Toxoplasma gondiiharbors a hypoxia-responsive coproporphyrinogen dehydrogenase-like protein

Abstract

Toxoplasma gondiiis an apicomplexan parasite that is the cause of toxoplasmosis, a potentially lethal disease for immunocompromised individuals. Duringin vivoinfection, the parasites encounter various growth environments, such as hypoxia. Therefore, the metabolic enzymes in the parasites must adapt to such changes to fulfill their nutritional requirements.Toxoplasmacande novobiosynthesize some nutrients, such as heme. The parasites heavily rely on their own heme production for intracellular survival. Notably, the antepenultimate step within this pathway is facilitated by coproporphyrinogen III oxidase (CPOX), which employs oxygen to convert coproporphyrinogen III to protoporphyrinogen IX through oxidative decarboxylation. Conversely, some bacteria can accomplish this conversion independently of oxygen through coproporphyrinogen dehydrogenase (CPDH). Genome analysis found a CPDH ortholog inToxoplasma. The mutantToxoplasmalacking CPOX displays significantly reduced growth, implying that TgCPDH potentially functions as an alternative enzyme to perform the same reaction as CPOX under low oxygen conditions. In this study, we demonstrated that TgCPDH exhibits coproporphyrinogen dehydrogenase activity by complementing it in a heme synthesis-deficientSalmonellamutant. Additionally, we observed an increase in TgCPDH expression inToxoplasmawhen it grew under hypoxic conditions. However, deletingTgCPDHin both wildtype and heme-deficient parasites did not alter their intracellular growth under both ambient and low oxygen conditions. This research marks the first report of a coproporphyrinogen dehydrogenase-like protein in eukaryotic cells. Although TgCPDH responds to hypoxic conditions and possesses enzymatic activity, our findings suggest that it does not directly affect intracellular infection or the pathogenesis ofToxoplasmaparasites.IMPORTANCEToxoplasma gondiiis a ubiquitous parasite capable of infecting a wide range of warm-blooded hosts, including humans. During its lifecycle, these parasites must adapt to varying environmental conditions, including situations with low oxygen levels. Our research, in conjunction with studies conducted by other laboratories, has revealed thatToxoplasmaprimarily relies on its own heme production during acute infections. Intriguingly, in addition to this classical heme biosynthetic pathway, the parasites encode a putative oxygen-independent coproporphyrinogen dehydrogenase, suggesting its potential contribution to heme production under varying oxygen conditions, a feature typically observed in simpler organisms like bacteria. Notably, so far, coproporphyrinogen dehydrogenase has only been identified in some bacteria for heme biosynthesis. Our study discovered thatToxoplasmaharbors a functional enzyme displaying coproporphyrinogen dehydrogenase activity, which alters its expression in the parasites when they face fluctuating oxygen levels in their surroundings.