title: BILBO1 is a scaffold protein of the flagellar pocket collar in the pathogen Trypanosoma brucei.
abstract: The flagellar pocket (FP) of the pathogen Trypanosoma brucei is an important single copy structure that is formed by the invagination of the pellicular membrane. It is the unique site of endo- and exocytosis and is required for parasite pathogenicity. The FP consists of distinct structural sub-domains with the least explored being the annulus/horseshoe shaped flagellar pocket collar (FPC). To date the only known component of the FPC is the protein BILBO1, a cytoskeleton protein that has a N-terminus that contains an ubiquitin-like fold, two EF-hand domains, plus a large C-terminal coiled-coil domain. BILBO1 has been shown to bind calcium, but in this work we demonstrate that mutating either or both calcium-binding domains prevents calcium binding. The expression of deletion or mutated forms of BILBO1 in trypanosomes and mammalian cells demonstrate that the coiled-coil domain is necessary and sufficient for the formation of BILBO1 polymers. This is supported by Yeast two-hybrid analysis. Expression of full-length BILBO1 in mammalian cells induces the formation of linear polymers with comma and globular shaped termini, whereas mutation of the canonical calcium-binding domain resulted in the formation of helical polymers and mutation in both EF-hand domains prevented the formation of linear polymers. We also demonstrate that in T. brucei the coiled-coil domain is able to target BILBO1 to the FPC and to form polymers whilst the EF-hand domains influence polymers shape. This data indicates that BILBO1 has intrinsic polymer forming properties and that binding calcium can modulate the form of these polymers. We discuss whether these properties can influence the formation of the FPC.
authors.affiliation: University Bordeaux, Microbiologie Fondamentale et Pathogenicité, Bordeaux, France; CNRS, Microbiologie Fondamentale et Pathogénicité, UMR 5234, Bordeaux, France.
authors.forename: Célia
authors.initials: C
authors.lastname: Florimond
authors.affiliation: University Bordeaux, Microbiologie Fondamentale et Pathogenicité, Bordeaux, France; CNRS, Microbiologie Fondamentale et Pathogénicité, UMR 5234, Bordeaux, France.
authors.forename: Annelise
authors.initials: A
authors.lastname: Sahin
authors.affiliation: Max F. Perutz Laboratories, Medical University of Vienna, Vienna, Austria.
authors.forename: Keni
authors.initials: K
authors.lastname: Vidilaseris
authors.affiliation: CNRS, Microbiologie Fondamentale et Pathogénicité, UMR 5234, Bordeaux, France; Max F. Perutz Laboratories, Medical University of Vienna, Vienna, Austria.
authors.forename: Gang
authors.initials: G
authors.lastname: Dong
authors.affiliation: University Bordeaux, Microbiologie Fondamentale et Pathogenicité, Bordeaux, France; CNRS, Microbiologie Fondamentale et Pathogénicité, UMR 5234, Bordeaux, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Landrein
authors.affiliation: University Bordeaux, Microbiologie Fondamentale et Pathogenicité, Bordeaux, France; CNRS, Microbiologie Fondamentale et Pathogénicité, UMR 5234, Bordeaux, France; Institut Polytechnique de Bordeaux, Microbiologie Fondamentale et Pathogénicité, UMR-CNRS 5234, Bordeaux, France.
authors.forename: Denis
authors.initials: D
authors.lastname: Dacheux
authors.affiliation: University Bordeaux, Microbiologie Fondamentale et Pathogenicité, Bordeaux, France; CNRS, Microbiologie Fondamentale et Pathogénicité, UMR 5234, Bordeaux, France.
authors.forename: Anna
authors.initials: A
authors.lastname: Albisetti
authors.affiliation: University Bordeaux, Microbiologie Fondamentale et Pathogenicité, Bordeaux, France; CNRS, Microbiologie Fondamentale et Pathogénicité, UMR 5234, Bordeaux, France.
authors.forename: Edward H
authors.initials: EH
authors.lastname: Byard
authors.affiliation: University Bordeaux, Microbiologie Fondamentale et Pathogenicité, Bordeaux, France; CNRS, Microbiologie Fondamentale et Pathogénicité, UMR 5234, Bordeaux, France.
authors.forename: Mélanie
authors.initials: M
authors.lastname: Bonhivers
authors.affiliation: University Bordeaux, Microbiologie Fondamentale et Pathogenicité, Bordeaux, France; CNRS, Microbiologie Fondamentale et Pathogénicité, UMR 5234, Bordeaux, France.
authors.forename: Derrick R
authors.initials: DR
authors.lastname: Robinson
mesh_terms: D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D005407:Flagella / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D009154:Mutation; D055503:Protein Multimerization / Q000502:physiology*; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D014346:Trypanosoma brucei brucei / Q000235:genetics / Q000378:metabolism*
chemical_list: D002135:Calcium-Binding Proteins; D015800:Protozoan Proteins
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