Structure of SOTI-III in complex with pancreatic trypsin. (a) Trimeric complex of trypsin (surface representation) with SOTI-III (cartoon representation) in the asymmetric unit. (b) SOTI-III binding pocket. Cysteine residues are colored green. Disulfide bonds are labelled with residue numbers. (c) Close-up of the SOTI-III inhibitor loop (red) blocking the catalytic triad (blue). Arg32 is coordinated in the S1 pocket in a substrate-like fashion (Schechter & Berger, 1967). Dashed lines indicate hydrogen bonds. The closest hydrogen bonds of catalytic Ser200 to the inhibitor backbone are labelled in red. (d) Close-up of the subsite where Phe14 of SOTI-III is coordinated. Tyr154 of trypsin (purple) points away from residue 14.