Structures showing imidazole oriented in the active site similarly to Hpt His. (A) The co-crystal structures of CheYMPI•BeF3-•imidazole (PDB 5D2C), Spo0F•BeF3-•Spo0B (PDB 2FTK)52, SLN1•BeF3-•YPD1 (PDB 2R25)51 showing interactions between D+2, T+1, and/or T+2 side chains from each RR and the imidazole rings. CheYMPI/imidazole residues are represented by purple, Spo0F/Spo0B by cyan, SLN1/YPD1 by slate, and the phosphomimic BeF3- is green and light cyan in all three. Purple (CheY) and slate (SLN1) dots and cyan (Spo0F) spheres represent space-filling models of non-conserved active site residues. (B) Using the same coloring as panel (A) the imidazole rings from all three structures are oriented over the Be within appropriate distance for nucleophilic attack.