Role of glycine-534 and glycine-1179 of human multidrug resistance protein(MDR1) in drug-mediated control of ATP hydrolysis

The human multidrug resistance protein (MDR1) (P-glycoprotein), a member of the ATP-binding cassette (ABC) family. causes multidrug resistance by an a ctive transport mechanism. which keeps the intracellular level of hydrophob ic compounds below a cell-killing threshold. Human MDR1 variants with mutat ions affecting a conserved glycine residue within the ABC signature of eith er or both ABC units (G534D, G534V, G1179D and G534D/G1179D) were expressed and characterized in Spodoptera frugiperda (Sf9) cell membranes. These mut ations caused a loss of measurable ATPase activity but still allowed ATP bi nding and the formation of a transition-state intermediate (nucleotide trap ping). In contrast with the wild-type protein, in which substrate drugs acc elerate nucleotide trapping, in the ABC signature mutants nucleotide trappi ng was inhibited by MDR1-substrate drugs, suggesting a miscommunication bet ween the drug-binding site(s) and the catalytic domains. Equivalent mutatio ns of the two catalytic sites resulted in a similar effect, indicating the functional equivalence of the two sites. On the basis of these results and recent structural information on an ABC-ABC dimer [Hopfner, Karcher, Shin, Craig, Arthur, Carney and Tainer (2000) Cell 101, 759-800], we propose a ke y role of these glycine residues in the interdomain communication regulatin g drug-induced ATP hydrolysis.