Purification and characterization of a heat-stable serine protease inhibitor from the tubers of new potato variety "Golden Valley"

Antifungal activity of a trypsin inhibitor from Salvia hispanica L. (chia) seeds against fluconazole-resistant strains of Candida spp. and evaluation of its toxicity in vitro

The incidence of Candida species resistant to traditional antifungal drugs is increasing globally. This issue significantly impacts patients' lives and increases healthcare expenses, confirming the need to develop novel therapeutic strategies. Recently, a thermostable trypsin inhibitor named ShTI (11.558 kDa), which has antibacterial effects on Staphylococcus aureus, was isolated from Salvia hispanica L. (chia) seeds. This study aimed to assess the antifungal effect of ShTI against Candida species and its synergism with fluconazole and to evaluate its mode of action. Preliminary toxicological studies on mouse fibroblasts were also performed. ShTI exhibited antifungal effects against C. parapsilosis (ATCC® 22,019), C. krusei (ATCC® 6258), and six clinical fluconazole-resistant strains of C. albicans (2), C. parapsilosis (2), and C. tropicalis (2). The minimum inhibitory concentration (MIC) values were 4.1 µM (inhibiting 50% of the isolates) and 8.2 µM (inhibiting 100% of the isolates). Additionally, when combined with fluconazole, ShTI had a synergistic effect on C. albicans, altering the morphological structure of the yeast. The mode of action of ShTI against C. krusei (ATCC® 6258) and C. albicans involves cell membrane permeabilization, the overproduction of reactive oxygen species, the formation of pseudohyphae, pore formation, and consequently, cell death. In addition, ShTI (8.65 and 17.3 µM) had noncytotoxic and nongenotoxic effects on L929 mouse fibroblasts. These findings suggest that ShTI could be a promising antimicrobial candidate, but further research is necessary to advance its application as a novel antifungal agent.

Plant Protease Inhibitors as Emerging Antimicrobial Peptide Agents: A Comprehensive Review

Antimicrobial peptides (AMPs) are important mediator molecules of the innate defense mechanisms in a wide range of living organisms, including bacteria, mammals, and plants. Among them, peptide protease inhibitors (PPIs) from plants play a central role in their defense mechanisms by directly attacking pathogens or by modulating the plant's defense response. The growing prevalence of microbial resistance to currently available antibiotics has intensified the interest concerning these molecules as novel antimicrobial agents. In this scenario, PPIs isolated from a variety of plants have shown potential in inhibiting the growth of pathogenic bacteria, protozoans, and fungal strains, either by interfering with essential biochemical or physiological processes or by altering the permeability of biological membranes of invading organisms. Moreover, these molecules are active inhibitors of a range of proteases, including aspartic, serine, and cysteine types, with some showing particular efficacy as trypsin and chymotrypsin inhibitors. In this review, we provide a comprehensive analysis of the potential of plant-derived PPIs as novel antimicrobial molecules, highlighting their broad-spectrum antimicrobial efficacy, specificity, and minimal toxicity. These natural compounds exhibit diverse mechanisms of action and often multifunctionality, positioning them as promising molecular scaffolds for developing new therapeutic antibacterial agents.

The potential of plant proteins as antifungal agents for agricultural applications

Fungal pathogens induce a variety of diseases in both plants and post-harvest food crops, resulting in significant crop losses for the agricultural industry. Although the usage of chemical-based fungicides is the most common way to control these diseases, they damage the environment, have the potential to harm human and animal life, and may lead to resistant fungal strains. Accordingly, there is an urgent need for diverse and effective agricultural fungicides that are environmentally- and eco-friendly. Plants have evolved various mechanisms in their innate immune system to defend against fungal pathogens, including soluble proteins secreted from plants with antifungal activities. These proteins can inhibit fungal growth and infection through a variety of mechanisms while exhibiting diverse functionality in addition to antifungal activity. In this mini review, we summarize and discuss the potential of using plant antifungal proteins for future agricultural applications from the perspective of bioengineering and biotechnology.

