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The Effect of the Lipid Environment on Drug Binding and Transport by the P‐Glycoprotein Multidrug Transporter
Author(s) -
Sharom Frances Jane,
Clay Adam T.
Publication year - 2012
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.26.1_supplement.603.1
Subject(s) - chemistry , lipid bilayer , atp binding cassette transporter , p glycoprotein , transporter , multiple drug resistance , membrane , lipophilicity , partition coefficient , biochemistry , atp hydrolysis , biophysics , enzyme , chromatography , biology , atpase , gene , antibiotics
The P‐glycoprotein multidrug transporter (Pgp, ABCB1) is an ABC protein that effluxes hundreds of structurally unrelated compounds from cells, and is implicated in multidrug resistance in many human cancers. The membrane environment is critically important for Pgp function since lipophilic substrates partition into, and are pumped out of, the membrane. Using purified Pgp reconstituted into proteoliposomes of defined lipids, the effect of the bilayer melting transition on the lipid partition coefficient, binding affinity, and initial rate of transport was measured for Hoechst 33342, LDS‐751 and MK‐571. All drugs partitioned best into liquid crystalline lipid, and bound to Pgp with millimolar affinities within the membrane, suggesting that they interact with the protein weakly. Pgp drug binding affinity was modulated by both the lipid phase state and acyl chain length, and was higher for all drugs in the rigid gel phase. The k cat values for Pgp‐mediated drug transport were also sensitive to lipid melting, however, they were higher in the liquid crystalline phase. Transition state analysis showed the existence of entropy‐enthalpy compensation and an isokinetic relationship between ΔH ‡ and ΔS ‡ . The transport rate is proposed to be controlled by the drug binding affinity and a large conformational change, rather than the rate of ATP hydrolysis. This research is funded by the Canadian Cancer Society (grant #700248).