Endocytosis in Trypanosoma cruzi Depends on Proper Recruitment and Regulation of Functionally Redundant Myosin Motors

Abstract

Utilized by the free-living kinetoplastid Bodo saltans to feed on bacterial prey, the cytostome-cytopharynx complex (SPC) is an endocytic organelle absent from all human trypanosomatid pathogens save Trypanosoma cruzi. Building upon our previous work identifying the myosin motor MyoF as the first enzymatic component of the T. cruzi SPC, we sought to expand our understanding of this distinct organelle by identifying additional protein machinery which contribute to the endocytic process. While deletion of MyoF alone did not fully ablate endocytosis, we found that deletion of both MyoF and the similarly localized MyoC produced an endocytic-null phenotype that was rescued upon complementation. To identify potential regulatory components of this motor complex, we pulled down MyoF and identified an SPC-targeted protein that contained an annotated EF-hand calcium-binding motif that was conserved across a wide range of protozoan lineages. Surprisingly, deletion of this myosin associated protein (MyAP) alone was sufficient to produce an endocytic-null phenotype, which we were able to fully rescue via complementation. The deletion of MyAP also caused the mis-localization of both cytopharynx myosins to the cytosol. While MyAP lacking the EF-hand domain was unable to complement endocytosis, it was sufficient to restore proper myosin localization. This suggested that MyAP plays two distinct roles, one in targeting myosins to the SPC and a second in regulating myosin motor activity. Transmission electron microscopy also revealed that endocytic-null mutants lacked the electron lucent lipid inclusions typically seen in the pre-lysosomal reservosomes of T. cruzi epimastigotes. Mass spectrometry based lipidomic analysis subsequently revealed a dramatic reduction in the scavenged cholesterol content in the endocytic-null mutants, which can be attributed to an inability to endocytose exogenous lipid-protein complexes for storage in the reservosomes. Overall, this work showcases the first viable endocytic-null mutants generated in T. cruzi through specific gene deletion and highlights the feasibility of leveraging this strategy towards a full dissection of the endocytic machinery and biogenesis of the SPC. ImportanceTrypanosoma cruzi chronically infects over 7 million people in the Americas and current therapeutics are insufficient to effectively cure infection. The lack of progress in developing effective vaccines or drug treatments is due, in part, to longstanding technical limitations in studying this parasite and a lack of resources committed to support research and eradication efforts. As part of its parasitic lifestyle, T. cruzi is forced to obtain basic nutrients directly from its host environment, making the development of methods to block nutrient uptake an attractive strategy to control parasite growth and transmission. While the bulk uptake of complex nutrients by T. cruzi occurs via an endocytic structure, often referred to as the cytostome-cytopharynx complex (SPC), how exactly this tubular endocytic organelle functions at a mechanistic level has remained a mystery. In this work, we investigated the contribution of several SPC targeted myosin motors and an associated protein factor to endocytic activity. By identifying and characterizing the molecular machinery responsible for nutrient uptake, we hope to both expand our basic understanding of how this deadly pathogen acquires essential nutrients from its host, while also revealing new potential therapeutic targets to impede nutrient uptake.