Unveiling the structure of Leishmania flagella through cryoelectron tomography.

Leishmania are unicellular parasites that cause the serious disease leishmaniasis, presenting ongoing global challenges as existing treatments face issues with resistance and toxicity. Leishmania contain a single motile flagellum, essential for transmission, which has the conserved [9 + 2] microtubule arrangement. We used cryoelectron tomography to determine the ultrastructure of the Leishmania tarentolae 96-nm repeat and paraflagellar rod. While the overall structure, including three broad radial spokes and two-headed outer dynein arms, resembles other eukaryotes like Trypanosoma brucei, Tetrahymena, and Opisthokonts, the Leishmania flagellum also exhibits unique and asymmetrical features. These include asymmetrically shaped radial spoke heads similar to T. brucei, suggesting this may represent a kinetoplastid-specific feature. Further, Leishmania contain an additional inner-junction and 8-nm wide A2 protofilament hole. Strikingly, Leishmania have many doublet-specific structures such as outer dynein arm tethers, interdoublet linkers, and heterogeneous connections to the paraflagellar rod. In this work, we show that divergent structural traits of Leishmania flagella highlight lineage-specific adaptations within eukaryotes.