bMalaria's ability to rapidly adapt to new drugs has allowed it to remain one of the most devastating infectious diseases of humans. Understanding and tracking the genetic basis of these adaptations are critical to the success of treatment and intervention strategies. The novel antimalarial resistance locus PF10_0355 (Pfmspdbl2) was previously associated with the parasite response to halofantrine, and functional validation confirmed that overexpression of this gene lowered parasite sensitivity to both halofantrine and the structurally related antimalarials mefloquine and lumefantrine, predominantly through copy number variation. Here we further characterize the role of Pfmspdbl2 in mediating the antimalarial drug response of Plasmodium falciparum. Knockout of Pfmspdbl2 increased parasite sensitivity to halofantrine, mefloquine, and lumefantrine but not to unrelated antimalarials, further suggesting that this gene mediates the parasite response to a specific class of antimalarial drugs. A single nucleotide polymorphism encoding a C591S mutation within Pfmspdbl2 had the strongest association with halofantrine sensitivity and showed a high derived allele frequency among Senegalese parasites. Transgenic parasites expressing the ancestral Pfmspdbl2 allele were more sensitive to halofantrine and structurally related antimalarials than were parasites expressing the derived allele, revealing an allele-specific effect on drug sensitivity in the absence of copy number effects. Finally, growth competition experiments showed that under drug pressure, parasites expressing the derived allele of Pfmspdbl2 outcompeted parasites expressing the ancestral allele within a few generations. Together, these experiments demonstrate that modulation of Pfmspdbl2 affects malaria parasite responses to antimalarial drugs.
Malaria drug resistance poses a serious threat to treatment and control efforts (1, 2). Loci such as pfcrt, dhfr, and pfmdr1 are all known to play a role in mediating Plasmodium falciparum drug resistance and can do so through mutations or copy number variation (CNV) (3), but the precise mechanisms of resistance to many antimalarial drugs are poorly understood. Additionally, these well-known loci do not fully explain the range of responses observed in resistant parasites, suggesting that other loci may be involved in mediating parasite drug sensitivity (4, 5).Pfmspdbl2, also called PF10_0355, PF3D7_1036300, and MSP3.8, is a novel antimalarial resistance locus recently identified in a genome-wide association study (GWAS) of 50 global parasite isolates with a high-density single nucleotide polymorphism (SNP) array (6). CNV was also observed at this locus among natural parasite isolates, and parasites with more than one copy of Pfmspdbl2 tended to be more resistant to halofantrine. Overexpression of either the sensitive or the resistant allele of Pfmspdbl2 made parasites less sensitive to halofantrine, mefloquine, and lumefantrine but not to structurally unrelated antimalarials. This validated Pfmspdbl2 as a novel antimalaria...