A novel heteromeric pantothenate kinase complex in apicomplexan parasites

Author summary Apicomplexans are a phylum of obligate intracellular parasites that cause diseases in humans and other animals, inflicting considerable burdens on human societies. During their intracellular stage, these parasites must scavenge vitamins from their host organisms in order to survive and proliferate. One such vitamin is pantothenate (vitamin B-5), which parasites convert in a universal five-step pathway to the essential metabolite coenzyme A (CoA). The first reaction in the CoA biosynthesis pathway is catalyzed by the enzyme pantothenate kinase (PanK). The genomes of humans and many other organisms, including apicomplexans, encode multiple PanK homologues, although in all studied examples, the functional PanK enzyme exists as a homodimer. In this study, we demonstrate that the two PanK homologues encoded in the genomes of the apicomplexans Plasmodium falciparum and Toxoplasma gondii, PanK1 and PanK2, exist as functional heteromeric complexes. We provide evidence that both PanK homologues contribute to the PanK activity in these parasites, and that both PanK1 and PanK2 are essential for the proliferation of T. gondii parasites specifically for their PanK activity. Our data describe the first known instances of heteromeric PanK complexes in nature and may explain why some organisms that express multiple PanKs seemingly harbor non-functional isoforms. Coenzyme A is synthesised from pantothenate via five enzyme-mediated steps. The first step is catalysed by pantothenate kinase (PanK). All PanKs characterised to date form homodimers. Many organisms express multiple PanKs. In some cases, these PanKs are not functionally redundant, and some appear to be non-functional. Here, we investigate the PanKs in two pathogenic apicomplexan parasites, Plasmodium falciparum and Toxoplasma gondii. Each of these organisms express two PanK homologues (PanK1 and PanK2). We demonstrate that PfPanK1 and PfPanK2 associate, forming a single, functional PanK complex that includes the multi-functional protein, Pf14-3-3I. Similarly, we demonstrate that TgPanK1 and TgPanK2 form a single complex that possesses PanK activity. Both TgPanK1 and TgPanK2 are essential for T. gondii proliferation, specifically due to their PanK activity. Our study constitutes the first examples of heteromeric PanK complexes in nature and provides an explanation for the presence of multiple PanKs within certain organisms.

Automated summary

This study demonstrates that PanK homologues PanK1 and PanK2 in the apicomplexans Plasmodium falciparum and Toxoplasma gondii form functional heteromeric complexes, contributing significantly to PanK activity in these parasites, particularly essential for the proliferation of T. gondii parasites. The findings describe the first instances of heteromeric PanK complexes in nature and provide insights into the presence of multiple PanK homologues in certain organisms.