(A) An example of a structure displaying hydrophobic contacts to RS3 (PDB ID: 4lqm [54]) (B) Structures with RS3–ligand interactions. Results of the KLIFS search, which was complemented with Protein–Ligand database (PLDB) (Schrödinger LLC) that identified 197 additional structures. (C) Conformation classification of protein kinases based on DFG and αC-helix conformations as disclosed by Ung et al.[55]. The ambiguous conformations are named as ωCD, which may represent the transition conformations between the four states. Location of RS3 Cα-atom is illustrated with a blue sphere. (D) Number of structures with RS3–ligand contacts and divided by RS3 residue type and KinaMetrix [56] defined kinase conformations. For 11 structures the conformation was undefined and those were excluded.