Resistance mutations reveal the atovaquone‐binding domain of cytochrome b in malaria parasites

Abstract

Atovaquone represents a class of antimicrobial agents with a broad‐spectrum activity against various parasitic infections, including malaria, toxoplasmosis and Pneumocystis pneumonia. In malaria parasites, atovaquone inhibits mitochondrial electron transport at the level of the cytochrome bc1 complex and collapses mitochondrial membrane potential. In addition, this drug is unique in being selectively toxic to parasite mitochondria without affecting the host mitochondrial functions. A better understanding of the structural basis for the selective toxicity of atovaquone could help in designing drugs against infections caused by mitochondria‐containing parasites. To that end, we derived nine independent atovaquone‐resistant malaria parasite lines by suboptimal treatment of mice infected with Plasmodium yoelii; these mutants exhibited resistance to atovaquone‐mediated collapse of mitochondrial membrane potential as well as inhibition of electron transport. The mutants were also resistant to the synergistic effects of atovaquone/ proguanil combination. Sequencing of the mitochondrially encoded cytochrome b gene placed these mutants into four categories, three with single amino acid changes and one with two adjacent amino acid changes. Of the 12 nucleotide changes seen in the nine independently derived mutants 11 replaced A:T basepairs with G:C basepairs, possibly because of reactive oxygen species resulting from atovaquone treatment. Visualization of the resistance‐conferring amino acid positions on the recently solved crystal structure of the vertebrate cytochrome bc1 complex revealed a discrete cavity in which subtle variations in hydrophobicity and volume of the amino acid side‐chains may determine atovaquone‐binding affinity, and thereby selective toxicity. These structural insights may prove useful in designing agents that selectively affect cytochrome bc1 functions in a wide range of eukaryotic pathogens.

Molecular Surveillance as Monitoring Tool for Drug-Resistant Plasmodium falciparum in Suriname

“…[1][2][3][4] CQ resistance in vitro and in vivo is associated with mutations in the P. falciparum CQ resistance transporter gene ( pfcrt gene), which encodes a putative transporter localized in the parasite's digestive vacuole. One particular mutation at position 76 ( pfcrtK76T), causing the amino acid substitution (Lysine !…”

Antimalarial 4(1H)-pyridones bind to the Q i site of cytochrome bc 1

“…Several mutations, giving rise to atovaquone-resistant strains of P. falciparum and Toxoplasma gondii, have been reported since the turn of the century (23)(24)(25)(26)(27). These mutations arise in the Q o pocket and prevent atovaquone from binding (28).…”

Structural Plasticity of Malaria Dihydroorotate Dehydrogenase Allows Selective Binding of Diverse Chemical Scaffolds

“…Interestingly, despite a vast number of ongoing attempts, PfDHODH represents one of only a few truly new targets for the development of anti-malarial agents since the discovery that atovoquone targets the cytochrome bc 1 complex in the mitochondria (20). This has led to a substantial effort to target PfDHODH for drug discovery programs and to the identification of diverse scaffolds showing species-selective inhibition of the enzyme (17,18,(21)(22)(23)(24).…”