Protease Inhibitors from Solanum chacoense Inhibit Pectobacterium Virulence by Reducing Bacterial Protease Activity and Motility

Potato is a major staple crop, and necrotrophic bacterial pathogens such as Pectobacterium spp. are a major threat to global food security. Most lines of cultivated potato (Solanum tuberosum) are susceptible to Pectobacterium spp., but some lines of wild potato are resistant, including Solanum chacoense M6. Despite the discovery of resistance in wild potatoes, specific resistance genes are yet to be discovered. Crude protein extract from M6 had a global effect on Pectobacterium brasiliense Pb1692 (Pb1692) virulence phenotypes. Specifically, M6 protein extracts resulted in reduced Pectobacterium exo-protease activity and motility, induced cell elongation, and affected bacterial virulence and metabolic gene expression. These effects were not observed from protein extracts of susceptible potato S. tuberosum DM1. A proteomics approach identified protease inhibitors (PIs) as candidates for S. chacoense resistance, and genomic analysis showed higher abundance and diversity of PIs in M6 than in DM1. We cloned five PIs that are unique or had high abundance in M6 compared with DM1 and purified the proteins (g18987, g28531, g39249, g40384, g6571). Four of the PIs significantly reduced bacterial protease activity, with strongest effects from g28531 and g6571. Three PIs (g18987, g28531, g6571) inhibited disease when co-inoculated with Pectobacterium pathogens into potato tubers. Two PIs (g28531, g6571) also significantly reduced Pb1692 motility and are promising as resistance genes. These results show that S. chacoense PIs contribute to bacterial disease resistance by inhibiting exo-proteases, motility, and tuber maceration and by modulating cell morphology and metabolism. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

From Naturally-Sourced Protease Inhibitors to New Treatments for Fungal Infections

Proteases are involved in a broad range of physiological processes, including host invasion by fungal pathogens, and enzymatic inhibition is a key molecular mechanism controlling proteolytic activity. Importantly, inhibitors from natural or synthetic sources have demonstrated applications in biochemistry, biotechnology, and biomedicine. However, the need to discover new reservoirs of these inhibitory molecules with improved efficacy and target range has been underscored by recent protease characterization related to infection and antimicrobial resistance. In this regard, naturally-sourced inhibitors show promise for application in diverse biological systems due to high stability at physiological conditions and low cytotoxicity. Moreover, natural sources (e.g., plants, invertebrates, and microbes) provide a large reservoir of undiscovered and/or uncharacterized bioactive molecules involved in host defense against predators and pathogens. In this Review, we highlight discoveries of protease inhibitors from environmental sources, propose new opportunities for assessment of antifungal activity, and discuss novel applications to combat biomedically-relevant fungal diseases with in vivo and clinical purpose.

Potato Industry By-Products as a Source of Protein with Beneficial Nutritional, Functional, Health-Promoting and Antimicrobial Properties

Most potato proteins are fractions of albumin and globulin, soluble in water and in water and salt solutions, respectively; these are patatin glycoproteins, with a pIs in the range of 4.8–5.2. This group of proteins is typical of potato and they are referred to as patatin or tuberin. Around 30–50% of soluble potato proteins comprise numerous fractions of protease inhibitors with a molecular weight in the range of 7–21 kDa; they are often heat-resistant, showing a wide spectrum of health-promoting effects. The nutritional value of proteins is related to the content of amino acids, their mutual proportions and digestibility. Natural proteins of the patatin fraction are characterized by favorable functional properties, including foam formation and stabilization, fat emulsification or gelling. Native potato proteins may also exhibit beneficial non-food properties, such as antimicrobial or antitumor, as well as antioxidant and antiradical. Depending on the method of isolation and the applied factors, such as pH, ionic strength and temperature, the directions of using potato protein preparations will be different.

