Binding of IFT22 to the intraflagellar transport complex is essential for flagellum assembly

EMBO J. 2019 May 2;38(9):e101251. 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 Trypanosoma brucei although IFT22 GTP-loading is not strictly required.

Keywords: Trypanosoma brucei; GTPase; IFT22; cilia; intraflagellar transport.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cilia / physiology*
  • Crystallization
  • Crystallography, X-Ray
  • Flagella / physiology*
  • Guanosine Diphosphate / metabolism*
  • Guanosine Triphosphate / metabolism*
  • Protein Conformation
  • Protein Transport
  • Protozoan Proteins / chemistry*
  • Protozoan Proteins / metabolism*
  • Trypanosoma
  • Trypanosoma brucei brucei / metabolism*


  • Protozoan Proteins
  • Guanosine Diphosphate
  • Guanosine Triphosphate