Department of Structural Cell Biology, Max Planck Institute of Biochemistry, Martinsried, Germany.
Trypanosome Cell Biology Unit, Institut Pasteur & INSERM U1201, Paris, France.
EMBO J. 2019 May 2;38(9). doi: 10.15252/embj.2018101251. Epub 2019 Apr 2.
Intraflagellar transport (IFT) relies on motor proteins and the IFT complex to construct cilia and flagella. The IFT complex subunit IFT22/RabL5 has sequence similarity with small GTPases although the nucleotide specificity is unclear because of non-conserved G4/G5 motifs. We show that IFT22 specifically associates with G-nucleotides and present crystal structures of IFT22 in complex with GDP, GTP, and with IFT74/81. Our structural analysis unravels an unusual GTP/GDP-binding mode of IFT22 bypassing the classical G4 motif. The GTPase switch regions of IFT22 become ordered upon complex formation with IFT74/81 and mediate most of the IFT22-74/81 interactions. Structure-based mutagenesis reveals that association of IFT22 with the IFT complex is essential for flagellum construction in although IFT22 GTP-loading is not strictly required.
内鞭毛运输（IFT）依赖于马达蛋白和 IFT 复合物来构建纤毛和鞭毛。IFT 复合物亚基 IFT22/RabL5 与小 GTP 酶具有序列相似性，尽管由于非保守的 G4/G5 基序，核苷酸特异性尚不清楚。我们表明 IFT22 特异性地与 G 核苷酸结合，并展示了与 GDP、GTP 以及 IFT74/81 结合的 IFT22 的晶体结构。我们的结构分析揭示了一种不寻常的 IFT22 的 GTP/GDP 结合模式，绕过了经典的 G4 基序。IFT22 的 GTPase 开关区域在与 IFT74/81 形成复合物时变得有序，并介导 IFT22-74/81 相互作用的大部分。基于结构的诱变表明，IFT22 与 IFT 复合物的结合对于 flagellum 的构建是必不可少的，尽管 IFT22 的 GTP 加载不是严格必需的。
