Arf pocket clusters. Human ADP-Ribosylation factor 1 structure ([PDB:1HUR], chain A which corresponds to Pfam Arf domain). The first five pocket clusters of this protein family are displayed by showing the centers of mass of the member pockets in 'spheres' representation (cluster 1: red, 2: green, 3: orange, 4: blue, 5: purple). The allosteric activator GDP is displayed in 'sticks' representation next to cluster 1, the Mg ion is colored yellow. Cluster 1 matches the pyrophosphate group of GDP and cluster 3 matches the pyrimidine-imidazole region of the allosteric ligand.