The ATP-binding cassette subfamily B member 1 (ABCB1), also known as P-glycoprotein (P-gp) or multidrug resistance protein 1 (MDR1), is a critical efflux transporter that plays a fundamental role in protecting the brain from xenobiotics and maintaining drug pharmacokinetics[@juliano1976]. Encoded by the ABCB1 gene, this 170 kDa transmembrane protein utilizes ATP hydrolysis to actively extrude a wide range of substrates across cellular membranes[@ambudkar1999].
The ATP-binding cassette subfamily B member 1 (ABCB1), also known as P-glycoprotein (P-gp) or multidrug resistance protein 1 (MDR1), is a critical efflux transporter that plays a fundamental role in protecting the brain from xenobiotics and maintaining drug pharmacokinetics[@juliano1976]. Encoded by the ABCB1 gene, this 170 kDa transmembrane protein utilizes ATP hydrolysis to actively extrude a wide range of substrates across cellular membranes[@ambudkar1999].
Structure
ABCB1 is composed of two transmembrane domains (TMDs), each containing six transmembrane helices, and two nucleotide-binding domains (NBDs) that hydrolyze ATP to drive substrate translocation[@loo2014]. The protein adopts an inward-facing conformation in the absence of substrate and undergoes dramatic conformational changes to an outward-facing state during the transport cycle[@locher2004]. Key structural features include:
Transmembrane Domain: 12 transmembrane helices forming the substrate translocation pore
Nucleotide-Binding Domains: Two NBDs that dimerize upon ATP binding to power the transport mechanism
Drug-Binding Pocket: Large, flexible internal cavity capable of accommodating diverse hydrophobic substrates
Linker Region: Intracellular connecting region between TMDs and NBDs
Normal Function
Blood-Brain Barrier Protection
ABCB1 is highly expressed on the apical (luminal) surface of brain microvascular endothelial cells forming the [blood-brain barrier](/entities/blood-brain-barrier) (BBB)[@abbott2010]. Here, it functions as a gatekeeper, preventing the accumulation of potentially neurotoxic compounds in the central nervous system:
Xenobiotic Efflux: Actively pumps out drugs, toxins, and metabolites from the brain capillary endothelium back into the bloodstream
Endogenous Substrate Transport: Handles certain steroid hormones, cytokines, and lipid metabolites
BBB Integrity Maintenance: Contributes to maintaining the tight junction integrity of the BBB
Physiological Roles
Beyond the BBB, ABCB1 is expressed in various tissues:
Liver: Canalicular membrane of hepatocytes for bile secretion
Kidney: Proximal tubule apical membrane for drug excretion
Intestine: Apical enterocyte membrane limiting oral drug absorption
Testis: Blood-testis barrier protection
Placenta: Fetal protection from maternal drugs
Role in Neurodegeneration
Alzheimer's Disease
ABCB1 plays complex roles in Alzheimer's disease pathogenesis:
Amyloid Clearance: May facilitate [Aβ](/proteins/amyloid-beta) transport across the BBB; ABCB1 polymorphisms affect Aβ brain accumulation[@vogelgesang2002]
Drug Efflux: Altered ABCB1 function in AD patients may affect therapeutic drug delivery to the brain
Inflammation Interaction: ABCB1 dysfunction may exacerbate neuroinflammation by impairing immune cell trafficking
Parkinson's Disease
MPP+ Toxicity: ABCB1 can efflux the neurotoxin MPP+, which is taken up by dopamine [neurons](/entities/neurons)[@cheng2012]
L-DOPA Transport: May influence L-DOPA brain pharmacokinetics
[Alpha-Synuclein](/proteins/alpha-synuclein): Evidence suggests ABCB1 may affect α-synuclein aggregation dynamics
ALS and FTD
[C9orf72](/entities/c9orf72) DPR Transport: Potential role in transporting dipeptide repeat proteins
Drug Delivery Challenges: ABCB1 overexpression in ALS may limit therapeutic efficacy
[Juliano RL, Ling V, A surface glycoprotein modulating drug permeability in Chinese hamster ovary cell mutants (1976)](https://doi.org/10.1016/0005-2736(76)
[Ambudkar SV, Dey S, Hrycyna CA, Ramachandra M, Pastan I, Gottesman MM, Biochemical, cellular, and pharmacological aspects of the multidrug transporter (1999)](https://doi.org/10.1146/annurev.pharmtox.39.1.361)
[Loo TW, Clarke DM, Recent progress in understanding the mechanism of P-glycoprotein ATP hydrolysis (2014)](https://doi.org/10.1007/s00232-014-9710-8)
[Locher KP, Structure and mechanism of ATP-binding cassette (ABC) transporters (2004)](https://doi.org/10.1146/annurev.biochem.73.011303.073626)
[Abbott NJ, Patabendige AA, Dolman DE, Yusof SR, Begley DJ, Structure and function of the blood-brain barrier (2010)](https://doi.org/10.1016/j.nbd.2009.07.030)
[Vogelgesang S, Cascorbi I, Schroeder E, et al, Deposition of Alzheimer's beta-amyloid is inversely correlated with P-glycoprotein expression in the brains of elderly non-demented humans (2002)](https://doi.org/10.1097/00008571-200210000-00005)
[Cheng SB, Nakata K, Kuma A, Ohta S, The function of P-glycoprotein in the black worm (Lumbriculus variegatus) against 1-methyl-4-phenylpyridinium (MPP+) (2012)](https://doi.org/10.1016/j.neuint.2011.12.008)