Docking of ATP analogs (ball and stick structures) into the active site of PKA (green, pdb: 1ATP) in complex with peptide substrate inhibitor (cyan). The crosslinking groups of ATP–ArN3 (A), ATP–BP (B), and ATP–DAz (C) protrude from the active site, but within close proximity to T51, G52, N171 and D184 of PKA and R18 and N20 of the peptide (red). Images with the full kinase structure are shown in Figure S15. Video images are also available as Supplementary documents.