title: The intraflagellar transport protein IFT27 promotes BBSome exit from cilia through the GTPase ARL6/BBS3.
abstract: The sorting of signaling receptors into and out of cilia relies on the BBSome, a complex of Bardet-Biedl syndrome (BBS) proteins, and on the intraflagellar transport (IFT) machinery. GTP loading onto the Arf-like GTPase ARL6/BBS3 drives assembly of a membrane-apposed BBSome coat that promotes cargo entry into cilia, yet how and where ARL6 is activated remains elusive. Here, we show that the Rab-like GTPase IFT27/RABL4, a known component of IFT complex B, promotes the exit of BBSome and associated cargoes from cilia. Unbiased proteomics and biochemical reconstitution assays show that, upon disengagement from the rest of IFT-B, IFT27 directly interacts with the nucleotide-free form of ARL6. Furthermore, IFT27 prevents aggregation of nucleotide-free ARL6 in solution. Thus, we propose that IFT27 separates from IFT-B inside cilia to promote ARL6 activation, BBSome coat assembly, and subsequent ciliary exit, mirroring the process by which BBSome mediates cargo entry into cilia.
authors.affiliation: Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA; Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: Gerald M
authors.initials: GM
authors.lastname: Liew
authors.affiliation: Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: Fan
authors.initials: F
authors.lastname: Ye
authors.affiliation: Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Nager
authors.affiliation: Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: J Patrick
authors.initials: JP
authors.lastname: Murphy
authors.affiliation: Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: Jaclyn S
authors.initials: JS
authors.lastname: Lee
authors.affiliation: Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Mike
authors.initials: M
authors.lastname: Aguiar
authors.affiliation: Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: David K
authors.initials: DK
authors.lastname: Breslow
authors.affiliation: Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Steven P
authors.initials: SP
authors.lastname: Gygi
authors.affiliation: Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA. Electronic address: nachury@stanford.edu.
authors.forename: Maxence V
authors.initials: MV
authors.lastname: Nachury
mesh_terms: D020727:ADP-Ribosylation Factors / Q000378:metabolism*; D000818:Animals; D020788:Bardet-Biedl Syndrome / Q000378:metabolism; D001692:Biological Transport; D002478:Cells, Cultured; D002923:Cilia / Q000378:metabolism*; D051379:Mice; D020691:rab GTP-Binding Proteins / Q000378:metabolism*
chemical_list: C000595889:intraflagellar transport 27 protein, mouse; D020727:ADP-Ribosylation Factors; C122027:Arl6 protein, mouse; D020691:rab GTP-Binding Proteins