Structural basis for Arl3-specific release of myristoylated ciliary cargo from UNC119

EMBO J. 2012 Oct 17;31(20):4085-94. doi: 10.1038/emboj.2012.257. Epub 2012 Sep 7.


Access to the ciliary membrane for trans-membrane or membrane-associated proteins is a regulated process. Previously, we have shown that the closely homologous small G proteins Arl2 and Arl3 allosterically regulate prenylated cargo release from PDEδ. UNC119/HRG4 is responsible for ciliary delivery of myristoylated cargo. Here, we show that although Arl3 and Arl2 bind UNC119 with similar affinities, only Arl3 allosterically displaces cargo by accelerating its release by three orders of magnitude. Crystal structures of Arl3 and Arl2 in complex with UNC119a reveal the molecular basis of specificity. Contrary to previous structures of GTP-bound Arf subfamily proteins, the N-terminal amphipathic helix of Arl3·GppNHp is not displaced by the interswitch toggle but remains bound on the surface of the protein. Opposite to the mechanism of cargo release on PDEδ, this induces a widening of the myristoyl binding pocket. This leads us to propose that ciliary targeting of myristoylated proteins is not only dependent on nucleotide status but also on the cellular localization of Arl3.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Video-Audio Media

MeSH terms

  • ADP-Ribosylation Factors / chemistry*
  • ADP-Ribosylation Factors / metabolism
  • Adaptor Proteins, Signal Transducing / chemistry*
  • Adaptor Proteins, Signal Transducing / metabolism
  • Allosteric Regulation
  • Binding Sites
  • Caenorhabditis elegans Proteins / metabolism
  • Cilia / metabolism
  • Crystallography, X-Ray
  • Fatty Acids, Monounsaturated / metabolism
  • Fluorescence Polarization
  • GTP-Binding Protein alpha Subunits, Gi-Go / metabolism
  • GTP-Binding Proteins / chemistry
  • GTP-Binding Proteins / metabolism
  • Guanylyl Imidodiphosphate / chemistry
  • Guanylyl Imidodiphosphate / metabolism
  • Heterotrimeric GTP-Binding Proteins / metabolism
  • Humans
  • Models, Molecular
  • Peptide Fragments / chemistry
  • Peptide Fragments / metabolism
  • Protein Binding
  • Protein Conformation
  • Protein Interaction Mapping
  • Protein Processing, Post-Translational
  • Protein Structure, Tertiary
  • Structure-Activity Relationship
  • Transducin


  • Adaptor Proteins, Signal Transducing
  • Caenorhabditis elegans Proteins
  • Fatty Acids, Monounsaturated
  • GNAT1 protein, human
  • Peptide Fragments
  • UNC119 protein, human
  • odr-3 protein, C elegans
  • Guanylyl Imidodiphosphate
  • ARL2 protein, human
  • GTP-Binding Proteins
  • GTP-Binding Protein alpha Subunits, Gi-Go
  • Heterotrimeric GTP-Binding Proteins
  • Transducin
  • ADP-Ribosylation Factors
  • ARL3 protein, human
  • 9-tetradecenoic acid