Light scattering determination of the stoichiometry for protease-potato serine protease inhibitor complexes

The interaction between pancreatic proteases and a serine protease inhibitor purified from potato tubers was investigated by chromatography-coupled light scattering measurements. The molar mass distribution in the chromatogram was compared to theoretical values calculated for the different possible combinations of complexes and free components by three different approaches, namely section analyses of the chromatograms, full mass average determination and mass distribution analysis. This revealed that the inhibitor was able to bind trypsin in a 2:1 complex, whereas the data for chymotrypsin clearly showed a limitation to 1:1 complex regardless of the molar ratio in the injected samples. The same experiment carried out with elastase and the potato inhibitor gave only weak indications of complex formation under the conditions used.

Zebra chip disease decreases tuber (Solanum tuberosum L.) protein content by attenuating protease inhibitor levels and increasing protease activities

Zebra chip disease of potato decreases protease inhibitor levels resulting in enhanced serine-type protease activity, decreased protein content and altered protein profiles of fully mature tubers. Zebra-chip (ZC), caused by Candidatus Liberibacter solanacearum (CLso), is a relatively new disease of potato that negatively affects growth, yield, propagation potential, and fresh and process qualities of tubers. Diseased plants produce tubers with characteristic brown discoloration of vascular tissue accompanied by elevated levels of free amino acids and reducing sugars. Here we demonstrate that ZC disease induces selective protein catabolism in tubers through modulating protease inhibitor levels. Soluble protein content of tubers from CLso-infected plants was 33% lower than from non-infected plants and electrophoretic analyses revealed substantial reductions in major tuber proteins. Patatin (~40 kDa) and ser-, asp- (22 kDa) and cys-type (85 kDa) protease inhibitors were either absent or greatly reduced in ZC-afflicted tubers. In contrast to healthy (non-infected) tubers, the proteolytic activity in CLso infected tubers was high and the ability of extracts from infected tubers to inhibit trypsin (ser-type) and papain (cys-type) proteases greatly attenuated. Moreover, extracts from CLso-infected tubers rapidly catabolized proteins purified from healthy tubers (40 kDa patatin, 22 kDa protease inhibitors, 85 kDa potato multicystatin) when subjected to proteolysis individually. In contrast, crude extracts from non-infected tubers effectively inhibited the proteolytic activity from ZC-afflicted tubers. These results suggest that the altered protein profile of ZC afflicted tubers is largely due to loss of ser- and cys-type protease inhibitors. Further analysis revealed a novel PMSF-sensitive (ser) protease (ca. 80-120 kDa) in CLso infected tubers. PMSF abolished the proteolytic activities responsible for degrading patatin, the 22 kDa protease inhibitor(s) and potato multicystatin by CLso infected tubers. The disease-induced loss of patatin and protease inhibitors therefore appears to be modulated by ser-type protease(s). The selective catabolism of proteins in ZC-afflicted tubers undoubtedly affects downstream aspects of carbohydrate and amino acid metabolism, which is ultimately reflected by the accumulation of reducing sugars, free amino acids and reduced sprouting capacity.

Structure and properties of the potato chymotrypsin inhibitor

The potato tubers contain proteins that inhibit serine proteinases and belong to subfamily of potato Kunitz-type proteinase inhibitors (PKPI). New highly purified protein had been isolated from mature potato tubers (Solanum tuberosum L., cv. Zukov's Jubilee). The protein is а single polypeptide chain of molecular, weighing 23 kDa. The 20 N-terminal amino acid residues of the protein were determined by automatic Edman procedure. On the basis of N-terminal sequence structure and the molecular mass it is indicated that the inhibitor is a potato Kunitz-type serine proteinase inhibitor that belongs to group B. It was denoted as PKCI (potato Kunitz-type chymotrypsin inhibitor). The PKCI was able to inhibit chymotrypsin and trypsin with the same degree of effectiveness. It formed equimolar complexes with both enzymes. The protein PKCI is a double-headed proteinase inhibitor and is able to bind simultaneously two molecules of different enzymes. The probable cDNA of the inhibitor, denoted as PKPIJ-B consists of a 579-bp open reading frame, encodes protein out of 193-amino acids with a signal peptide (10 residues), indicating that this protein is synthesized as a preprotein. Deduced amino acid sequence of the cDNA is aligned with the respective sequences of already known PKPI, belonging to group B.

Comparative analyses of exoproteinases produced by three phytopathogenic microorganisms

Proteinases secreted by the oomycete Phytophthora infestans (Mont.) de Bary, Rhizoctonia solani, and Fusarium culmorum belonging to different families of fungi have been studied to determine if the exoenzyme secretion depends on the environmental conditions and the phylogenetic position of the pathogen. The substrate specificity of the extracellular proteinases of F. culmorum, R. solani, and P. infestans and their sensitivity to the action of synthetic and protein inhibitors suggest that they contain trypsin-like and subtilisin-like enzymes regardless of culture medium composition. The relation of trypsin-like and subtilisin-like enzymes is dependent on the culture medium composition, especially on the form of nitrogen nutrition, particularly in the case of the exoenzymes secreted by R. solani. Phylogenetic analyses have shown that the exoproteinase set of ascomycetes and oomycetes has more similarities than basidiomycetes although they are more distant relatives. Our data suggests that the multiple proteinases secreted by pathogenic fungi could play different roles in pathogenesis, increasing the adaptability and host range, or could have different functions in survival in various ecological habitats outside the host.