Toxoplasma Tepsin is essential for transport from the trans-Golgi to the vacuole

Apicomplexans are intracellular parasites that invade and replicate within host cells. During their adaptation to this parasitic life-style these protozoans evolved numerous new organelles. Paradoxically, these parasites lost several cellular machineries which are conserved in other eukaryotes, including components involved in vesicular transport and the cytoskeleton. While some genes have been lost during evolution others might not be identifiable using bioinformatic approaches. We previously performed a phenotypic screen to determine the function of essential genes, only found in apicomplexan parasites and identified a hypothetical protein (TGGT1_301410). Here we demonstrate that this protein is a distant orthologue of Tepsin (TgTEP), an accessory protein for the adaptor complex 4 (AP4). TgTEP localises to the trans-Golgi, where it is required for the transport of material to the plant-like vacuole (PLVAC) of the parasite. Interestingly, TgTEP interacts with the AP4 and clathrin.