The proteinase yscA-inhibitor, IA3, gene. Studies of cytoplasmic proteinase inhibitor deficiency on yeast physiology

Some properties and possible biological role of peptidase inhibitors from the entomopathogenic fungus Tolypocladium cylindrosporum

The activities of secreted and mycelial inhibitors of proteolytic enzymes from fungi of the order Hypocreales have been investigated. Inhibitors of bromelain, papain, and trypsin of low molecular mass (about 1 kDa) and a subtilisin proteinaceous inhibitor with molecular mass of 45 kDa were revealed in the culture liquid of the fungus Tolypocladium cylindrosporum. The subtilisin inhibitor from T. cylindrosporum has antibiotic properties, significantly decreased the activity of purified bacterial enzymes, and prevented the growth of the bacterium Pseudomonas sp. Data suggesting the existence in fungi of the Hypocreales order of two pools of peptidase inhibitors have been obtained.

Fungal inhibitors of proteolytic enzymes: classification, properties, possible biological roles, and perspectives for practical use

Peptidase inhibitors are ubiquitous regulatory proteins controlling catalytic activity of proteolytic enzymes. Interest in these proteins increased substantially after it became clear that they can be used for therapy of various important diseases including cancer, malaria, and autoimmune and neurodegenerative diseases. In this review we summarize available data on peptidase inhibitors from fungi, emphasizing their properties, biological role, and possible practical applications of these proteins in the future. A number of fungal peptidase inhibitors with unique structure and specificity of action have no sequence homology with other classes of peptidase inhibitors, thus representing new and specific candidates for therapeutic use. The main classifications of inhibitors in current use are considered. Available data on structure, mechanisms and conditions of action, and diversity of functions of peptidase inhibitors of fungi are analyzed. It is mentioned that on one side the unique properties of some inhibitors can be used for selective inhibition of peptidases responsible for initiation and development of pathogenic processes. On the other side, general inhibitory activity of other inhibitors towards peptidases of various catalytic classes might be able to provide efficient defense of transgenic plants against insect pests by overcoming compensatory synthesis of new peptidases by these pests in response to introduction of a fungal inhibitor. Together, the data analyzed in this review reveal that fungal inhibitors extend the spectrum of known peptidase inhibitors potentially suitable for use in medicine and agriculture.

Molecular cloning, over expression, and activity studies of a peptidic HIV-1 protease inhibitor: designed synthetic gene to functional recombinant peptide

The aspartic protease inhibitor (ATBI) purified from a Bacillus sp. is a potent inhibitor of several proteases including recombinant HIV-1 protease, pepsin, and fungal aspartic protease. In this study, we report the cloning, and over expression of a synthetic gene coding for ATBI in Escherichia coli and establish a purification protocol. The ATBI molecule consists of eleven amino acids and is peptidic in nature. We used the peptide sequence data of ATBI to synthesize complementary oligonucleotides, which were annealed and subsequently cloned in-frame with the gene for glutathione-S-transferase (GST). The expression of the resulting fusion protein was induced in E. coli BL21-A1 cells using arabinose. The recombinant peptide was purified using a reduced glutathione column, and cleaved with Factor Xa to remove the GST tag. The resultant product was further purified to homogeneity using RP-HPLC. Mass spectroscopy analysis revealed that the purified peptide had a molecular weight of 1186Da which matches the theoretical molecular weight of the amino acids present in the synthetic gene. The recombinant peptide was found to be active in vitro against HIV-1 protease, pepsin, and fungal aspartic protease. The protocol described in this study may be used to clone pharmaceutically important peptide molecules.

A novel function for the cathepsin D inhibitor in tomato

Proteinaceous aspartic proteinase inhibitors are rare in nature and are described in only a few plant species. One of them corresponds to a family of cathepsin D inhibitors (CDIs) described in potato (Solanum tuberosum), involving up to 15 isoforms with a high sequence similarity. In this work, we describe a tomato (Solanum lycopersicum) wound-inducible protein called jasmonic-induced protein 21 (JIP21). Sequence analysis of its cDNA predicted a putative function as a CDI. The JIP21 gene, whose protein has been demonstrated to be glycosylated, is constitutively expressed in flowers, stem, and fruit, and is inducible to high levels by wounding and methyl jasmonate in leaves of tomato plants. The genomic sequence of JIP21 shows that the gene is intronless and reveals the presence of both a methyl jasmonate box (TGACT) and a G-box (CACGT) in the promoter. In contrast to the presumed role of JIP21 based on sequence analysis, a detailed biochemical characterization of the purified protein uncovers a different function as a strong chymotrypsin inhibitor, which questions the previously predicted inhibitory activity against aspartic proteinases. Moreover, Egyptian cotton worm (Spodoptera littoralis) larvae fed on transgenic tomato plants overexpressing JIP21 present an increase in mortality and a delay in growth when compared with larvae fed on wild-type plants. These larvae belong to the Lepidoptera family whose main digestive enzymes have been described as being Ser proteases. All these results support the notion that tomato JIP21 should be considered as a chymotrypsin inhibitor belonging to the Ser proteinase inhibitors rather than a CDI. Therefore, we propose to name this protein tomato chymotrypsin inhibitor 21 (TCI21).

