Biochemical characterization of the bi-lobe reveals a continuous structural network linking the bi-lobe to other single-copied organelles in Trypanosoma brucei.

Trypanosoma brucei, a unicellular parasite, contains several single-copied organelles that duplicate and segregate in a highly coordinated fashion during the cell cycle. In the procyclic stage, a bi-lobed structure is found adjacent to the single ER exit site and Golgi apparatus, forming both stable and dynamic association with other cytoskeletal components including the basal bodies that seed the flagellum and the flagellar pocket collar that is critical for flagellar pocket biogenesis. To further understand the bi-lobe and its association with adjacent organelles, we performed proteomic analyses on the immunoisolated bi-lobe complex. Candidate proteins were localized to the flagellar pocket, the basal bodies, a tripartite attachment complex linking the basal bodies to the kinetoplast, and a segment of microtubule quartet linking the flagellar pocket collar and bi-lobe to the basal bodies. These results supported an extensive connection among the single-copied organelles in T. brucei, a strategy employed by the parasite for orderly organelle assembly and inheritance during the cell cycle.