A close-up look at a parasite’s propeller
High-resolution electron microscopes reveal unique structures that drive the screw-like movement of sleeping sickness parasites.
The parasites that cause African sleeping sickness, known as trypanosomes, propel themselves forward using a structure called a flagellum, a bit like the tail of a human sperm. But rather than connect to the body of the cell just at the base, like in a sperm, the parasite flagellum runs along the side of the cell. This means that, when it beats, the whole cell twists in a screw-like motion. The parasite flagellum beats vigorously, changes direction often, and puts the cell under lots of mechanical stress. This unusual motion likely helps the parasites to move through a thick and sticky fluid like blood.
The similarities between the parasite flagellum and the flagellum on a human sperm are down to a shared evolutionary history. Both structures contain the same basic molecular skeleton, known as the axoneme. The axoneme contains a combination of supporting proteins and molecular motors, and the molecular motors essentially pull on the supports to bend the flagellum.
The unusual movement of trypanosome parasites suggests that their axonemes may have unique structural features. But the three-dimensional structure of trypanosome axonemes had previously not been studied in great detail. Imhof, Zhang et al. now address this gap in knowledge using a technique called “cryo electron tomography” and showed that axoneme structure in trypanosomes does share many features with those of other organisms but it has extra proteins and connections for support, which could help to protect the flagellum from mechanical stress.
The similarities and differences between human and trypanosome flagella could indicate new drug targets that could be used to protect us against these parasites. A better understanding of how flagella work in general could also give insights into human genetic diseases that involve problems with these structures.
Originally published at https://elifesciences.org/digests/52058.