Legumes Protease Inhibitors as Biopesticides and Their Defense Mechanisms against Biotic Factors

Legumes are affected by biotic factors such as insects, molds, bacteria, and viruses. These plants can produce many different molecules in response to the attack of phytopathogens. Protease inhibitors (PIs) are proteins produced by legumes that inhibit the protease activity of phytopathogens. PIs are known to reduce nutrient availability, which diminishes pathogen growth and can lead to the death of the pathogen. PIs are classified according to the specificity of the mechanistic activity of the proteolytic enzymes, with serine and cysteine protease inhibitors being studied the most. Previous investigations have reported the efficacy of these highly stable proteins against diverse biotic factors and the concomitant protective effects in crops, representing a possible replacement of toxic agrochemicals that harm the environment.

Purification and characterization of a novel trypsin inhibitor from Solanum tuberosum subsp. andigenum var. overa: Study of the expression levels and preliminary evaluation of its antimicrobial activity

Protease inhibitors (PIs) have been traditionally recognized by their potential biomedical application in events with exacerbation of endogenous proteases activity. Plant PIs have gained interest as naturally occurring molecules, which usually show lower environmental impact residual toxicity than synthetic compounds. In this work, we isolated, cloned, expressed and purified a novel trypsin inhibitor from S. tuberosum subsp. andigenum var. overa, named oPTI. A significant over-expression of the oPTI coding gene after 48 h exposure of methyl jasmonate compared to the gene of reference. This inhibitor showed a molecular mass of 12 kDa and a Ki of 7.3 × 10-7 M. Finally, we evaluated the antimicrobial activity of oPTI against different pathogenic microorganisms. The oPTI demonstrated inhibitory effect on the growth of Acinetobacter baumannii S-1, Acinetobacter baumannii R, Acinetobacter calcoaceticus R, Acinetobacter calcoaceticus S, Bacillus stearothermophilus, Escherichia coli, Pseudomonas aeruginosa, Salmonella braenderup, Salmonella enteritidis, Salmonella typhimurium and Yersinia enterocolitica strains. This study represents the first report for the antimicrobial activity of a plant PI over a wide range of microorganisms. Our studies reinforce the importance of natural PIs as promising molecules for their potential application in the biomedical field and/or in the food industry as natural food preservatives.

In vitro toxicological characterisation of the antifungal compound soybean toxin (SBTX)

Soybean toxin (SBTX) is a protein isolated from soybean seeds and composed of two polypeptide subunits (17 and 27 kDa). SBTX has in vitro activity against phytopathogenic fungi such as Cercospora sojina, Aspergillus niger, and Penicillium herguei, and yeasts like Candida albicans, C. parapsilosis, Kluyveromyces marxiannus, and Pichia membranifaciens. The present study aimed to analyze in vitro whether SBTX causes any side effects on non-target bacterial and mammalian cells that could impede its potential use as a novel antifungal agent. SBTX at 100 μg/mL and 200 μg/mL did not hinder the growth of the bacteria Salmonella enterica (subspecies enterica serovar choleraesuis), Bacillus subtilis (subspecies spizizenii) and Staphylococcus aureus. Moreover, SBTX at concentrations up to 500 μg/mL did not significantly affect the viability of erythrocytes, neutrophils, and human intestinal Caco-2 cells. To study whether SBTX could induce relevant alterations in gene expression, in vitro DNA microarray experiments were conducted in which differentiated Caco-2 cells were exposed for 24 h to 100 μg/mL or 200 μg/mL SBTX. SBTX up-regulated genes involved in cell cycle and immune response pathways, but down-regulated genes that play a role in cholesterol biosynthesis and platelet degranulation pathways. Thus, although SBTX did not affect bacteria, nor induced cytotoxity in mammalian cells, it affected some biological pathways in the human Caco-2 cell line that warrants further investigation.

