Kanie Tomoharu, Abbott Keene Louis, Mooney Nancie Ann, Plowey Edward Douglas, Demeter Janos, Jackson Peter Kent
Baxter Laboratory, Department of Microbiology & Immunology, Stanford University School of Medicine, Stanford, CA 94305, USA.
Department of Pathology, Stanford University School of Medicine, Stanford, CA 94305, USA.
Dev Cell. 2017 Jul 10;42(1):22-36.e12. doi: 10.1016/j.devcel.2017.05.016. Epub 2017 Jun 15.
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.
高度保守的鞭毛内运输（IFT）蛋白复合物既指导初级纤毛的组装，又参与信号分子的运输。IFT复合物最初在纤毛基部积累，并周期性地进入纤毛，这表明存在一种尚未确定的机制来触发IFT复合物进入纤毛。通过对中心体和纤毛病相关蛋白CEP19的相互作用蛋白进行亲和纯化和质谱分析，我们确定CEP350、FOP和RABL2B GTP酶是组织首个已知的指导IFT复合物进入纤毛机制的蛋白。我们发现CEP19被中心粒CEP350/FOP复合物招募到纤毛基部，然后特异性捕获结合GTP的RABL2B，RABL2B通过其内在的核苷酸交换被激活。激活的RABL2B随后从大量预先停靠的IFT-B复合物池中捕获并释放其单一效应器——鞭毛内运输B全复合物，从而启动IFT进入纤毛。
