FUNCTIONAL EXPRESSION OF MOUSE MDR1 IN ESCHERICHIA-COLI

We describe functional expression of the mouse multidrug-resistance pr otein (P-glycoprotein; P-gp) in an Escherichia coli mutant defective i n the outer membrane protease ompT. Heterologously expressed mdr1 appe ars as an unglycosylated species with an apparent molecular mass of 14 0 kDa in the membrane of the mutant. Unglycosylated mdr1 retains the a bility to bind the photoactivatable drug analog [I-125]iodoarylazidopr azosin and confers resistance to tetraphenylphosphonium (TPP+) and tet raphenylarsonium (TPA+), known mdr1 substrates. In vivo resistance is linked to reduced cellular accumulation and energy-dependent efflux of the lipophilic cations. Surprisingly, discrete mutations in the predi cted nucleotide binding folds of mdr1 that abolish drug resistance in mammalian cells have no apparent effect on TPA+ efflux via mdr1 in E. coli.