Biotechnological, biomedical, and agronomical applications of plant protease inhibitors with high stability: A systematic review

Protease inhibitors (PIs) are regulatory proteins found in numerous animal tissues and fluids, plants, and microorganisms that reduce and inhibit the exacerbated and uncontrolled activity of the target proteases. Specific PIs are also effective tools for inactivating proteases involved in human diseases like arthritis, pancreatitis, hepatitis, cancer, AIDS, thrombosis, emphysema, hypertension, and muscular dystrophy among others. Plant PIs-small peptides with a high content of cystine residues in disulfide bridges-possess a remarkable resistance to heat treatment and a high stability against shifts in pH, denaturing agents, ionic strength, and proteolysis. In recent years, novel biologic activities have been reported for plant PIs, including antimicrobial, anticoagulant, antioxidant action plus inhibition of tumor-cell growth; thus pointing to possible applications in medicine, agriculture, and biotechnology. In this review, we provide a comparative overview of plant-PIs classifying them in four groups according of their thermal and pH stability (high stability and hyperstable -to temperature and to pHs-, respectively), then emphasizing the relevance of the physicochemical characteristics of these proteins for potential biotechnological and industrial applications. Finally, we analyze the biologic activities of the stable protease inhibitors previously characterized that are the most relevant to potential applications in biomedicine, the food industry, and agriculture.

Heterologous Expression of PKPI and Pin1 Proteinase Inhibitors Enhances Plant Fitness and Broad-Spectrum Resistance to Biotic Threats

Kunitz-type (PKPI) and Potato type I (Pin1) protease inhibitors (PIs) are two families of serine proteinase inhibitors often associated to plant storage organs and with well known insecticidal and nematicidal activities. Noteworthy, their ability to limit fungal and bacterial pathogenesis in vivo or to influence plant physiology has not been investigated in detail. To this aim, we generated a set of PVX-based viral constructs to transiently and heterologously express two potato PKPI (PKI1, PKI2) and three potato Pin1 (PPI3A2, PPI3B2, PPI2C4) genes in Nicotiana benthamiana plants, a widely used model for plant-pathogen interaction studies. Interestingly, transgenic plants expressing most of the tested PIs showed to be highly resistant against two economically important necrotrophic fungal pathogens, Botrytis cinerea and Alternaria alternata. Unexpectedly, overexpression of the PKI2 Kunitz-type or of the PPI2C4 and PPI3A2 Potato type I inhibitor genes also lead to a dramatic reduction in the propagation and symptom development produced by the bacterial pathogen Pseudomonas syringae. We further found that localized expression of PPI2C4 and PKI2 in N. benthamiana leaves caused an increase in cell expansion and proliferation which lead to tissue hypertrophy and trichome accumulation. In line with this, the systemic expression of these proteins resulted in plants with enhanced shoot and root biomass. Collectively, our results indicate that PKPI and Pin1 PIs might represent valuable tools to simultaneously increase plant fitness and broad-spectrum resistance toward phytopathogens.

Trypsin inhibitors: promising candidate satietogenic proteins as complementary treatment for obesity and metabolic disorders?

The increase in non-communicable chronic diseases has aroused interest in the research of adjuvants to the classic forms of treatments. Obesity and metabolic syndrome are the main targets of confrontation because they relate directly to other chronic diseases. In this context, trypsin inhibitors, molecules with wide heterologous application, appear as possibilities in the treatment of overweight and obesity due to the action on satiety related mechanisms, mainly in the modulation of satiety hormones, such as cholecystokinin. In addition, trypsin inhibitors have the ability to also act on some biochemical parameters related to these diseases, thus, emerging as potential candidates and promising molecules in the treatment of the obesity and metabolic syndrome. Thus, the present article proposes to approach, through a systematic literature review, the advantages, disadvantages and viabilities for the use of trypsin inhibitors directed to the treatment of overweight and obesity.

