Genetic ablation of the mitochondrial ribosome in Plasmodium falciparum sensitizes the human malaria parasite to antimalarial drugs targeting mitochondrial functions

The mitochondrion of malaria parasites contains clinically validated drug targets. Within Plasmodium spp., the mitochondrial DNA (mtDNA) is only 6 kb long, being the smallest mitochondrial genome among all eukaryotes. The mtDNA encodes only three proteins of the mitochondrial electron transport chain and [~] 27 small, fragmented rRNA genes in length of 22-195 nucleotides. The rRNA fragments are thought to form a mitochondrial ribosome (mitoribosome), together with ribosomal proteins imported from the cytosol. The mitoribosome of Plasmodium falciparum has been shown to be essential for maintenance of the mitochondrial membrane potential and parasite viability. However, the role of mitoribosomes in sustaining the metabolic status of the parasite mitochondrion remains unknown. Here, among the 14 annotated mitoribosomal proteins of the small subunit of P. falciparum, we verified the localization and tested the essentiality of three candidates (PfmtRPS12, PfmtRPS17, PfmtRPS18), employing a CRISPR/Cas9 mediated conditional knockdown tool. Using immuno-electron microscopy, we provided evidence that the mitoribosome is closely associated with the mitochondrial inner membrane in the parasite. Upon knockdown of the mitoribosome, the parasites became hypersensitive to inhibitors targeting the bc1 complex, dihydroorotate dehydrogenase and F1Fo ATP synthase complex. Furthermore, knockdown of the mitoribosome blocked the pyrimidine biosynthesis pathway and reduced the pool of pyrimidine nucleotides. Together, our data suggest that disruption of the P. falciparum mitoribosome compromises the metabolic capability of the mitochondrion, rendering the parasite hypersensitive to a panel of inhibitors targeting mitochondrial functions.