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

# LDL receptor

The LDL receptor pulls LDL particles out of the blood into the cell; when it fails, LDL cholesterol is high from birth.

Updated 2026-11-01

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## Key facts

- It recognises ApoB-100 on LDL and ApoE on IDL and remnants.
- Receptor-mediated endocytosis in clathrin-coated pits; in the acidic endosome it releases LDL and returns to the membrane.
- The liver carries most receptors and clears most plasma LDL.
- SREBP-2 switches its gene on when the cell lacks cholesterol; PCSK9 sends it for degradation.
- LDLR variants are the most common cause of familial hypercholesterolaemia.

**Also called**
LDLR

**Genes**
LDLR

**Structure (PDB)**
[1N7D](https://www.rcsb.org/structure/1N7D)

## Structure

- An 860-residue protein: ligand-binding domain (cysteine-rich repeats that bind calcium), EGF-precursor-like domain, glycosylated region, transmembrane segment and a cytoplasmic tail with the NPxY signal.
- Structure 1N7D shows the extracellular domain at acidic pH, folded back on itself: this is how it lets go of LDL in the endosome.

## Regulation

- SREBP-2 raises its transcription when cell cholesterol falls.
- PCSK9 binds its EGF-A domain and stops it recycling: it is degraded in the lysosome.
- IDOL, an LXR-induced ubiquitin ligase, also degrades it.

## Inhibitors and toxins

- Not a direct target: statins, ezetimibe and PCSK9 inhibitors increase its numbers.

## Clinical notes

- With one faulty copy LDL is often doubled; with two it can be four or more times normal and cause heart attacks in childhood.
- Statins and PCSK9 inhibitors work through the receptor: with no functional receptors the response is poor.
- Hypothyroidism reduces LDL receptors and raises cholesterol.

## Related conditions

- [Familial hypercholesterolemia](https://durgical.com/en/conditions/familial-hypercholesterolemia/)
- [Atherosclerosis and dyslipidaemia](https://durgical.com/en/conditions/atherosclerosis-and-dyslipidaemia/)
- [Myocardial Infarction (Heart Attack)](https://durgical.com/en/conditions/myocardial-infarction/)
- [Hypothyroidism](https://durgical.com/en/conditions/hypothyroidism/)

## Related

- [LDL (low-density lipoprotein)](https://durgical.com/en/biochemistry/topics/ldl/)
- [PCSK9](https://durgical.com/en/biochemistry/enzymes/pcsk9/)
- [Apolipoprotein B (ApoB-100 and ApoB-48)](https://durgical.com/en/biochemistry/enzymes/apolipoprotein-b/)
- [Apolipoprotein E (ApoE)](https://durgical.com/en/biochemistry/enzymes/apolipoprotein-e/)
- [Lipoprotein metabolism](https://durgical.com/en/biochemistry/topics/lipoprotein-metabolism/)
- [HMG-CoA reductase](https://durgical.com/en/biochemistry/enzymes/hmg-coa-reductase/)

## Test yourself

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

## Which apolipoproteins does the LDL receptor recognise?

ApoB-100 (LDL) and ApoE (IDL and remnants); ApoB-48 does not bind it.

## Why does a statin increase liver LDL receptors?

Lower ER cholesterol activates SREBP-2, which induces the LDLR gene.

## What happens to the receptor when PCSK9 binds it?

It is internalised with LDL but does not recycle: it is degraded in the lysosome.

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

Sources: [LDLR: Low-density lipoprotein receptor (human)](https://rest.uniprot.org/uniprotkb/P01130.txt) (UniProt, 2026); [LDLR gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/ldlr/) (MedlinePlus, US National Library of Medicine, 2026); [LDL clearance (R-HSA-8964038)](https://reactome.org/PathwayBrowser/#/R-HSA-8964038) (Reactome, 2026); [1N7D: Extracellular domain of the LDL receptor](https://www.rcsb.org/structure/1N7D) (RCSB Protein Data Bank, 2026); [UniProt P01130: variants](https://www.uniprot.org/uniprotkb/P01130/entry) (UniProt, 2026).

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Representative model, for educational purposes only.

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