The Nutritional Value and Biological Activity of Concentrated Protein Fraction of Potato Juice

Potato protein is recognized as one of the most valuable nonanimal proteins due to the high content of essential amino acids. So far, it has not been used in human nutrition on a large scale due to technological limitations regarding its acquisition. In this study, the protein fraction of potato juice was concentrated with the use of membrane separation. The obtained potato juice protein concentrate (PJPC) was characterized in terms of nutritional value and biological activity, and the amino acid composition, mineral content, and antioxidant properties were determined. Moreover, in vitro cytotoxic activity against cancer cells of the gastrointestinal tract was investigated. The results of the present study indicate that PJPC is an excellent source of lysine and threonine, while leucine is its limiting amino acid, with an amino acid score (AAS) of 65%. Moreover, PJPC contains substantial amounts of Fe, Mn, K, and Cu. As demonstrated experimentally, PJPC is also characterized by higher antioxidant potential than potato itself. Biological activity, however, is not limited to antioxidant activity alone. Cytotoxicity studies using a gastric cancer cell line (Hs 746T), a colon cancer cell line (HT-29), and human colon normal cells (CCD 841 CoN) proved that PJPC is characterized by selective activity against cancer cells. It can thus be concluded that the developed method of producing protein concentrate from potato juice affords a product with moderate nutritional value and interesting biological activity.

Antifungal and antimicrobial proteins and peptides of potato (Solanum tuberosum L.) tubers and their applications

Potato proteins are well known for their nutritional, emulsifying, foaming, gel forming or antioxidant properties that all make from them valuable protein source for food industry. Antifungal, antimicrobial and also antiviral properties, described for potato proteins in the review, enrich the possibilities of potato protein usage. Potato proteins were divided into patatin, protease inhibitors and fraction of other proteins that also included, besides others, proteins involved in potato defence physiology. All these proteins groups provide proteins and peptides with antifungal and/or antimicrobial actions. Patatins, obtained from cultivars with resistance to Phytophthora infestans, were able to inhibit spore germination of this pathogen. Protease inhibitors represent the structurally heterogeneous group with broad range of antifungal and antimicrobial activities. Potato protease inhibitors I and II reduced the growth of Phytophthora infestans, Rhizoctonia solani and Botrytis cinerea or of the fungi of Fusarium genus. Members of Kunitz family (proteins Potide-G, AFP-J, Potamin-1 or PG-2) were able to inhibit serious pathogens such as Staphylococcus aureus, Listeria monocytogenes, Escherichia coli or Candida albicans. Potato snakins, defensins and pseudothionins are discussed for their ability to inhibit serious potato fungi as well as bacterial pathogens. Potato proteins with the ability to inhibit growth of pathogens were used for developing of pathogen-resistant transgenic plants for crop improvement. Incorporation of potato antifungal and antimicrobial proteins in feed and food products or food packages for elimination of hygienically risk pathogens brings new possibility of potato protein usage.

Anti-obesity and anti-diabetic effects of a standardized potato extract in ob/ob mice

The potato (Solanum tuberosum) has been cultivated globally for food for millenia. Potato contains proteinase inhibitor II, which catalyzes the release of cholecystokinin (CCK), leading to delayed gastric emptying in humans. The present study investigated the anti-obesity effects of Slendesta™ Potato Extract (SLD), a standardized potato extract containing 5% proteinase inhibitor II, in the ob/ob obese mice. Three doses of SLD (50, 150 or 300 mg/kg) were orally administered to ob/ob mice once a day for 28 days, whereas control mice were administered distilled water. Four weeks after SLD treatment, the changes in body weight, food consumption, epididymal fat weight, serum chemistry, insulin, leptin and adiponectin contents, and fat histopathology were determined and compared with ob/ob mice treated with 750 mg/kg conjugate linoleic acid. As a result of SLD treatment in the obese mice, body weight, food consumption, epididymal fat, serum biochemistry, histomorphological changes of fat and pancreas were significantly and dose-dependently decreased compared with ob/ob control mice. These obesity and type 2 diabetes associated alterations were significantly inhibited after SLD treatment for 28 days. Thus, the present results indicate that SLD has potential as an alternative therapeutic agent for obesity.

