Min Chen (Genève / CH), Szilamér Gyula Koszti (Genève / CH), Alessandro Bonavoglia (Genève / CH), Dr. Bohumil Maco (Genève / CH), Hong-Juan Peng (GuangZhou / CN), Professor Dr. Dominique Soldati-Favre (Genève / CH), Joachim Kloehn (Genève / CH)
Apicomplexan parasites, notorious for causing severe diseases like malaria (Plasmodium spp.) and toxoplasmosis (Toxoplasma gondii), harbor a distinctive organelle known as the apicoplast. The apicoplast is derived from secondary endosymbiosis and, while no longer photosynthetic, plays a pivotal role in housing metabolic functions critical for the survival of T. gondii. In this study, we aimed to dissect apicoplast functions and identify potential drug targets by bypassing the four metabolic pathways generating essential output for the parasite, namely de novo fatty acid (FA) synthesis via a prokaryotic fatty acid synthase II (FASII), synthesis of the lipid precursor lysophosphatidic acid (LPA), parts of the heme synthesis and synthesis of isopentenyl pyrophosphate (IPP) via a 2-C-methyl-D-erythritol 4-phosphate/1-deoxy-D-xylulose 5-phosphate (MEP/DOXP) pathway. To achieve this, we supplemented the culture medium with palmitate, myristate, LPA, 5-aminolevulinic acid, and mevalolactone, after genetically engineering parasites to express an MVA cassette1,2, enabling parasites to synthesize IPP from mevalonolactone independent of their endogenous pathway. Under these apicoplast-bypassing conditions, pharmacological disruption of apicoplast-resident protease FtsH1 with actinonin, led to a rapid loss of the organelle but did not kill parasites. The continuous culture of T. gondii devoid of its plastid organelle serves as a unique platform to uncover novel apicoplast functions. Comparative proteomic analysis between wildtype and apicoplast-less parasites revealed a set of downregulated proteins residing in the apicoplast. Intriguingly, some of these proteins were identified as fitness-conferring critical components involved in the biology of the organelle. In conclusion, this study sheds light on the adaptability of T. gondii to survive in the absence of the apicoplast and uncovers novel functions associated with the organelle.
1Swift R, et al. A mevalonate bypass system facilitates elucidation of plastid biology in malaria parasites PLoS Pathog. 2020 Feb 14;16(2): e1008316.
2Niu Z, et al. Two apicoplast dwelling glycolytic enzymes provide key substrates for metabolic pathways in the apicoplast and are critical for Toxoplasma growth. PLoS Pathog. 2022 Nov 30;18(11):e1011009.