Discussion

The flagellar pocket is the site of all endo- and exocytic traffic in trypanosomes. Clustered around the neck of the flagellar pocket on its cytoplasmic face are a number of cytoskeletal complexes whose functions remain relatively unexplored. The best characterised of these is the flagellar pocket collar, which has been shown to be essential for flagellar pocket biogenesis. Situated atop the flagellar pocket collar is the hook complex, a multiprotein fishhook-shaped structure containing the repeat motif protein TbMORN1. The morphology and composition of the hook complex have been previously interrogated using imaging and proximity-dependent biotinylation, respectively. Depletion of TbMORN1 in bloodstream form Trypanosoma brucei results in the generation of a BigEye (enlarged flagellar pocket) phenotype and subsequent cell lysis. Functional analysis of these TbMORN1-depleted cells suggests that the hook complex may be acting as a kind of molecular valve to regulate the entry of macromolecules into the flagellar pocket (the “flux capacitor” hypothesis).