Fibrin(ogen)olytic and antiplatelet activities of a subtilisin-like protease from Solanum tuberosum (StSBTc-3)

Plant serine proteases have been widely used in food science and technology as well as in medicine. In this sense, several plant serine proteases have been proposed as potential anti-coagulants and anti-platelet agents. Previously, we have reported the purification and identification of a plant serine protease from Solanum tuberosum leaves. This potato enzyme, named as StSBTc-3, has a molecular weight of 72 kDa and it was characterized as a subtilisin like protease. In this work we determine and characterize the biochemical and medicinal properties of StSBTc-3. Results obtained show that, like the reported to other plant serine proteases, StSBTc-3 is able to degrade all chains of human fibrinogen and to produces fibrin clot lysis in a dose dependent manner. The enzyme efficiently hydrolyzes β subunit followed by partially hydrolyzed α and γ subunits of human fibrinogen. Assays performed to determine StSBTc-3 substrate specificity using oxidized insulin β-chain as substrate, show seven cleavage sites: Asn3-Gln4; Cys7-Gly8; Glu13-Ala14; Leu15-Tyr16; Tyr16-Leu17; Arg22-Gly23 and Phe25-Tyr26, all of them were previously reported for other serine proteases with fibrinogenolytic activity. The maximum StSBTc-3 fibrinogenolytic activity was determined at pH 8.0 and at 37 C. Additionally, we demonstrate that StSBTc-3 is able to inhibit platelet aggregation and is unable to exert cytotoxic activity on human erythrocytes in vitro at all concentrations assayed. These results suggest that StSBTc-3 could be evaluated as a new agent to be used in the treatment of thromboembolic disorders such as strokes, pulmonary embolism and deep vein thrombosis.

JcTI-I: a novel trypsin inhibitor from Jatropha curcas seed cake with potential for bacterial infection treatment

Jatropha curcas seed cake is a low-value by-product resulting from biodiesel production. The seed cake is highly toxic, but it has great potential for biotechnology applications as it is a repository of biomolecules that could be important in agriculture, medicine, and industry. To explore this potential, a novel trypsin inhibitor called JcTI-I was purified by fractionation of the crude extract with trichloroacetic acid (2.5%, v/v) followed by affinity chromatography (Trypsin-Sepharose 4B) and molecular exclusion (Sephacryl S-200). Non-reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration showed that JcTI-I has approximately 20.0~kDa. Mass spectrometry analysis revealed that the intact molecular mass of JcTI-I is 10.252~kDa. Moreover, JcTI-I is a glycoprotein with 6.4% (m/m) carbohydrates, pI of 6.6, N-terminal sequence similarity around 60% to plant albumins and high stability to heat, pH, and salinity. JcTI-I presented antibacterial activity against the human pathogenic bacteria Salmonella enterica subspecies enterica serovar choleraesuis and Staphylococcus aureus, with minimum inhibitory concentration less than 5~μg/mL. Furthermore, JcTI-I did have inhibitory activity against the serine proteases from the tested bacteria. Otherwise, no hemolytic activity of human erythrocytes and signs of acute toxicity to mice were observed for JcTI-I. The results demonstrate the benefits of J. curcas seed cake as a source of trypsin inhibitor with potential for biotechnological application as a new antimicrobial agent against human pathogenic bacteria.

