Inhibits trypsin; probably participates in a plant defense mechanism. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. A cyclic succinimide probably forms by loss of water between Asp-4 and Gly-5, that can then rehydrate to either the original peptide bond or to a beta-aspartyl isopeptide bond. Three isoforms of MCoTI-II are detected, two with the parent molecular weight, corresponding to the unmodified and proposed isopeptide forms, and one with a molecular weight 18 Da lower, corresponding to a succinimide cross-linked form. This is a cyclic peptide. Belongs to the protease inhibitor I7 (squash-type serine protease inhibitor) family. The genomic sequence for this protein is not available, so Asp-4 may possibly be an asparagine which is known to be more labile when immediately followed by a glycine.