Characterising putative transporter proteins in apicomplexan parasites identifies one that is critical for Toxoplasma gondii invasion

The apicomplexan phylum consists of a wide range of obligate intracellular parasites including the malaria-causing parasite Plasmodium falciparum and the causative agent of toxoplasmosis, Toxoplasma gondii. Transporters, a class of proteins that function in the movement of solutes and ions across biological membranes play a central role in the success of these parasites. Transporters facilitate the uptake of nutrients, removal of waste and toxins, and aid in the generation and maintenance of electrochemical ion gradients. Despite the significance of this class of proteins, relatively little is known about transporters in apicomplexan parasites. In my thesis research, I investigated uncharacterised transporter proteins that are predicted to be important for parasite proliferation and virulence. The candidate transporters that I characterised localised to a range of intracellular compartments, including the plasma membrane, trans-Golgi network and specialised parasite organelles such as the apicoplast and micronemes. Using conditional expression approaches, I demonstrated that six candidate transporters play an important role in parasite proliferation, and found that one of these had a specific role in the process by which parasites invade host cells. This is the first time a parasite solute transporter has been implicated with a function solely in the process of invasion. My work highlights the important roles transporters play in parasites and open avenues to further explore this important class of proteins.