PG-2, a Potent AMP against Pathogenic Microbial Strains, from Potato (Solanum tuberosum L cv. Gogu Valley) Tubers Not Cytotoxic against Human Cells

In an earlier study, we isolated potamin-1 (PT-1), a 5.6-kDa trypsin-chymotrypsin protease inhibitor, from the tubers of a potato strain (Solanum tuberosum L cv. Gogu Valley). We established that PT-1 strongly inhibits pathogenic microbial strains, but not human bacterial strains, and that its sequence shows 62% homology with a serine protease inhibitor. In the present study, we isolated an antifungal and antibacterial peptide with no cytotoxicity from tubers of the same potato strain. The peptide (peptide-G2, PG-2) was isolated using salt-extraction, ultrafiltration and reverse-phase high performance liquid chromatography (RP-HPLC). Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/MS) showed the protein to have a molecular mass of 3228.5 Da, while automated Edman degradation showed the N-terminal sequence of PG-2 to be LVKDNPLDISPKQVQALCTDLVIRCMCCC-. PG-2 exhibited antimicrobial activity against Candida albicans, a human pathogenic yeast strain, and Clavibacter michiganensis subsp. michiganensis, a plant late blight strain. PG-2 also showed antibacterial activity against Staphylococcus aureus, but did not lyse human red blood cells and was thermostable. Overall, these results suggest PG-2 may be a good candidate to serve as a natural antimicrobial agent, agricultural pesticide and/or food additive.

Potato extract (Potein) suppresses food intake in rats through inhibition of luminal trypsin activity and direct stimulation of cholecystokinin secretion from enteroendocrine cells

Dietary proteins and trypsin inhibitors are known to stimulate the secretion of the satiety hormone cholecystokinin (CCK). A potato extract (Potein) contains 60% carbohydrate and 20% protein including trypsin inhibitory proteins. In this study, we examined whether Potein suppresses food intake in rats and whether it directly stimulates CCK secretion in enteroendocrine cells. In fasted rats, food consumption was measured up to 6 h after the oral administration of Potein or soybean trypsin inhibitor (SBTI). CCK-releasing activities of Potein and SBTI were examined in the murine CCK-producing cell line STC-1. Potein inhibited the trypsin activity in vitro with a potency 20-fold lower than that of SBTI. Oral administration of Potein dose-dependently suppressed food intake for 1-6 h. Potein, but not the SBTI, dose-dependently induced CCK secretion in STC-1 cells. These results suggest that Potein suppresses food intake through the CCK secretion induced by direct stimulation on enteroendocrine cells and through inhibition of luminal trypsin.

Plant storage proteins with antimicrobial activity: novel insights into plant defense mechanisms

Storage proteins perform essential roles in plant survival, acting as molecular reserves important for plant growth and maintenance, as well as being involved in defense mechanisms by virtue of their properties as insecticidal and antimicrobial proteins. These proteins accumulate in storage vacuoles inside plant cells, and, in response to determined signals, they may be used by the different plant tissues in response to pathogen attack. To shed some light on these remarkable proteins with dual functions, storage proteins found in germinative tissues, such as seeds and kernels, and in vegetative tissues, such as tubercles and leaves, are extensively discussed here, along with the related mechanisms of protein expression. Among these proteins, we focus on 2S albumins, Kunitz proteinase inhibitors, plant lectins, glycine-rich proteins, vicilins, patatins, tarins, and ocatins. Finally, the potential use of these molecules in development of drugs to combat human and plant pathogens, contributing to the development of new biotechnology-based medications and products for agribusiness, is also presented.

A Kunitz proteinase inhibitor from corms of Xanthosoma blandum with bactericidal activity

Bacterial infections directly affect the world's population, and this situation has been aggravated by indiscriminate use of antimicrobial agents, which can generate resistant microorganisms. In this report, an initial screening of proteins with antibacterial activity from corms of 15 species of the Xanthosoma genus was conducted. Since Xanthosoma blandum corms showed enhanced activity toward bacteria, a novel protein with bactericidal activity was isolated from this particular species. Edman degradation was used for protein N-termini determination; the primary structure showed similarities with Kunitz inhibitors, and this protein was named Xb-KTI. This protein was further challenged against serine proteinases from different sources, showing clear inhibitory activities. Otherwise, no hemolytic activity was observed for Xb-KTI. The results demonstrate the biotechnological potential of Xb-KTI, the first proteinase inhibitor with antimicrobial activity described in the Xanthosoma genus.

