A single Na+-Pi cotransporter in Toxoplasma plays key roles in phosphate import and control of parasite osmoregulation

Abstract

Inorganic ions such as phosphate, are essential nutrients required for a broad spectrum of cellular functions and regulation. During infection, pathogens must obtain inorganic phosphate (Pi) from the host. Despite the essentiality of phosphate for all forms of life, how the intracellular parasite Toxoplasma gondii acquires Pi from the host cell is still unknown. In this study, we demonstrated that Toxoplasma actively internalizes exogenous Pi by exploiting a gradient of Na+ ions to drive Pi uptake across the plasma membrane. The Na+-dependent phosphate transport mechanism is electrogenic and functionally coupled to a cipargarmin sensitive Na+-H+-ATPase. Toxoplasma expresses one transmembrane Pi transporter harboring PHO4 binding domains that typify the PiT Family. This transporter named TgPiT, localizes to the plasma membrane, the inward buds of the endosomal organelles termed VAC, and many cytoplasmic vesicles. Upon Pi limitation in the medium, TgPiT is more abundant at the plasma membrane. We genetically ablated the PiT gene, and ΔTgPiT parasites are impaired in importing Pi and synthesizing polyphosphates. Interestingly, ΔTgPiT parasites accumulate 4-times more acidocalcisomes, storage organelles for phosphate molecules, as compared to parental parasites. In addition, these mutants have a reduced cell volume, enlarged VAC organelles, defects in calcium storage and a slightly alkaline pH. Overall, these mutants exhibit severe growth defects and have reduced acute virulence in mice. In survival mode, ΔTgPiT parasites upregulate several genes, including those encoding enzymes that cleave or transfer phosphate groups from phosphometabolites, transporters and ions exchangers localized to VAC or acidocalcisomes. Taken together, these findings point to a critical role of TgPiT for Pi supply for Toxoplasma and also for protection against osmotic stresses.

Metabolic flexibilities and vulnerabilities in the pentose phosphate pathway of the zoonotic pathogen Toxoplasma gondii

“…On the other hand, disruption of Tg G6PDHs will block NADPH synthesis but maintain the intact downstream pathway. A previous study has reported that Toxoplasma expresses a phosphate transporter that plays a crucial role in the phosphate import [ 35 ]. There may be transporters in the parasite membrane to import 6-phosphogluconate and possibly other host-derived PPP intermediates that can sustain (low-level) synthesis of NADPH in the Δg6pdh1Δg6pdh2 strain.…”

A Coccidia-Specific Phosphate Transporter Is Essential for the Growth of Toxoplasma gondii Parasites

“…1 ). This protein was named TgPiT, and it has Na + -dependent inorganic phosphate transport activity, as reported recently ( 35 ). TgPiT is widely present and conserved in apicomplexan parasites, including Plasmodium ( Fig.…”

“…The Toxoplasma ortholog (TgPiT) of PfPiT shows similar phosphate-transporting activity. TgPiT deletion results in reduced inorganic phosphate import and polyphosphate synthesis ( 35 ). Unexpectedly, the Δ Tgpit mutants only showed a modest growth defect and virulence attenuation ( 35 ).…”

“…TgPiT deletion results in reduced inorganic phosphate import and polyphosphate synthesis ( 35 ). Unexpectedly, the Δ Tgpit mutants only showed a modest growth defect and virulence attenuation ( 35 ). Given the essential role of phosphorous to all cells, these findings suggest that there must be other phosphate acquisition pathways in Toxoplasma .…”

Lessons from protozoans: Phosphate sensing and polyphosphate storage in fungi

“…The later identification of VTC as the key mediator of PolyP synthesis in fungi vacuoles and protozoan acidocalcisomes comprises one more similarity between these 2 models. Further studies using vtc mutants confirmed that PolyP storage in acidocalcisomes is important for the virulence and/or survival under infection conditions of trypanosomatid and apicomplexan protozoans [ 30 – 33 ]. More recently, a conserved role for InsP in regulating Pi homeostasis by interaction with SPX domains has also emerged in Trypanosoma brucei [ 34 ].…”