some HDL; HDL hands it to new particles.
- It binds the LDL receptor and liver LRP1 to clear remnants.
- Three common alleles: ε2, ε3 (most frequent) and ε4; they differ at residues 112 and 158.
- ApoE2 binds receptors poorly: ε2/ε2 plus a second factor causes dysbetalipoproteinaemia (type III).
- ApoE4 is the main genetic risk factor for late-onset Alzheimer disease.

**Also called**
ApoE

**Genes**
APOE

**Structure (PDB)**
[1NFN](https://www.rcsb.org/structure/1NFN)

## Structure

- A mature 299-residue protein: a four-helix N-terminal domain that binds the receptor (region 136–150) and a lipid-binding C-terminal domain.
- Structure 1NFN is the ApoE3 N-terminal domain: a four-helix bundle.

## Regulation

- It is made mainly by the liver, and also by brain astrocytes and macrophages.
- LXR (activated by oxysterols) raises its expression in macrophages.

## Inhibitors and toxins

- Not the target of any approved drug.

## Clinical notes

- ε2/ε2 plus obesity, diabetes or hypothyroidism: high remnants, palmar xanthomas and early atherosclerosis.
- ε4 is linked to slightly higher LDL and Alzheimer disease; ε2 to lower Alzheimer risk.
- APOE genotyping helps confirm dysbetalipoproteinaemia.

## Related conditions

- [Familial dysbetalipoproteinemia (type III hyperlipoproteinemia)](https://durgical.com/en/conditions/familial-dysbetalipoproteinemia/)
- [Alzheimer disease](https://durgical.com/en/conditions/alzheimer-disease/)
- [Atherosclerosis and dyslipidaemia](https://durgical.com/en/conditions/atherosclerosis-and-dyslipidaemia/)

## Related

- [Chylomicron](https://durgical.com/en/biochemistry/topics/chylomicron/)
- [VLDL (very-low-density lipoprotein)](https://durgical.com/en/biochemistry/topics/vldl/)
- [HDL (high-density lipoprotein)](https://durgical.com/en/biochemistry/topics/hdl/)
- [LDL receptor](https://durgical.com/en/biochemistry/enzymes/ldl-receptor/)
- [Lipoprotein metabolism](https://durgical.com/en/biochemistry/topics/lipoprotein-metabolism/)

## Test yourself

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

## What does ApoE do on chylomicron remnants?

It is the ligand that binds them to the liver LDL receptor and LRP1 so they are cleared.

## Which APOE genotype is linked to dysbetalipoproteinaemia?

ε2/ε2, almost always with a second factor such as obesity, diabetes or hypothyroidism.

## Which APOE allele raises the risk of late-onset Alzheimer disease?

ε4.

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

Sources: [APOE: Apolipoprotein E (human)](https://rest.uniprot.org/uniprotkb/P02649.txt) (UniProt, 2026); [APOE gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/apoe/) (MedlinePlus, US National Library of Medicine, 2026); [1NFN: APOLIPOPROTEIN E3 (APOE3)](https://www.rcsb.org/structure/1NFN) (RCSB Protein Data Bank, 2026); [Familial dysbetalipoproteinemia: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000402.htm) (MedlinePlus, US National Library of Medicine, 2026).

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Representative model, for educational purposes only.

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