Detergents as intrinsic P-glycoprotein substrates and inhibitors.
We assessed the interaction of three electrically neutral detergents (Triton X-100, C(12)EO(8), and Tween 80) with P-glycoprotein (ABCB1, MDR1) and identified the molecular elements responsible for this interaction. To this purpose we titrated P-glycoprotein in inside-out plasma membrane vesicles of MDR1-transfected mouse embryo fibroblasts (NIH-MDR1-G185) with the detergents below their critical micelle concentration, CMC. The P-glycoprotein ATPase measured as a function of the detergent concentration yielded bell-shaped activity curves which were evaluated with a two-site binding model. The lipid-water partition coefficient and the transporter-water binding constant of the detergents were measured independently. Knowledge of these two parameters allowed assessment of the free energy of detergent binding to P-glycoprotein in the lipid membrane, DeltaG(tl)(0), that reflects the direct detergent-transporter affinity. It increased as the number of ethoxyl groups increased, suggesting that these hydrogen bond acceptor groups are the key elements for the detergent-transporter interaction in the lipid membrane. The free energy of binding to P-glycoprotein per ethoxyl group (EO) was determined as approximately DeltaG(EO)(0)=-1.6 kJ/mol. The present findings moreover document that, depending on the concentration applied, detergents are intrinsic substrates for, or inhibitors of P-glycoprotein.
Li-Blatter
Xiaochun
X
Biophysical Chemistry, Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland.
Nervi
Pierluigi
P
Seelig
Anna
A
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000737:chemistry* / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D001692:Biological Transport; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology; D003902:Detergents / Q000494:pharmacology*; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D007700:Kinetics; D008563:Membrane Lipids / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D008823:Micelles; D014700:Verapamil / Q000494:pharmacology
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D003902:Detergents; D004791:Enzyme Inhibitors; D008563:Membrane Lipids; D008823:Micelles; D016572:Cyclosporine; D014700:Verapamil; D000251:Adenosine Triphosphatases