Fig. 3. Structural context of the P1 side chain in the S1 binding pocket. β-Trypsin is shown in cartoon representation and the modified BPTI in stick representation (a) Lys15 and structural water molecules A′, D′, and E′, and (b) Lys15TfeGly and structural water molecules A, B, C, D, and E, and (c) superimposition of P1 side chains and structural water molecules.