Abstract
ATP-Binding Cassette (ABC) transporters are efflux pumps frequently associated with multidrug resistance in many biological systems, including malaria. Antimalarial drug-resistance involves an ABC transporter, PfMDR1, a homologue of P-glycoprotein in humans. Twenty years of research have shown that several single nucleotide polymorphisms in pfmdr1 modulate in vivo and/or in vitro drug susceptibility. The underlying physiological mechanism of the effect of these mutations remains unclear. Here we develop structural models for PfMDR1 in different predicted conformations, enabling the study of transporter motion. Such analysis of functional polymorphisms allows determination of their potential role in transport and resistance. The bacterial MsbA ABC pump is a PfMDR1 homologue. MsbA crystals in different conformations were used to create PfMDR1 models with Modeller software. Sequences were aligned with ClustalW and analysed by Ali2D revealing a high level of secondary structure conservation. To validate a potential drug binding pocket we performed antimalarial docking simulations. Using aminoquinoline as probe drugs in PfMDR1 mutated parasites we evaluated the physiology underlying the mechanisms of resistance mediated by PfMDR1 polymorphisms. We focused on the analysis of well known functional polymorphisms in PfMDR1 amino acid residues 86, 184, 1034, 1042 and 1246. Our structural analysis suggested the existence of two different biophysical mechanisms of PfMDR1 drug resistance modulation. Polymorphisms in residues 86/184/1246 act by internal allosteric modulation and residues 1034 and 1042 interact directly in a drug pocket. Parasites containing mutated PfMDR1 variants had a significant altered aminoquinoline susceptibility that appears to be dependent on the aminoquinoline lipophobicity characteristics as well as vacuolar efflux by PfCRT. We previously described the in vivo selection of PfMDR1 polymorphisms under antimalarial drug pressure. Now, together with recent PfMDR1 functional reports, we contribute to the understanding of the specific structural role of these polymorphisms in parasite antimalarial drug response.
Highlights
Efforts to control Plasmodium falciparum malaria are currently reliant on vector control and chemotherapy
In the present work we propose a model for PfMDR1 structure and motion during transport
The existence of extensive literature describing the functional and molecular epidemiologic impact of polymorphisms in this transporter together with knowledge of the structure of ATP-Binding Cassette (ABC) transporters, made it possible to predict the functional role of mutant residues in PfMDR1
Summary
Efforts to control Plasmodium falciparum malaria are currently reliant on vector control and chemotherapy. A cornerstone event in malaria chemotherapy occurred in Thailand, during the 1990s: the recovery of the efficacy of mefloquine (MQ) through its combination with artesunate [4,5]. Following this successful implementation, conceptually similar artemisinin derivative combination therapies (ACT) were progressively adopted worldwide. Recent reports have provided the first indications that resistance to ACTs may be emerging in natural parasite populations [9,10] If such resistance spreads widely, our drug-based efforts to control malaria will be severely held back
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