InterPro domain: IPR036354

This family of proteinase inhibitors belong to MEROPS inhibitor family I13, clan IG. They inhibit peptidases of the S1 ( IPR001254 ) and S8 ( IPR000209 ) families [ 1 ]. Potato inhibitor type I sequences are not solely restricted to potatoes but are found in other plant species for example: barley endosperm chymotrypsin inhibitor [ 2 ], and pumpkin trypsin inhibitor. Apart from leeches, e.g.Hirudo medicinalis (Medicinal leech), homologues are not found in metazoa [ 3 ]. In general, the proteins have retained a specificity towards chymotrypsin-like and elastase-like proteases. Structurally these inhibitors are small (60 to 90 residues) and in contrast with other families of protease inhibitors, they lack disulphide bonds. The inhibitor is a wedge-shaped molecule, its pointed edge formed by the protease-binding loop, which contains the scissile bond. The loop binds tightly to the protease active site, subsequent cleavage of the scissile bond causing inhibition of the enzyme [ 4 ].

The inhibitors (designated type I and II) are synthesised in potato tubers, increasing in concentration as the tuber develops. Synthesis of the inhibitors throughout the plant is also induced by leaf damage; this systemic response being triggered by the release of a putative plant hormone.

Examples found in the bacteria and archaea are probable false positives.

1. Evolutionary families of peptidase inhibitors. Biochem. J. 378, 705-16
2. Nucleotide sequence of barley chymotrypsin inhibitor-2 (CI-2) and its expression in normal and high-lysine barley. Eur. J. Biochem. 165, 99-106
3. Refined 1.2 A crystal structure of the complex formed between subtilisin Carlsberg and the inhibitor eglin c. Molecular structure of eglin and its detailed interaction with subtilisin. EMBO J. 5, 813-8