Molecular modeling of human procathepsin E: analysis of salt-bridge interactions between propeptide and enzyme segment.

A three-dimensional structural model of human cathepsin E zymogen (e. g., procathepsin E) has been constructed based upon the crystal structures of porcine pepsinogen. The overall protein folding features of the model are similar to those observed in the template structures. The propeptide packs into the active-site cleft with a similar secondary structural pattern and is associated with enzyme segment by salt-bridges, hydrogen bondings, and hydrophobic interactions. As judged from the model, the salt bridges present between the propeptide and enzyme segment show remarkable variations compared to porcine pepsinogen and human progastricin structures. Mapping of these interactions revealed that human procathepsin E might engage a different structural motif (alpha-helix;12P-19P) for protecting/blocking of catalytic site compared to pepsinogen and progastricin.