Journal
BIOCHEMICAL JOURNAL
Volume 457, Issue -, Pages 301-311Publisher
PORTLAND PRESS LTD
DOI: 10.1042/BJ20131097
Keywords
Arl13B; Arl/Arf G-protein; cilia; GTPase activity; interswitch toggle; Joubert syndrome patient mutation
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Funding
- European Research Council (ERC) [268782]
- European Research Council (ERC) [268782] Funding Source: European Research Council (ERC)
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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 Are is crucial for the GDP/GTP conformational change by stabilizing the large two-residue register shift typical for Arf (ADP-ribosylation factor) and An 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.
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