LMU parasitologists have shown how Toxoplasma recycles its cell envelope – and revealed an important difference to the malaria pathogen.

According to estimates, about a third of the world’s population is infected with the single-celled parasite Toxoplasma gondii, the pathogen of toxoplasmosis. Although harmless for most people, the infection can be dangerous for unborn children and people with weakened immune systems. In these cases, the pathogen can propagate rapidly and destroy infected tissue. It obtains the energy it needs for propagation by tapping the host cell and using its resources.

Unlike with the malaria pathogen Plasmodium falciparum, which is closely related to T. gondii, scientists have lacked suitable methods to visualize this so-called endocytosis – the absorption of material from the host cell. A team led by LMU parasitologist Dr. Simon Gras has now developed a novel imaging technique that allows reliable visualization of this process for the first time. As the researchers were able to demonstrate, the material enters the pathogen through a micropore in its cell membrane. If the structure of the micropore is defective, the membrane of the parasite deforms and it dies – endocytosis is therefore important for the stability of the membrane and thus for the survival of T. gondii.

Indeed, the results obtained by the researchers showed that Toxoplasma actively recycles its membrane – that is, absorbs membrane parts through the micropore and reuses them. Moreover, membrane reservoirs are formed prior to cell division, which are then available for the formation of daughter cells. The protein Rab5b plays an important role in this recycling. When Rab5b is suppressed, the parasite cannot reuse the absorbed membrane parts and destroys them instead – which slows its growth, although does not necessarily cause its death. “Interestingly, Toxoplasma differs substantially from Plasmodium here: Whereas Toxoplasma requires Rab5b primarily for membrane organization, the protein is crucial for the survival of the malaria pathogen in terms of providing energy,” says Gras. “It follows from this that, active pharmaceutical ingredients which would target Rab5b are potentially not as effective in Toxoplasma as they could be in Plasmodium.” As such, drugs that are tailored to Plasmodium cannot automatically be used against Toxoplasma despite the close relationship between the pathogens, conclude the authors.