Partial purification of proteinase K inhibitors from liquid-cultured mycelia of the white rot basidiomycete Trametes versicolor

Novel protease inhibitors were isolated from liquid-cultured mycelia of the white rot fungus Trametes versicolor. Two bands of antiproteinase K activity, TvPI-A and TvPI-B, were detected in the crude cell extract by native polyacrylamide gel electrophoresis (PAGE). Proteins corresponding to TvPI-A were purified by heat treatment, anion-exchange chromatography, and gel filtration. Sodium dodecyl sulfate (SDS)-PAGE demonstrated the presence of three proteins with molecular masses of 14.5, 16.6, and 20 kDa, respectively. T. versicolor protease inhibitors suppressed the activity of proteinase K and, to a smaller extent, of Carlsberg subtilisin, whereas trypsin and chymotrypsins were not inhibited. The inhibitors were acidic proteins and showed remarkable heat stability. To our knowledge, this is the first report about proteinase K inhibitors from fungi.

Analysis of the interaction between the aspartic peptidase inhibitor SQAPI and aspartic peptidases using surface plasmon resonance

Aspartic peptidase inhibitors, which are themselves proteins, are strong inhibitors (small inhibition constants) of some aspartic peptidases but not others. However, there have been no studies of the kinetics of the interaction between a proteinaceous aspartic peptidase inhibitor and aspartic peptidases. This paper describes an analysis of rate constants for the interaction between recombinant squash aspartic peptidase inhibitor (rSQAPI) and a panel of aspartic peptidases that have a range of inhibition constants for SQAPI. Purified rSQAPI completely inhibits pepsin at a 1:1 molar ratio of pepsin to rSQAPI monomer (inhibition constant 1 nM). The interaction of pepsin with immobilized rSQAPI, at pH values between 3.0 and 6.0, was monitored using surface plasmon resonance. Binding of pepsin to rSQAPI was slow (association rate constants ca 10(4)M (-1)s(-1)), but rSQAPI was an effective pepsin inhibitor because dissociation of the rSQAPI-pepsin complex was much slower (dissociation rate constants ca 10(-4)s(-1)), especially at low pH values. Similar results were obtained with a His-tagged rSQAPI. Strong inhibition (inhibition constant 3 nM) of one isoform (rSap4) of the family of Candida albicans-secreted aspartic peptidases was, as with pepsin, characterized by slow binding of rSap4 and slower dissociation of the rSap4-inhibitor complex. In contrast, weaker inhibition of the Glomerella cingulata-secreted aspartic peptidase (inhibition constant 7 nM) and the C. albicans rSap1 and Sap2 isoenzymes (inhibition constants 25 and 400 nM, respectively) was, in each case, characterized by a larger dissociation rate constant.

The potency and specificity of the interaction between the IA3 inhibitor and its target aspartic proteinase from Saccharomyces cerevisiae

The yeast IA3 polypeptide consists of only 68 residues, and the free inhibitor has little intrinsic secondary structure. IA3 showed subnanomolar potency toward its target, proteinase A from Saccharomyces cerevisiae, and did not inhibit any of a large number of aspartic proteinases with similar sequences/structures from a wide variety of other species. Systematic truncation and mutagenesis of the IA3 polypeptide revealed that the inhibitory activity is located in the N-terminal half of the sequence. Crystal structures of different forms of IA3 complexed with proteinase A showed that residues in the N-terminal half of the IA3 sequence became ordered and formed an almost perfect alpha-helix in the active site of the enzyme. This potent, specific interaction was directed primarily by hydrophobic interactions made by three key features in the inhibitory sequence. Whereas IA3 was cut as a substrate by the nontarget aspartic proteinases, it was not cleaved by proteinase A. The random coil IA3 polypeptide escapes cleavage by being stabilized in a helical conformation upon interaction with the active site of proteinase A. This results, paradoxically, in potent selective inhibition of the target enzyme.

A high-affinity inhibitor of yeast carboxypeptidase Y is encoded by TFS1 and shows homology to a family of lipid binding proteins

A 25-kDa inhibitor of the vacuolar enzyme carboxypeptidase Y from Saccharomyces cerevisiae has been characterized. The inhibitor, Ic, binds tightly with an apparent Ki of 0.1 nM. Consistent with a cytoplasmic localization, Ic is soluble and contains no sequences which could serve as potential signals for transport into the endoplasmic reticulum. Surprisingly, Ic is encoded by TFS1, which has previously been isolated as a high-copy suppressor of cdc25-1. CDC25 encodes the putative GTP exchange factor for Ras1p/Ras2p in yeast. In an attempt to rationalize this finding, we looked for a physiological relationship by deleting or overexpressing the gene for carboxypeptidase Y in a cdc25-1 strain. However, this did not change the phenotype of this mutant strain. Ic is the first member of a new family of protease inhibitors. The inhibitor is not hydrolyzed on binding to CPY. It has fairly high degree of specificity, showing a 200-fold higher Ki toward a carboxypeptidase from Candida albicans which is highly homologous to carboxypeptidase Y. The TFS1 gene product shows extensive similarity to a class of proteins termed "21-23-kDa lipid binding proteins", members of which are found in several higher eukaryotes, including man. These proteins are highly abundant in some tissues (e.g., brain) and have in general been found to bind lipids. Considering their homology to Ic, it is tempting to speculate that they may also be inhibitors of serine carboxypeptidases.