Ciliary targeting motif VxPx directs assembly of a trafficking module through Arf4

EMBO J. 2009 Feb 4;28(3):183-92. doi: 10.1038/emboj.2008.267. Epub 2009 Jan 15.


Dysfunctions of primary cilia and cilia-derived sensory organelles underlie a multitude of human disorders, including retinal degeneration, yet membrane targeting to the cilium remains poorly understood. Here, we show that the newly identified ciliary targeting VxPx motif present in rhodopsin binds the small GTPase Arf4 and regulates its association with the trans-Golgi network (TGN), which is the site of assembly and function of a ciliary targeting complex. This complex is comprised of two small GTPases, Arf4 and Rab11, the Rab11/Arf effector FIP3, and the Arf GTPase-activating protein ASAP1. ASAP1 mediates GTP hydrolysis on Arf4 and functions as an Arf4 effector that regulates budding of post-TGN carriers, along with FIP3 and Rab11. The Arf4 mutant I46D, impaired in ASAP1-mediated GTP hydrolysis, causes aberrant rhodopsin trafficking and cytoskeletal and morphological defects resulting in retinal degeneration in transgenic animals. As the VxPx motif is present in other ciliary membrane proteins, the Arf4-based targeting complex is most likely a part of conserved machinery involved in the selection and packaging of the cargo destined for delivery to the cilium.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, N.I.H., Intramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • ADP-Ribosylation Factors / metabolism*
  • Actin Cytoskeleton / metabolism
  • Adaptor Proteins, Signal Transducing / metabolism
  • Amino Acid Motifs
  • Amino Acid Sequence
  • Animals
  • Animals, Genetically Modified
  • Cilia / metabolism*
  • Cilia / ultrastructure
  • GTPase-Activating Proteins / metabolism
  • Guanosine Triphosphate / metabolism
  • Hydrolysis
  • I-kappa B Kinase / chemistry
  • I-kappa B Kinase / metabolism
  • Intracellular Membranes / metabolism
  • Intracellular Membranes / ultrastructure
  • Molecular Sequence Data
  • Mutant Proteins / metabolism
  • Organ Specificity
  • Protein Binding
  • Protein Sorting Signals
  • Protein Structure, Tertiary
  • Protein Transport
  • Retinal Degeneration / metabolism
  • Rhodopsin / chemistry*
  • Rhodopsin / metabolism*
  • Xenopus / genetics
  • Xenopus Proteins / metabolism*
  • rab GTP-Binding Proteins / metabolism
  • trans-Golgi Network / ultrastructure


  • Adaptor Proteins, Signal Transducing
  • GTPase-Activating Proteins
  • Mutant Proteins
  • Protein Sorting Signals
  • Xenopus Proteins
  • Guanosine Triphosphate
  • Rhodopsin
  • I-kappa B Kinase
  • rab11 protein
  • ADP-Ribosylation Factors
  • Arf4 protein, Xenopus
  • rab GTP-Binding Proteins