Abstract
Toxoplasma gondii is a globally prevalent parasitic protist. It is well-known for its ability to infect almost all nucleated vertebrate cells, which is reflected by its unique metabolic architecture. Its fast-growing tachyzoite stage catabolizes glucose via glycolysis to yield l-lactate as a major by-product that must be exported from the cell to prevent toxicity; the underlying mechanism remains to be elucidated, however. Herein, we report three formate-nitrite transporter (FNT)-type monocarboxylate/proton symporters located in the plasma membrane of the T. gondii tachyzoite stage. We observed that all three proteins transport both l-lactate and formate in a pH-dependent manner and are inhibited by 2-hydroxy-chromanones (a class of small synthetic molecules). We also show that these compounds pharmacologically inhibit T. gondii growth. Using a chemical biology approach, we identified the critical residues in the substrate-selectivity region of the parasite transporters that determine differential specificity and sensitivity toward both substrates and inhibitors. Our findings further indicate that substrate specificity in FNT family proteins from T. gondii has evolved such that a functional repurposing of prokaryotic-type transporters helps fulfill a critical metabolic role in a clinically important parasitic protist. In summary, we have identified and characterized the lactate transporters of T. gondii and have shown that compounds blocking the FNTs in this parasite can inhibit its growth, suggesting that these transporters could have utility as potential drug targets.
Highlights
Toxoplasma gondii is a globally prevalent parasitic protist
The three TgFNT proteins display typical signature motifs, e.g. in the L2 and L5 loop regions preceding the two half-helices, and a six-transmembrane topology with both termini facing intracellularly shared by all formate–nitrite transporter (FNT) family members (Fig. 1A) [23]
These results suggest that FNT inhibitors can block the asexual reproduction of T. gondii, which resonates with our biochemical assays
Summary
Previous works by several groups have characterized lactate dehydrogenases in the two parasites [20, 21], which are meant to enable recycling of NADHϩ to NADϩ and ensure a continued glycolysis. It is still unclear how tachyzoites of T. gondii eliminate lactate produced during intracellular replication. This work focuses on the biochemical characterization, pharmacological inhibition, and mechanism of FNT proteins to demonstrate their physiological importance during the lytic cycle of T. gondii in mammalian cells
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have