Loss of the BBSome perturbs endocytic trafficking and disrupts virulence of Trypanosoma brucei.
Cilia (eukaryotic flagella) are present in diverse eukaryotic lineages and have essential motility and sensory functions. The cilium's capacity to sense and transduce extracellular signals depends on dynamic trafficking of ciliary membrane proteins. This trafficking is often mediated by the Bardet-Biedl Syndrome complex (BBSome), a protein complex for which the precise subcellular distribution and mechanisms of action are unclear. In humans, BBSome defects perturb ciliary membrane protein distribution and manifest clinically as Bardet-Biedl Syndrome. Cilia are also important in several parasites that cause tremendous human suffering worldwide, yet biology of the parasite BBSome remains largely unexplored. We examined BBSome functions in Trypanosoma brucei, a flagellated protozoan parasite that causes African sleeping sickness in humans. We report that T. brucei BBS proteins assemble into a BBSome that interacts with clathrin and is localized to membranes of the flagellar pocket and adjacent cytoplasmic vesicles. Using BBS gene knockouts and a mouse infection model, we show the T. brucei BBSome is dispensable for flagellar assembly, motility, bulk endocytosis, and cell viability but required for parasite virulence. Quantitative proteomics reveal alterations in the parasite surface proteome of BBSome mutants, suggesting that virulence defects are caused by failure to maintain fidelity of the host-parasite interface. Interestingly, among proteins altered are those with ubiquitination-dependent localization, and we find that the BBSome interacts with ubiquitin. Collectively, our data indicate that the BBSome facilitates endocytic sorting of select membrane proteins at the base of the cilium, illuminating BBSome roles at a critical host-pathogen interface and offering insights into BBSome molecular mechanisms.
['Langousis|Gerasimos|G|', 'Shimogawa|Michelle M|MM|', 'Saada|Edwin A|EA|', 'Vashisht|Ajay A|AA|', 'Spreafico|Roberto|R|', 'Nager|Andrew R|AR|', 'Barshop|William D|WD|', 'Nachury|Maxence V|MV|', 'Wohlschlegel|James A|JA|', 'Hill|Kent L|KL|']
D000818:Animals D020788:Bardet-Biedl Syndrome D002966:Clathrin D004705:Endocytosis D005407:Flagella D007425:Intracellular Membranes D008565:Membrane Proteins D051379:Mice D010271:Parasites D011485:Protein Binding D021381:Protein Transport D015800:Protozoan Proteins D022161:Transport Vesicles D014346:Trypanosoma brucei brucei D014774:Virulence
BBSome virulence cilium clathrin ubiquitin