title: A G-protein activation cascade from Arl13B to Arl3 and implications for ciliary targeting of lipidated proteins.
abstract: Small G-proteins of the ADP-ribosylation-factor-like (Arl) subfamily have been shown to be crucial to ciliogenesis and cilia maintenance. Active Arl3 is involved in targeting and releasing lipidated cargo proteins from their carriers PDE6δ and UNC119a/b to the cilium. However, the guanine nucleotide exchange factor (GEF) which activates Arl3 is unknown. Here we show that the ciliary G-protein Arl13B mutated in Joubert syndrome is the GEF for Arl3, and its function is conserved in evolution. The GEF activity of Arl13B is mediated by the G-domain plus an additional C-terminal helix. The switch regions of Arl13B are involved in the interaction with Arl3. Overexpression of Arl13B in mammalian cell lines leads to an increased Arl3·GTP level, whereas Arl13B Joubert-Syndrome patient mutations impair GEF activity and thus Arl3 activation. We anticipate that through Arl13B's exclusive ciliary localization, Arl3 activation is spatially restricted and thereby an Arl3·GTP compartment generated where ciliary cargo is specifically released.
authors.affiliation: Structural Biology Group, Max Planck Institute of Molecular Physiology, Dortmund, Germany.
authors.forename: Katja
authors.initials: K
authors.lastname: Gotthardt
authors.affiliation: Structural Biology Group, Max Planck Institute of Molecular Physiology, Dortmund, Germany.
authors.forename: Mandy
authors.initials: M
authors.lastname: Lokaj
authors.affiliation: Structural Biology Group, Max Planck Institute of Molecular Physiology, Dortmund, Germany.
authors.forename: Carolin
authors.initials: C
authors.lastname: Koerner
authors.affiliation: Department of Biology, Animal Physiology, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Falk
authors.affiliation: Department of Biology, Animal Physiology, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Gießl
authors.affiliation: Structural Biology Group, Max Planck Institute of Molecular Physiology, Dortmund, Germany.
authors.forename: Alfred
authors.initials: A
authors.lastname: Wittinghofer
mesh_terms: D020727:ADP-Ribosylation Factors / Q000378:metabolism*; D000818:Animals; D002923:Cilia / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D008074:Lipoproteins / Q000378:metabolism*; D051379:Mice; D011485:Protein Binding; D025941:Protein Interaction Mapping; D021381:Protein Transport
chemical_list: C560093:Arl13b protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D008074:Lipoproteins; C490248:Arl3 protein, mouse; D020727:ADP-Ribosylation Factors
keywords: Arf-like proteins; Chlamydomonas reinhardtii; G-protein; Guanine nucleotide exchange factor; biochemistry; biophysics; cilium; human; mouse; protein trafficking; structural biology