| Abstract
| - Recently, mutations in the novel polytopic integral membrane protein PfCRT were shown tocause chloroquine resistance (CQR) in the malarial parasite Plasmodium falciparum. PfCRT is not amember of the well-known family of ABC proteins that have previously been associated with other drugresistance phenomena. Thus, the mechanism(s) whereby mutant PfCRT molecules confer antimalarialdrug resistance is (are) unknown. Previously, we succeeded in overexpressing PfCRT to high levels inPichia pastoris yeast by synthesizing a codon-optimized version of the pfcrt gene. Using purified membranesand inside-out plasma membrane vesicles (ISOV) isolated from strains harboring either wild-type or CQR-associated mutant PfCRT, we now show that under deenergized conditions the PfCRT protein specificallybinds the antimalarial drug chloroquine (CQ) with a KD near 400 nM but does not measurably bind therelated drug quinine (QN) at physiologically relevant concentrations. Transport studies using ISOV showthat QN is passively accumulated as expected on the basis of previous measurement of the ISOV ΔpHfor the different strains. However, passive accumulation of CQ is lower than expected for ISOV harboringmutant PfCRT, despite higher ΔpH for these ISOV.
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