The CEP19-RABL2 GTPase Complex Binds IFT-B to Initiate Intraflagellar Transport at the Ciliary Base

Publication date: Available online 15 June 2017
Source:Developmental Cell
Author(s): Tomoharu Kanie, Keene Louis Abbott, Nancie Ann Mooney, Edward Douglas Plowey, Janos Demeter, Peter Kent Jackson
Highly conserved intraflagellar transport (IFT) protein complexes direct both the assembly of primary cilia and the trafficking of signaling molecules. IFT complexes initially accumulate at the base of the cilium and periodically enter the cilium, suggesting an as-yet-unidentified mechanism that triggers ciliary entry of IFT complexes. Using affinity-purification and mass spectrometry of interactors of the centrosomal and ciliopathy protein, CEP19, we identify CEP350, FOP, and the RABL2B GTPase as proteins organizing the first known mechanism directing ciliary entry of IFT complexes. We discover that CEP19 is recruited to the ciliary base by the centriolar CEP350/FOP complex and then specifically captures GTP-bound RABL2B, which is activated via its intrinsic nucleotide exchange. Activated RABL2B then captures and releases its single effector, the intraflagellar transport B holocomplex, from the large pool of pre-docked IFT-B complexes, and thus initiates ciliary entry of IFT.

Graphical abstract

Teaser

Intraflagellar transport protein (IFT) complexes accumulate at the ciliary base and periodically enter the cilium via an unknown mechanism. Kanie et al. show that CEP19 recruits the RABL2B GTPase complex to the ciliary base, where it binds to a singular effector, IFT-B, to initiate intraflagellar transport.


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