A Sarcocystidae-Specific striated fiber assemblin protein SFA5 is required for parasite division in Toxoplasma gondii

Abstract

Apicomplexan encompass a variety of intracellular parasites responsible for significant diseases in humans and animals, such as malaria and toxoplasmosis. Among these, Toxoplasma gondii (T. gondii) serves as an exemplary organism for understanding the intricate biological characteristics of the phylum. At the parasite's apical tip, a striated fiber was discovered and proposed to be evotionarily derived from the algal flagellum. However, the protein composition (the striated fiber assemblin, SFA) of this fiber remains poorly understood. Here, we took advantage of a proximity biotin labeling approach to identify potential SFA proteins by fusion of an engeneered biotin ligase TurboID with SFA2, from which we identified several novel components of the fiber. Evolutionary analysis suggested that SFA4 is conserved in the Apicomplexa phylum with the exception of piroplasmida, while SFA5 is specific to species of Sarcocystidae. Confocal imaging analysis showed that SFA4 and SFA5 are substantially co-localized with the bait SFA2. Using a new version (OsTIR1F74G) of the plant auxin-inducible degron system that we adapted in this study, we found that SFA4 and SFA5 were efficiently depleted by addition of a much lower concentration of inducer (5-Ph-IAA, instead of IAA). Detailed phenotypical analyses demonstrated that SFA5 is essential for daughter parasite formation and separation of parasite nuclei during division, supporting the localization of SFA5 at the striated fiber that connects the centriole and the apical conoid. The mouse assay suggested the essentiality of SFA5 in the parasites. Thus, this study provided a new repertoile of the stiated fiber, and new data supporting association of the fiber with parasite division.