Fig. 1. Representation of the structural positions of the Thr27, Thr44 and Gln67 residues of Arf6 in both GDP and GTP conformations based on crystallographic studies of Arf6-GDP (PDB entry 1EOS) (Menetrey et al., 2000) and Arf6-GTPS (PDB entry 1HFV) (Pasqualato et al., 2001). Thr27 residue (in green) is involved in the binding of the magnesium ion (in copper) and the ß phosphate of the two nucleotides. Gln67 (in brown) from the switch II region and Thr44 (in purple) from the switch I region undergo a large conformational change between the two states that repositions them near the phosphate in the GTP state. Thr44 is involved in the binding of the phosphate and the magnesium ion.