The spread, classification, and properties of plant proteins capable of inhibiting proteinases have been reviewed. Data from the literature on the likely physiological functions of these inhibitors in plants are analyzed.

The recently described inhibitor of cysteine proteinases from Trypanosoma cruzi, chagasin, was found to have close homologs in several eukaryotes, bacteria and archaea, the first protein inhibitors of cysteine proteases in prokaryotes. These previously uncharacterized 110-130 residue-long proteins share a wellconserved sequence motif that corresponds to two adjacent ␤-strands and the short loop connecting them. Chagasin-like proteins also have other conserved, mostly aromatic, residues, and share the same predicted secondary structure. These proteins adopt an all-␤ fold with eight predicted ␤-strands of the immunoglobulin type. The phylogenetic distribution of the chagasins generally correlates with the presence of papainlike cysteine proteases. Previous studies have uncovered similar trends in cysteine proteinase binding by two unrelated inhibitors, stefin and p41, that belong to the cystatin and thyroglobulin families, respectively. A hypothetical model of chagasin-cruzipain interaction suggests that chagasin may dock to the cruzipain active site in a similar manner with the conserved NPTTG motif of chagasin forming a loop that is similar to the wedge structures formed at the active sites of papain and cathepsin L by stefin and p41.

This review analyzes the literature on various mechanisms of proteolytic enzyme inhibitors involved in plant defense against attack by phytopathogenic microorganisms. The action of proteinase inhibitors from plants upon the enzymes from pathogenic microorganisms and viruses is reviewed. Considerable attention is given to the induction of proteinase inhibitors in plants in response to the invasion of pathogens. Some aspects of application of proteinase inhibitors in biotechnology for production of transgenic plants with enhanced resistance to diseases are discussed.

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Three protein proteolytic enzyme inhibitors with molecular masses 21, 22, and 23 kDa have been isolated from intact potato tubers (Solanum tuberosum L. cv. Istrinskii). The 21 and 22 kDa proteins denoted as PSPI-21 and PSPI-22, respectively, are serine proteinase inhibitors with different specificity. The 23 kDa protein denoted as PCPI-23 is an inhibitor of plant cysteine proteinases. The PSPI-21 molecule consists of two disulfide-linked polypeptide chains with molecular masses of 16.5 kDa and 4.5 kDa. The PSPI-22 and PCPI-23 have one polypeptide chain. Their amino-termini numbered 212 5 amino acid residues have significant homology to other plant inhibitors which are members of the soybean Kunitz inhibitor family. It is found that at least PSPI-21 and PSPI-22 can predominantly accumulate in potato tubers infected with Phytophthora infestans zoospores.z 1998 Federation of European Biochemical Societies.