Biochemical analysis of PIFTC3, the Trypanosoma brucei orthologue of nematode DYF-13, reveals interactions with established and putative intraflagellar transport components

DYF-13, originally identified in Caenorhabditis elegans within a collection of dye-filling chemosensory mutants, is one of several proteins that have been classified as putatively involved in intraflagellar transport (IFT), the bidirectional movement of protein complexes along cilia and flagella and specifically in anterograde IFT. Although genetic studies have highlighted a fundamental role of DYF-13 in nematode sensory cilium and trypanosome flagellum biogenesis, biochemical studies on DYF-13 have lagged behind. Here, we show that in Trypanosoma brucei the orthologue to DYF-13, PIFTC3, participates in a macromolecular complex of approximately 660 kDa. Mass spectroscopy of affinity-purified PIFTC3 revealed several components of IFT complex B as well as orthologues of putative IFT factors DYF-1, DYF-3, DYF-11/Elipsa and IFTA-2. DYF-11 was further analysed and shown to be concentrated near the basal bodies and in the flagellum, and to be required for flagellum elongation. In addition, by coimmunoprecipitation we detected an interaction between DYF-13 and IFT122, a component of IFT complex A, which is required for retrograde transport. Thus, our biochemical analysis supports the model, proposed by genetic analysis in C. elegans, that the trypanosome orthologue of DYF-13 plays a central role in the IFT mechanism.