A genetic screen in rodent malaria parasites identifies five new apicoplast putative membrane transporters, one of which is essential in human malaria parasites.

The malaria-causing parasite, Plasmodium, contains a unique non-photosynthetic plastid known as the apicoplast. The apicoplast is an essential organelle bound by four membranes. Although membrane transporters are attractive drug targets, only two transporters have been characterised in the malaria parasite apicoplast membranes. We selected 27 candidate apicoplast membrane proteins, 20 of which are annotated as putative membrane transporters, and performed a genetic screen in Plasmodium berghei to determine blood stage essentiality and subcellular localisation. Eight apparently essential blood stage genes were identified, three of which were apicoplast-localised: PbANKA_0614600 (DMT2), PbANKA_0401200 (ABCB4), and PbANKA_0505500. Nineteen candidates could be deleted at the blood stage, four of which were apicoplast-localised. Interestingly, three apicoplast-localised candidates lack a canonical apicoplast targeting signal but do contain conserved N-terminal tyrosines with likely roles in targeting. An inducible knockdown of an essential apicoplast putative membrane transporter, PfDMT2, was only viable when supplemented with isopentenyl diphosphate. Knockdown of PfDMT2 resulted in loss of the apicoplast, identifying PfDMT2 as a crucial apicoplast putative membrane transporter and a candidate for therapeutic intervention.

Targeting of a Transporter to the Outer Apicoplast Membrane in the Human Malaria Parasite Plasmodium falciparum.

Apicoplasts are vestigial plastids in apicomplexan parasites like Plasmodium, the causative agent of malaria. Apicomplexan parasites are dependant on their apicoplasts for synthesis of various molecules that they are unable to scavenge in sufficient quantity from their host, which makes apicoplasts attractive drug targets. Proteins known as plastid phosphate translocators (pPTs) are embedded in the outer apicoplast membrane and are responsible for the import of carbon, energy and reducing power to drive anabolic synthesis in the organelle. We investigated how a pPT is targeted into the outer apicoplast membrane of the human malaria parasite P. falciparum. We showed that a transmembrane domain is likely to act as a recessed signal anchor to direct the protein into the endomembrane system, and that a tyrosine in the cytosolic N-terminus of the protein is essential for targeting, but one or more, as yet unidentified, factors are also essential to direct the protein into the outer apicoplast membrane.