Variation in Basal Body Localisation and Targeting of Trypanosome RP2 and FOR20 Proteins

TOF-LisH-PLL motifs define FOP family proteins; some members are involved in flagellum assembly. The critical role of FOP family protein FOR20 is poorly understood. Here, we report relative localisations of the four FOP family proteins in parasitic Trypanosoma brucei : Tb RP2, Tb OFD1 and Tb FOP/FOP1-like are mature basal body proteins whereas Tb FOR20 is present on pro- and mature basal bodies – on the latter it localises distal to Tb RP2. We discuss how the data, together with published work for another protist Giardia intestinalis , informs on likely FOR20 function. Moreover, our localisation study provides convincing evidence that the antigen recognised by monoclonal antibody YL1/2 at trypanosome mature basal bodies is FOP family protein Tb RP2, not tyrosinated α-tubulin as widely stated in the literature. Curiously, FOR20 proteins from T. brucei and closely related African trypanosomes possess short, negatively-charged N-terminal extensions absent from FOR20 in other trypanosomatids and other eukaryotes. The extension is necessary for protein targeting, but insufficient to re-direct Tb RP2 to probasal bodies. Yet, FOR20 from the American trypanosome T. cruzi , which lacks any extension, localises to pro- and mature basal bodies when expressed in T. brucei . This identifies unexpected variation in FOR20 architecture that is presently unique to one clade of trypanosomatids.