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A mevalonate bypass system facilitates elucidation of apicoplast biology in malaria parasites

ABSTRACT: Malaria parasites rely on a plastid organelle for survival during the blood stages of infection. However, the entire organelle is dispensable as long as the isoprenoid precursor isopentenyl pyrophosphate (IPP) is supplemented in the culture medium. We engineered parasites to produce isoprenoid precursors from a mevalonate-dependent pathway, creating a parasite line that replicates normally after the loss of the apicoplast organelle. We show that carbon-labeled mevalonate is specifically incorporated into isoprenoid products, opening new avenues for researching this essential class of metabolites in malaria parasites. We also show that essential apicoplast proteins, such as the enzyme target of the drug fosmidomycin, can be deleted in this mevalonate bypass parasite line, providing a method to determine the roles of other important apicoplast-resident proteins. Several antibacterial drugs kill malaria parasites because they target basic processes, such as transcription, in the organelle. We used metabolomic and transcriptomic methods to characterize parasite metabolism after azithromycin treatment triggered loss of the apicoplast. These results provide insight into the effects of apicoplast-disrupting drugs, several of which have been used to treat malaria infections in humans. Overall, the mevalonate bypass system provides a way to probe essential aspects of apicoplast biology and study the effects of drugs that target apicoplast processes.

ORGANISM(S): Plasmodium falciparum

PROVIDER: GSE136169 | GEO | 2020/02/11

REPOSITORIES: GEO

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Project description:Plasmodium falciparum is the etiological agent of human malaria, one of the most widespread diseases in tropical and subtropical world regions. One of the biggest problems in controlling the disease is the emergence of drug resistance, which leads to the need to discover new antimalarial compounds. One of the most promissory drugs purposed is fosmidomycin, an inhibitor of the biosynthesis of isoprene units by the methylerythritol 4-phosphate (MEP) pathway which in some cases failed in clinic studies. Once formed, isoprene units are condensed to form longer structures such as farnesyl and geranylgeranyl pyrophosphate (GGPP), which are necessary for heme O and A formation, ubiquinone, and dolichyl phosphate biosynthesis as well as for protein isoprenylation. Even though the natural substrates of polyprenyl transferases and syntheses are polyprenyl pyrophosphates, it was already demonstrated that isoprenoid alcohols (polyprenols) such as farnesol (FOH) and geranylgeraniol (GGOH) can rescue parasites from fosmidomycin. This study better investigated how this rescue phenomenon occurs by performing drug-rescue assays. By this, it was observed that phytol (POH), a 20-carbon plant isoprenoid, rescues parasites from the fosmidomycin effect, similarly to FOH or GGOH. Contrarily, neither dolichols nor nonaprenol rescue parasites from fosmidomycin. Considering this, here we characterized the transport of FOH, GGOH, and POH. Once incorporated, it was observed that these substances are phosphorylated, condensed into longer isoprenoid alcohols, and incorporated into proteins and dolichyl phosphates. Through proteomic and radiolabelling approaches, it was found that prenylated proteins are naturally attached to several isoprenoids including GGOH, dolichol, and POH if exogenously added. Furthermore, results suggest the presence of at least two promiscuous protein prenyltransferases in the parasite: one enzyme which can use FPP among other unidentified substrates and another enzyme that can use GGOH, POH, and dolichols among other substrates not identified here. Thus, was obtained further evidence for dolichols and other isoprenoid products attached to proteins. This study helps better understand apicoplast-targeting antimalarials mechanism of action as well as novel posttranslational modifications of proteins.

Project description:Resistance to front-line antimalarials (artemisinin combination therapies) is spreading, and development of new drug treatment strategies to rapidly kill Plasmodium parasites that cause malaria are urgently needed. Here, we show that azithromycin—a clinically used macrolide antibiotic that targets the bacterium-like ribosome of the malaria parasites apicoplast organelle and causes a slow-killing ‘delayed death’ phenotype—can also rapidly kill parasites throughout the asexual blood-stages of the lifecycle via a ‘quick-killing’ mechanism of action. Investigation of 84 azithromycin analogues revealed nanomolar quick-killing potency that is directed against the very earliest stage of parasite development within red blood cells. Indeed, the best analogue exhibited 1600-fold higher potency than azithromycin for in vitro treatment windows less than 48 hours. Analogues were also effective against the zoonotic malaria parasite P. knowlesi, and against both multi-drug and artemisinin resistant P. falciparum lines. Metabolomic profiles of azithromycin analogue treated parasites were similar to those of chloroquine treated parasites, suggesting that the quick-killing mechanism of action may in part be localised to the parasite food vacuole. However, metabolomic signatures associated with mitochondrial disruption were also present. In addition, unlike chloroquine, azithromycin and analogues were active across blood stage development, including merozoite invasion, suggesting that these macrolides have a multi-factorial mechanism of quick-killing activity. The positioning of functional groups added to azithromycin and its quick-killing analogues altered their activity against bacterial-like ribosomes but had minimal change on quick-killing activity, which suggests that apicoplast-targeting, delayed-death activity can either be preserved or removed independently of quick-killing. Apicoplast minus parasites remained susceptible to both azithromycin and its analogues, further demonstrating that quick-killing is independent of apicoplast-targeting, delayed-death activity. Therefore, development of azithromycin and analogues as antimalarials offers the possibility of targeting parasites through both a quick-killing and delayed death mechanism of action in a single, multifactorial chemotype.

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A mevalonate bypass system facilitates elucidation of apicoplast biology in malaria parasites

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