title: The endocytic activity of the flagellar pocket in Trypanosoma brucei is regulated by an adjacent phosphatidylinositol phosphate kinase.
abstract: Phosphoinositides are spatially restricted membrane signaling molecules. Phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2]--a phosphoinositide that is highly enriched in, and present throughout, the plasma membrane--has been implicated in endocytosis. Trypanosoma brucei has one of the highest known rates of endocytosis, a process it uses to evade the immune system. To determine whether phosphoinositides play a role in endocytosis in this organism, we have identified and characterized one of the enzymes that is responsible for generating PI(4,5)P2. Surprisingly, this phosphoinositide was found to be highly concentrated in the flagellar pocket, the only site of endocytosis and exocytosis in this organism. The enzyme (designated TbPIPKA, annotated as Tb927.10.1620) was present at the neck of the pocket, towards the anterior-end of the parasite. Depletion of TbPIPKA led to depletion of PI(4,5)P2 and enlargement of the pocket, the result of impaired endocytosis. Taken together, these data suggest that TbPIPKA and its product PI(4,5)P2 are important for endocytosis and, consequently, for homeostasis of the flagellar pocket.
authors.affiliation: Max F. Perutz Laboratories, University of Vienna, Medical University of Vienna, 1030 Vienna, Austria.
authors.forename: Lars
authors.initials: L
authors.lastname: Demmel
authors.affiliation: Department of Cell Biology and Ultrastructure Research, Center for Anatomy and Cell Biology, Medical University of Vienna, 1090 Vienna, Austria.
authors.forename: Katy
authors.initials: K
authors.lastname: Schmidt
authors.affiliation: Department of Cell Biology, Howard Hughes Medical Institute, and Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, CT 06510, USA.
authors.forename: Louise
authors.initials: L
authors.lastname: Lucast
authors.affiliation: Max F. Perutz Laboratories, University of Vienna, Medical University of Vienna, 1030 Vienna, Austria.
authors.forename: Katharina
authors.initials: K
authors.lastname: Havlicek
authors.affiliation: Institute for Electron Microscopy, Graz University of Technology and Center for Electron Microscopy Graz, 8010 Graz, Austria.
authors.forename: Armin
authors.initials: A
authors.lastname: Zankel
authors.affiliation: Center for Integrative Bioinformatics, Max F. Perutz Laboratories, University of Vienna and Medical University of Vienna, 1030 Vienna, Austria.
authors.forename: Tina
authors.initials: T
authors.lastname: Koestler
authors.affiliation: University of Applied Sciences Wiener Neustadt, Department of Biomedical Analytics, 2700 Wiener Neustadt, Austria.
authors.forename: Viktoria
authors.initials: V
authors.lastname: Reithofer
authors.affiliation: Department of Cell Biology, Howard Hughes Medical Institute, and Program in Cellular Neuroscience, Neurodegeneration and Repair, Yale University School of Medicine, New Haven, CT 06510, USA.
authors.forename: Pietro
authors.initials: P
authors.lastname: de Camilli
authors.affiliation: Max F. Perutz Laboratories, University of Vienna, Medical University of Vienna, 1030 Vienna, Austria Graham.Warren@mfpl.ac.at.
authors.forename: Graham
authors.initials: G
authors.lastname: Warren
mesh_terms: D002462:Cell Membrane / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology*; D005407:Flagella / Q000378:metabolism*; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D014346:Trypanosoma brucei brucei / Q000201:enzymology / Q000378:metabolism*
chemical_list: D019269:Phosphatidylinositol 4,5-Diphosphate; D017853:Phosphotransferases (Alcohol Group Acceptor); C020077:1-phosphatidylinositol-4-phosphate 5-kinase
keywords: Endocytosis; Flagellar pocket; PI(4,5)P2; PIP kinase; Trypanosoma brucei