Fig. 3.

Structural features of the active site of hCPOΔC and comparison with the active sites of pancreatic MCPs. Detailed view of the active site groove of hCPOΔC in (A) the closed conformation observed in the complex with NvCI (chain A), and in (B) the open conformation observed in the substrate-free molecule (chain B). In A and B, the side chains of those residues important for catalysis and substrate binding are shown in stick representation (in blue and magenta, respectively), and shown together with the half-transparent surface (in gray). In both panels, residues were numbered according to the amino acid position in mature hCPO. The characteristic Arg275 amino acid that determines the substrate specificity for C-t acidic residues in hCPO is located at the bottom of the active site cleft. (C) Stereoview of the active site groove of hCPOΔC in the open conformation (blue sticks), superimposed with human hCPA1 (green sticks, PDB ID code 3FJU) (42). The same residues shown in A and B were labeled and numbered according to the reference bCPA nomenclature. For the sake of better visibility of Ile255, the side chain of Ser263 (Ile243 in bCPA) has been omitted in the figure. The catalytic zinc atom is shown as a yellow sphere.