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#ABC transporter

8 public questions tagged with this topic.

Membrane Transportation

Which ABC transporter plays a role in cholesterol and phospholipid transport in hepatocytes?

Row labeled Q30 appears truncated but query addresses which ABC transporter handles cholesterol and phospholipid transport in hepatocytes. In canalicular membrane ABCB4 MDR3 is established phosphatidylcholine floppase essential for biliary phospholipid secretion, pairing with bile salt export via ABCB11 and cholesterol export via ABCG5/G8. Its ATP-driven flipping of phosphatidylcholine to outer leaflet allows bile acids to extract lipid into mixed micelles that solubilize cholesterol and buffer bile acid detergent toxicity. At sinusoidal membrane, ABCA1 effluxes cholesterol and phospholipid to

Ref: Borst et al., Annu Rev Biochem 2000, ABC transporters in lipid transport; Alberts, Chapter 11.

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Membrane Transportation

Which ABC transporter plays a role in cholesterol and phospholipid transport in hepatocytes?

Cholesterol and phospholipid homeostasis in hepatocytes involves coordinated action of several ABC transporters at canalicular membrane. ABCB4 MDR3 flips phosphatidylcholine from inner to outer leaflet making it available for bile salt extraction forming mixed micelles that protect biliary epithelium and solubilize cholesterol exported by ABCG5/G8 heterodimer. ABCB1 MDR1 primarily exports hydrophobic xenobiotics and drugs, not bulk phospholipid for bile formation, though it can translocate short-chain lipids in vitro. ABCA1, not listed among options but relevant, mediates phospholipid and chol

Ref: Oude Elferink & Paulusma 2007, Hepatic lipid transporters; Nicolaou et al., J Hepatol 2012.

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Membrane Transportation

The ABC transporter CFTR is unique because:

CFTR ABCC7 stands as atypical member of ABC superfamily because evolution transformed an active exporter scaffold into ATP-gated ion channel. Typical ABC exporters use ATP binding and hydrolysis to drive large TMD movements translocating substrate uphill. In CFTR, transmembrane domains create chloride-selective pore allowing passive flow down electrochemical gradient when open, while nucleotide-binding domains still bind ATP and regulate gating rather than transport solute stoichiometrically. Two ATP sites: NBD1 non-canonical hydrolyzes slowly, NBD2 drives channel closure upon hydrolysis. Addi

Ref: Gadsby et al., Nature 2006, Unique CFTR channel mechanism; Hwang & Sheppard, 2009.

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Membrane Transportation

Which ABC transporter is associated with multidrug resistance in cancer?

Cancer multidrug efflux is dominated not by CFTR or P-type ATPases but by ABC transporters that expel amphipathic chemotherapeutics from cytoplasm. ABCB1 P-glycoprotein MDR1 is best studied, overexpressed in colonic, renal, adrenocortical carcinomas and after chemotherapy induction in leukemia, lymphoma and breast cancer. Its polyspecific hydrophobic binding chamber accommodates doxorubicin, daunorubicin, vinblastine, vincristine, paclitaxel and etoposide causing cross-resistance. ABCC1 MRP1 exports glutathione conjugates of drugs, ABCG2 BCRP expels mitoxantrone and topotecan. Expression corre

Ref: Gottesman et al., Annu Rev Med 2002, MDR in cancer; Szakacs et al., Nat Rev Drug Discov 2006.

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Membrane Transportation

The ABC transporter in plants responsible for detoxification of xenobiotics is found in:

Plants lack animal Na+/K+ gradient but generate proton motive force via plasma membrane P-type H+-ATPase and vacuolar V-type H+-ATPase and pyrophosphatase, driving uptake and compartmentalization of metabolites. Detoxification of xenobiotics, herbicides, and endogenous secondary metabolites employs ATP-binding cassette transporters localized predominantly in vacuolar membrane tonoplast and plasma membrane. Vacuolar ABCC members often called MRP-like transport glutathione S-conjugates, phytochelatin heavy metal complexes, and glucuronide conjugates into vacuole for sequestration, reducing cytos

Ref: Martinoia et al., Planta 2002, Vacuolar transporters; Kang et al., PNAS 2011, ABC in detox.

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Membrane Transportation

Which ABC transporter is found in the liver and is responsible for phosphatidylcholine transport?

Hepatic bile secretion relies on coordinated action of several canalicular ABC transporters in hepatocytes. ABCB11 BSEP exports bile acids, ABCG5/ABCG8 heterodimer exports cholesterol, and ABCB4 previously called MDR2 in mice and MDR3 in humans is dedicated to phosphatidylcholine. ABCB4 acts as ATP-dependent floppase moving phosphatidylcholine from inner cytoplasmic leaflet to outer exoplasmic leaflet of canalicular membrane where bile salt micelles extract it into biliary space forming mixed micelles. This phospholipid shield protects cholangiocyte membranes from detergent attack by hydrophob

Ref: Oude Elferink & Paulusma, Pflugers Arch 2007, ABCB4 bile phospholipid secretion.

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Membrane Transportation

The ABC transporter superfamily is involved in:

ABC transporter superfamily represents large gene family with 48 members in humans associated with inherited disorders and drug resistance, present also in bacteria where many function as importers. Core architecture comprises two transmembrane domains typically six helices each forming substrate translocation chamber with diverse selectivity filters, and two nucleotide binding domains located cytoplasmically containing Walker A phosphate binding P-loop, Walker B magnesium coordination hhhhhD, signature C motif LSGGQ characteristic of ABC plus H-loop and Q-loop coordinating ATP. Transport cycl

Ref: Higgins, ABC Transporters Annual Review Cell Biol, Lipophilic Drug Export and MDR Phenotype.

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Membrane Transportation

What is the function of the ABC transporter superfamily?

ATP-binding cassette superfamily constitutes one of largest and most functionally diverse transporter groups present in all domains of life, with 48 members in human genome implicated in cystic fibrosis, Tangier disease and multidrug resistance. Each functional unit minimal consists of two transmembrane domains typically six helices each forming translocation pathway determining substrate specificity and two cytosolic nucleotide binding domains containing highly conserved Walker A P-loop GXXGXGKS binding phosphate, Walker B hhhhDE binding magnesium, signature motif LSGGQ unique to ABC, and Q-l

Ref: Dean et al., Genome Research, ABC Transporter Superfamily Substrates and Multidrug Resistance.

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