Six-transmembrane helical domain 2 (TMD2) of P-glycoprotein 1 (Pgp) and related proteins
P-glycoprotein 1 (permeability glycoprotein, Pgp) also known as multidrug resistance protein 1 (MDR1) or ATP-binding cassette sub-family B member 1 (ABCB1) is a member of the superfamily of ATP-binding cassette (ABC) transporters. Pgp acts as an ATP-dependent efflux pump, binds drugs with diverse chemical structures and pump them out of the drug resistant cancer cells. It is responsible for decreased drug accumulation in multidrug-resistant cells and mediates the development of resistance to anticancer drugs. Pgp consists of two alpha-helical transmembrane domains (TMDs) and two cytoplasmic nucleotide-binding domains (NBDs). This protein also functions as a transporter in the blood-brain barrier. In addition to Pgp, breast cancer resistance protein (BCRP/MXR/ABC-P/ABCG2) and multidrug resistance-associated proteins (MRP1/ABCC1 and MRP2/ABCC2) function as drug efflux pumps of anticancer drugs, and overexpression of these transporters induces multidrug resistance to a broad spectrum of anticancer drugs including doxorubicin, taxol, and vinca alkaloids by actively pumping the drugs out of cells.
Comment:All members of this ABC transporter family contain 6 alpha-helices in each transmembrane domain (TMD) for a total of 12 TM segments in the complete transporter.
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