Abstract
Parasites of the Apicomplexa phylum include species like Plasmodium falciparum and Toxoplasma gondii that are responsible for pathologies affecting humans and other animals. Most Apicomplexa contain a plastid-like organelle called the apicoplast that they inherited by secondary endosymbiosis. Because of its evolutionary history, this plastid is surrounded by four membranes across which the vast majority of apicoplast proteins, which are mostly encoded by the nucleus, must be imported in order to maintain proper organelle function. Translocation of proteins across these physical barriers is a complex journey involving sophisticated targeting mechanisms. Apicoplast proteins transit through the secretory pathway and usually carry a bipartite targeting signal composed of a signal peptide followed by a transit peptide important for specific steps of the import process. This combines classical translocons of the inner and outer chloroplast membranes with an additional endoplasmic reticulum-derived translocon machinery and its associated ubiquitin-like modifiers. Basic understanding of the molecular players that drive protein import into the apicoplast is of paramount importance, as these proteins are involved in several metabolic pathways hosted by the organelle that are vital for several apicomplexan developmental stages and are largely absent from their mammalian hosts, whic