The Trypanosoma brucei Cytoskeletal Protein KHARON Associates with Partner Proteins to Mediate Both Cytokinesis and Trafficking of Flagellar Membrane Proteins

In the African trypanosome Trypanosoma brucei, the cytoskeletal protein TbKHARON is required for trafficking of a putative Ca2+ channel to the flagellar membrane, and it is essential for parasite viability in both the mammalian stage bloodstream forms and the tsetse fly procyclic forms. This protein is located at the base of the flagellum, in the pellicular cytoskeleton, and in the mitotic spindle in both life cycle forms, and it likely serves multiple functions for these parasites. To begin to deconvolve the functions of KHARON, we have investigated partners associated with this protein and their roles in parasite biology. One KHARON associated protein, TbKHAP1, is a close interaction partner that can be crosslinked to KHARON by formaldehyde and pulled down in a molecular complex, and it colocalizes with TbKHARON at the base of the flagellum. Knockdown of TbKHAP1 mRNA has similar phenotypes to knockdown of its partner TbKHARON, impairing trafficking of the Ca2+ channel to the flagellar membrane and blocking cytokinesis, implying that the TbKHARON/TbKHAP1 complex mediates trafficking of flagellar membrane proteins. Two other KHAPs, TbKHAP2 and TbKHAP3, are in close proximity to TbKHARON but may not be direct interaction partners, and knockdown of their mRNAs does not affect trafficking of the Ca2+ channel. Two different flagellar membrane proteins, which are extruded from the flagellar membrane into extracellular vesicles, are also dependent upon TbKHARON for flagellar trafficking. These studies confirm that TbKHARON acts in complexes with other proteins to carry out various biological functions, and that some partners are involved in the core activity of targeting membrane proteins to the flagellum. Summary StatementThis study investigates the essential role in African trypanosomes of the KHARON protein and its molecular partners in trafficking of membrane proteins to the flagellum.