title: 3D Architecture of the Trypanosoma brucei Flagella Connector, a Mobile Transmembrane Junction.
abstract: BACKGROUND
  Cellular junctions are crucial for the formation of multicellular organisms, where they anchor cells to each other and/or supportive tissue and enable cell-to-cell communication. Some unicellular organisms, such as the parasitic protist Trypanosoma brucei, also have complex cellular junctions. The flagella connector (FC) is a three-layered transmembrane junction that moves with the growing tip of a new flagellum and attaches it to the side of the old flagellum. The FC moves via an unknown molecular mechanism, independent of new flagellum growth. Here we describe the detailed 3D architecture of the FC suggesting explanations for how it functions and its mechanism of motility.
  
  
  RESULTS
  We have used a combination of electron tomography and cryo-electron tomography to reveal the 3D architecture of the FC. Cryo-electron tomography revealed layers of repetitive filamentous electron densities between the two flagella in the interstitial zone. Though the FC does not change in length and width during the growth of the new flagellum, the interstitial zone thickness decreases as the FC matures. This investigation also shows interactions between the FC layers and the axonemes of the new and old flagellum, sufficiently strong to displace the axoneme in the old flagellum. We describe a novel filament, the flagella connector fibre, found between the FC and the axoneme in the old flagellum.
  
  
  CONCLUSIONS
  The FC is similar to other cellular junctions in that filamentous proteins bridge the extracellular space and are anchored to underlying cytoskeletal structures; however, it is built between different portions of the same cell and is unique because of its intrinsic motility. The detailed description of its structure will be an important tool to use in attributing structure / function relationships as its molecular components are discovered in the future. The FC is involved in the inheritance of cell shape, which is important for the life cycle of this human parasite.
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom.|The Boulder Laboratory for 3D Electron Microscopy of Cells, Department of MCD Biology, University of Colorado, Boulder, Colorado, United States of America.
authors.forename: Johanna L
authors.initials: JL
authors.lastname: Höög
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Lacomble
authors.affiliation: FEI Company, Hillsboro, Oregon, United States of America.
authors.forename: Cedric
authors.initials: C
authors.lastname: Bouchet-Marquis
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom.
authors.forename: Laura
authors.initials: L
authors.lastname: Briggs
authors.affiliation: The Boulder Laboratory for 3D Electron Microscopy of Cells, Department of MCD Biology, University of Colorado, Boulder, Colorado, United States of America.
authors.forename: Kristin
authors.initials: K
authors.lastname: Park
authors.affiliation: The Boulder Laboratory for 3D Electron Microscopy of Cells, Department of MCD Biology, University of Colorado, Boulder, Colorado, United States of America.
authors.forename: Andreas
authors.initials: A
authors.lastname: Hoenger
authors.affiliation: Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom.
authors.forename: Keith
authors.initials: K
authors.lastname: Gull
mesh_terms: D054468:Axoneme / Q000378:metabolism / Q000648:ultrastructure; D020285:Cryoelectron Microscopy; D005407:Flagella / Q000378:metabolism / Q000648:ultrastructure*; D006801:Humans; D015800:Protozoan Proteins / Q000378:metabolism; D014346:Trypanosoma brucei brucei / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure*; D014353:Trypanosomiasis, African / Q000469:parasitology
chemical_list: D015800:Protozoan Proteins
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