Toxoplasma gondii apicoplast-resident ferredoxin is an essential electron transfer protein for the MEP isoprenoid biosynthetic pathway

Stephanie Henkel, Nora Frohnecke, Deborah Maus, Malcolm J. McConville, Michael Laue, Martin Blume, Frank Seeber.

Journal of Biological Chemistry. 2021 (accepted). doi: 10.1016/j.jbc.2021.101468 

Abstract:

Apicomplexan parasites, such as Toxoplasma gondii, are unusual in that each cell contains a single apicoplast, a plastid-like organelle, that compartmentalizes enzymes involved in the essential 2C-methyl-D-erythritol 4-phosphate (MEP) pathway of isoprenoid biosynthesis. The last two enzymatic steps in this organellar pathway require electrons from a redox carrier. However, the small iron-sulfur cluster-containing protein ferredoxin, a likely candidate for this function, has not been investigated in this context. We show here that inducible knockdown of T. gondii ferredoxin results in progressive inhibition of growth and eventual parasite death. Surprisingly, this phenotype is not accompanied by ultrastructural changes in the apicoplast or overall cell morphology. Knockdown of ferredoxin was instead associated with a dramatic decrease in cellular levels of the last two metabolites in isoprenoid biosynthesis, 1-hydroxy-2-methyl-2-(E)- butenyl-4-pyrophosphate and isomeric dimethylallyl pyrophosphate/isopentenyl pyrophosphate. Ferredoxin depletion was also observed to impair gliding motility, consistent with isoprenoid metabolites being important for dolichol biosynthesis, protein prenylation, and modification of other proteins involved in motility. Significantly, pharmacological inhibition of isoprenoid synthesis of the host cell exacerbated the impact of ferredoxin depletion on parasite replication, suggesting that the slow onset of parasite death following ferredoxin depletion is due to isoprenoid scavenging from the host cell and leading to partial compensation of the depleted parasite metabolites upon ferredoxin knockdown. Overall, these findings show that ferredoxin has an essential physiological function as an electron donor for the MEP pathway, and is a potential drug target for apicomplexan parasites.