Arf, Arl, Arp and Sar proteins: a family of GTP-binding proteins with a structural device for 'front-back' communication

EMBO Rep. 2002 Nov;3(11):1035-41. doi: 10.1093/embo-reports/kvf221.


Arf proteins are important regulators of cellular traffic and the founding members of an expanding family of homologous proteins and genomic sequences. They depart from other small GTP-binding proteins by a unique structural device, which we call the 'interswitch toggle', that implements front-back communication from the N-terminus to the nucleotide binding site. Here we define the sequence and structural determinants that propagate information across the protein and identify them in all of the Arf family proteins other than Arl6 and Arl4/Arl7. The positions of these determinants lead us to propose that Arf family members with the interswitch toggle device are activated by a bipartite mechanism acting on opposite sides of the protein. The presence of this communication device might provide a more useful basis for unifying Arf homologs as a family than do the cellular functions of these proteins, which are mostly unrelated. We review available genomic sequences and functional data from this perspective, and identify a novel subfamily that we call Arl8.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ADP-Ribosylation Factor 6
  • ADP-Ribosylation Factors / chemistry*
  • ADP-Ribosylation Factors / genetics
  • ADP-Ribosylation Factors / metabolism
  • Amino Acid Sequence
  • Animals
  • GTP Phosphohydrolases / chemistry*
  • GTP Phosphohydrolases / genetics
  • GTP Phosphohydrolases / metabolism
  • Guanosine Triphosphate / metabolism
  • Humans
  • Membrane Proteins / chemistry*
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Models, Molecular
  • Molecular Sequence Data
  • Monomeric GTP-Binding Proteins / chemistry*
  • Monomeric GTP-Binding Proteins / genetics
  • Monomeric GTP-Binding Proteins / metabolism
  • Protein Conformation
  • Sequence Alignment


  • ADP-Ribosylation Factor 6
  • Membrane Proteins
  • SAR protein, Lycopersicon esculentum
  • Guanosine Triphosphate
  • ADP-ribosylation factor related proteins
  • GTP Phosphohydrolases
  • ADP-Ribosylation Factors
  • Monomeric GTP-Binding Proteins