Fig. 5. Details of the peptide binding site. (A) Schematic view of interactions, with water molecules represented as W. (B) The N-acetyl lysine slot showing the ring of water molecules around the acetyl group at the base of the slot, and the hydrophobic walls left and right. (C) The binding groove for the (K + 2) and (K + 3) peptide residues lies across the 405–408 loop between α_B and α_C. His(K + 2) packs against Phe367, and Arg(K + 3) forms hydrogen bonds back to the protein backbone. The peptide backbone forms four hydrogen bonds to the protein, three of them via water molecules.