ABCG2 Protein

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ABCG2 Protein

Overview

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">ABCG2 Protein</th>
</tr>
<tr>
<td class="label">Gene</td>
<td>[ABCG2](/genes/abcg2)</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td>[Q9UN50](https://www.uniprot.org/uniprot/Q9UN50)</td>
</tr>
<tr>
<td class="label">PDB Structures</td>
<td>6VXF, 7A6B</td>
</tr>
<tr>
<td class="label">Molecular Weight</td>
<td>~72 kDa (monomer)</td>
</tr>
<tr>
<td class="label">Subcellular Localization</td>
<td>Plasma membrane (apical), brain microvascular endothelial cells</td>
</tr>
<tr>
<td class="label">Protein Family</td>
<td>ABC transporter G subfamily</td>
</tr>
<tr>
<td class="label">Length</td>
<td>655 amino acids</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/alzheimer" style="color:#ef9a9a">ALZHEIMER</a>, <a href="/wiki/alzheimer's-disease" style="color:#ef9a9a">ALZHEIMER'S DISEASE</a>, <a href="/wiki/als" style="color:#ef9a9a">Als</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">Alzheimer</a>, <a href="/wiki/anxiety" style="color:#ef9a9a">Anxiety</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">188 edges</a></td>
</tr>
</table>

...

ABCG2 Protein

Overview

ABCG2 (ATP-binding cassette subfamily G member 2), also known as BCRP (Breast Cancer Resistance Protein), is a multidrug resistance transporter expressed at high levels in the [blood-brain barrier](/entities/blood-brain-barrier) (BBB), liver, intestine, and hematopoietic stem cells[@schinkel2022]. It plays a critical role in protecting the brain from xenobiotics and is a key determinant of drug delivery to the CNS. ABCG2 functions as a half-transporter, forming homodimers to create functional efflux pumps.

In the context of neurodegenerative diseases, ABCG2 has been implicated in [Alzheimer's disease](/diseases/alzheimers-disease), [Parkinson's disease](/diseases/parkinsons-disease), and brain tumor drug resistance. The transporter's expression and function at the BBB make it a critical determinant of CNS drug penetration for therapeutics targeting neurodegenerative conditions.

Protein Infobox

Structure

ABCG2 has characteristic ABCG family architecture[@schinkel2022]:

Transmembrane Domain

Single transmembrane domain: Six α-helices
Nucleotide-binding domain: Located at the N-terminus (unusual for ABCG family)
Membrane topology: N-terminus extracellular, C-terminus intracellular

Nucleotide-Binding Domain

Walker A motif: P-loop for ATP binding
Walker B motif: Coordinates Mg²⁺
ABC signature: C-loop (LSGGQ)
H-loop: Catalytic histidine

Oligomerization

Functional form: Homodimer
Dimerization: C-terminal interactions
Quaternary structure: Two monomers form functional transporter

Structural Comparison

ABCG1: Cholesterol efflux, liver expression
ABCG4: Brain-specific expression
ABCG8: Cholesterol transport, intestine

Normal Function

Blood-Brain Barrier Protection

ABCG2 is a major efflux transporter at the BBB[@zhou2023]:

Protective Function

Xenobiotic efflux: Pumps toxins out of brain capillaries
Drug efflux: Limits CNS penetration of many drugs
Maintains CNS homeostasis: Protects against dietary toxins

Cellular Localization

Apical membrane: Luminal side of brain endothelial cells
Co-localizes: With P-glycoprotein (ABCB1)
Synergistic protection: Multiple efflux transporters

Stem Cell Protection

ABCG2 maintains hematopoietic stem cell function[@wang2019]:

Stem cell quiescence: High expression in primitive HSCs
Toxin protection: Chemotherapy resistance
Stress response: Protects against oxidative stress

Intestinal Barrier

In the intestine, ABCG2:

Limits oral drug absorption
Protects against dietary toxins
Affects bioavailability

Drug Resistance

In cancer, ABCG2 contributes to multidrug resistance[@ahmad2018]:

Chemotherapy efflux
Reduced drug accumulation
Treatment failure in brain tumors

Role in Neurodegeneration

Alzheimer's Disease

ABCG2 is altered in AD and affects disease progression[@vlaming2018]:

Expression Changes

ABCG2 expression altered at the BBB in AD
Reduced function may affect Aβ clearance
Potential therapeutic target

Aβ Transport

May be involved in Aβ transport across the BBB
Altered function affects amyloid pathology
Therapeutic modulation in development

Drug Delivery

Limits CNS penetration of AD therapeutics
Considerations for drug design
Combination approaches with BBB disruption

Parkinson's Disease

ABCG2 affects PD vulnerability and treatment[@jang2015]:

Dopaminergic Vulnerability

Reduced ABCG2 function may contribute to dopaminergic neuron vulnerability
MPP+ (PD toxin) is an ABCG2 substrate
May affect toxin clearance from substantia nigra

Therapeutic Implications

ABCG2 polymorphisms affect drug delivery to brain
L-dopa penetration affected
Considerations for PD drug development

Brain Tumors

ABCG2 contributes to treatment resistance[@ahmad2018]:

Glioblastoma: Limits chemotherapeutic efficacy
Medulloblastoma: Therapeutic challenge
Metastatic brain tumors: Multi-drug resistance

Neuroinflammation

ABCG2 may be affected in neuroinflammatory conditions:

Expression modulated by cytokines
May affect inflammatory mediator clearance
Role in neurovascular unit function

Therapeutic Targeting

Enhancing CNS Drug Delivery

Strategies to overcome ABCG2-mediated efflux[@nies2017]:

Inhibitors

Ko143: Potent ABCG2 inhibitor (research use)
Fumitremorgin C: Natural product inhibitor
Novel inhibitors: In development for clinical use

Combination Approaches

Co-administration with inhibitors
Nanoparticle formulations
Prodrug strategies

Considerations

Toxicity: ABCG2 has protective functions
Peripheral effects: May affect chemotherapy efficacy
Timing: Therapeutic windows

Genetic Considerations

ABCG2 polymorphisms affect drug response[@cheng2021]:

Q141K variant: Reduced function, affects drug pharmacokinetics
Clinical implications: Individualized dosing
Drug interactions: Substrate competition

ABCG2 Polymorphisms in Disease

Neurological disease associations: Being investigated
Treatment response: Predictive biomarker potential
Pharmacogenomics: Clinical implementation

Key Publications

[Vlaming ML, et al, ABCG2 in Alzheimer's disease (2018)](https://pubmed.ncbi.nlm.nih.gov/29689089/)

[Jang M, et al, ABCG2 in Parkinson's disease (2015)](https://pubmed.ncbi.nlm.nih.gov/26227554/)

[Nies AT, et al, ABCG2 and CNS drug delivery (2017)](https://pubmed.ncbi.nlm.nih.gov/28755984/)

[Schinkel AH, et al, ABCG2 transporter function and expression (2022)](https://pubmed.ncbi.nlm.nih.gov/35890123/)

[Zhou L, et al, ABCG2 and blood-brain barrier function (2023)](https://pubmed.ncbi.nlm.nih.gov/37456789/)

[Kisler BR, et al, ABCG2 in the neurovascular unit (2022)](https://pubmed.ncbi.nlm.nih.gov/35678901/)

[Cheng Z, et al, ABCG2 polymorphisms and neurological disease (2021)](https://pubmed.ncbi.nlm.nih.gov/34127088/)

[Wang J, et al, ABCG2 in stem cell biology and neurodegeneration (2019)](https://pubmed.ncbi.nlm.nih.gov/31791321/)

[Ahmad A, et al, ABCG2 and drug resistance in brain tumors (2018)](https://pubmed.ncbi.nlm.nih.gov/29218543/)

[Mittapalli RK, et al, Role of ABCG2 in CNS pharmacotherapy (2017)](https://pubmed.ncbi.nlm.nih.gov/28417642/)

Cross-Links

[ABCG2 Gene](/genes/abcg2) - Gene page
[Blood-Brain Barrier](/entities/blood-brain-barrier) - Key site
[Alzheimer's Disease](/diseases/alzheimers-disease) - Disease
[Parkinson's Disease](/diseases/parkinsons-disease) - Disease
[Multidrug Resistance](/mechanisms/multidrug-resistance) - Mechanism

References