title: Structural insights into the small G-protein Arl13B and implications for Joubert syndrome.
abstract: Ciliopathies are human diseases arising from defects in primary or motile cilia. The small G-protein Arl13B (ADP-ribosylation factor-like 13B) localizes to microtubule doublets of the ciliary axoneme and is mutated in Joubert syndrome. Its GDP/GTP mechanistic cycle and the effect of its mutations in patients with Joubert syndrome remain elusive. In the present study we applied high resolution structural and biochemical approaches to study Arl13B. The crystal structure of Chlamydomonas rheinhardtii Arl13B, comprising the G-domain and part of its unique C-terminus, revealed an incomplete active site, and together with biochemical data the present study accounts for the absence of intrinsic GTP hydrolysis by this protein. The structure shows that the residues representing patient mutations R79Q and R200C are involved in stabilizing important intramolecular interactions. Our studies suggest that Arg79 is crucial for the GDP/GTP conformational change by stabilizing the large two-residue register shift typical for Arf (ADP-ribosylation factor) and Arl subfamily proteins. A corresponding mutation in Arl3 induces considerable defects in effector and GAP (GTPase-activating protein) binding, suggesting a loss of Arl13B function in patients with Joubert syndrome.
authors.affiliation: *Emeritus group A. Wittinghofer, Max-Planck-Institute for Molecular Physiology, BMZ, Otto-Hahn-Straße 15, 44227 Dortmund, Germany.
authors.forename: Mandy
authors.initials: M
authors.lastname: Miertzschke
authors.affiliation: *Emeritus group A. Wittinghofer, Max-Planck-Institute for Molecular Physiology, BMZ, Otto-Hahn-Straße 15, 44227 Dortmund, Germany.
authors.forename: Carolin
authors.initials: C
authors.lastname: Koerner
authors.affiliation: †Institute of Biophysics and Physical Biochemistry, University of Regensburg, Universitätsstraße 31, 93053 Regensburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Spoerner
authors.affiliation: *Emeritus group A. Wittinghofer, Max-Planck-Institute for Molecular Physiology, BMZ, Otto-Hahn-Straße 15, 44227 Dortmund, Germany.
authors.forename: Alfred
authors.initials: A
authors.lastname: Wittinghofer
mesh_terms: D020727:ADP-Ribosylation Factors / Q000737:chemistry* / Q000235:genetics*; D000015:Abnormalities, Multiple; D000595:Amino Acid Sequence; D002526:Cerebellar Diseases / Q000235:genetics*; D002531:Cerebellum / Q000002:abnormalities; D018360:Crystallography, X-Ray; D005124:Eye Abnormalities / Q000235:genetics*; D006801:Humans; D052177:Kidney Diseases, Cystic / Q000235:genetics*; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000737:chemistry* / Q000235:genetics*; D009154:Mutation / Q000235:genetics*; D017433:Protein Structure, Secondary; D012160:Retina / Q000002:abnormalities*
chemical_list: D020727:ADP-Ribosylation Factors; C530391:ARL13B protein, human; D020559:Monomeric GTP-Binding Proteins