Complex Endosymbioses II: The Nonphotosynthetic Plastid of Apicomplexa Parasites (The Apicoplast) and Its Integrated Metabolism

International audienceChloroplasts are essential organelles that are responsible for photosynthesis in a wide range of organisms that have colonized all biotopes on Earth such as plants and unicellular algae. Interestingly, a secondary endosymbiotic event of a red algal ancestor gave rise to a group of organisms that have adopted an obligate parasitic lifestyle named Apicomplexa parasites. Apicomplexa parasites are some of the most widespread and poorly controlled pathogens in the world. These infectious agents are responsible for major human diseases such as toxoplasmosis, caused by Toxoplasma gondii, and malaria caused by Plasmodium spp. Most of these parasites harbor this relict plastid named the apicoplast, which is essential for parasite survival. The apicoplast has lost photosynthetic capacities but are metabolically similar to plant and algal chloroplasts. The apicoplast is considered a novel and important drug target against Apicomplexa parasites. This chapter focuses on the apicoplast of apicomplexa parasites, its maintenance, and its metabolic pathways

Consistent signatures of selection from genomic analysis of pairs of temporal and spatial Plasmodium falciparum populations from The Gambia

Genome sequences of 247 Plasmodium falciparum isolates collected in The Gambia in 2008 and 2014 were analysed to identify changes possibly related to the scale-up of antimalarial interventions that occurred during this period. Overall, there were 15 regions across the genomes with signatures of positive selection. Five of these were sweeps around known drug resistance and antigenic loci. Signatures at antigenic loci such as thrombospodin related adhesive protein (Pftrap) were most frequent in eastern Gambia, where parasite prevalence and transmission remain high. There was a strong temporal differentiation at a non-synonymous SNP in a cysteine desulfarase (Pfnfs) involved in iron-sulphur complex biogenesis. During the 7-year period, the frequency of the lysine variant at codon 65 (Pfnfs-Q65K) increased by 22% (10% to 32%) in the Greater Banjul area. Between 2014 and 2015, the frequency of this variant increased by 6% (20% to 26%) in eastern Gambia. IC50 for lumefantrine was significantly higher in Pfnfs-65K isolates. This is probably the first evidence of directional selection on Pfnfs or linked loci by lumefantrine. Given the declining malaria transmission, the consequent loss of population immunity, and sustained drug pressure, it is important to monitor Gambian P. falciparum populations for further signs of adaptation

Road towards development of new antimalarial: organelle associated metabolic pathways in Plasmodium as drug targets and discovery of lead drug candidates

Malaria remains a global threat with millions of deaths annually. Emergence of parasite strains resistant to widely used antimalarials, including the artemisinin combination therapy (ACT), and the absence of an effective vaccine makes treatment of malaria difficult than ever before. The need of the hour is to re-evaluate the chemotherapeutic approach and to identify new drug targets and develop new pharmacophores against the parasite. An important approach for antimalarial drug discovery is to understand critical metabolic pathways in the parasite which may help us to identify critical targets in the parasites and design specific inhibitors for these targets. Here, we have discussed proteins and pathways in different parasite organelles, i.e. apicoplast, mitochondrial and food vacuole, which have been suggested as potential drug targets; these unique parasite proteins can be targeted to develop new and novel antimalarials. In addition, we have also discussed several antimalarial projects currently under different stages of drug development pipeline. These promising antimalarial compounds have the potential to overcome multidrug resistance. Ongoing global efforts to develop new antimalarials and to identify drug targets suggest a promising future on malaria elimination and eradication