Potato protease inhibitors inhibit food intake and increase circulating cholecystokinin levels by a trypsin-dependent mechanism

Objective

To investigate the mechanisms underlying the satiety-promoting effects of a novel protease inhibitors concentrate derived from potato (PPIC).

Methods

Acute and prolonged effects of oral PPIC administration (100 mg/kg per day) on food intake, body weight, and gastric emptying were evaluated in healthy rats. Parameters of body weight, food intake, plasma glucose, insulin, and cholecystokinin (CCK) were measured. Duodenal proteolytic activity and CCK expression were determined in tissue extracts. Intestinal STC-1 cell culture model was used to investigate the direct effect of PPIC on CCK transcript level and secretion.

Results

Acute oral administration of PPIC reduced immediate food intake during the first two hours following the treatment, delayed gastric emptying, and decreased proteolytic activity in the duodenum. Repeated oral ingestion of PPIC reduced weight gain in male rats and significantly elevated the plasma CCK levels. Although duodenal mucosal CCK mRNA levels increased in response to PPIC administration, the concentrate failed to elevate CCK expression or release in STC-1 cells. The 14-day ascending dose range study (33 to 266 mg/kg PPIC per day) showed no adverse side effects associated with PPIC administration.

Conclusion

These findings provided evidence that PPIC is effective in reducing food intake and body weight gain in healthy rats when administered orally by increasing circulating CCK levels through a trypsin-dependent mechanism.

Characterization of a highly stable trypsin-like proteinase inhibitor from the seeds of Opuntia streptacantha (O. streptacantha Lemaire)

A trypsin inhibitor from Opuntia streptacantha Lemaire (Prickly pear) seeds was purified and characterized. Of several proteases tested, this inhibitor showed specificity to trypsin-like enzymes. The major inhibitor present in these seeds showed distinctive characteristics, most notably a low molecular weight of 4.19 kDa, as determined by MALDI TOF, and an unusually high thermal stability, retaining most of the activity after heating the sample 1h to 120 degrees C with a pressure of 1 kg/cm(2). Its complete amino acid sequence was obtained through mass spectrometry, this establishing presence a blocked N-terminal region. When comparing its sequence in the MEROPS database for peptidases and peptidase inhibitors, it showed 34.48% identity with a serine-proteinase inhibitor from the I15 family.

Protease inhibitors from plants with antimicrobial activity

Antimicrobial proteins (peptides) are known to play important roles in the innate host defense mechanisms of most living organisms, including plants, insects, amphibians and mammals. They are also known to possess potent antibiotic activity against bacteria, fungi, and even certain viruses. Recently, the rapid emergence of microbial pathogens that are resistant to currently available antibiotics has triggered considerable interest in the isolation and investigation of the mode of action of antimicrobial proteins (peptides). Plants produce a variety of proteins (peptides) that are involved in the defense against pathogens and invading organisms, including ribosome-inactivating proteins, lectins, protease inhibitors and antifungal peptides (proteins). Specially, the protease inhibitors can inhibit aspartic, serine and cysteine proteinases. Increased levels of trypsin and chymotrypsin inhibitors correlated with the plants resistance to the pathogen. Usually, the purification of antimicrobial proteins (peptides) with protease inhibitor activity was accomplished by salt-extraction, ultrafiltration and C₁₈ reverse phase chromatography, successfully. We discuss the relation between antimicrobial and anti-protease activity in this review. Protease inhibitors from plants potently inhibited the growth of a variety of pathogenic bacterial and fungal strains and are therefore excellent candidates for use as the lead compounds for the development of novel antimicrobial agents.

Affinity purification of trypsin inhibitor with anti-Aspergillus flavus activity from cultivated and wild soybean

Trypsin inhibitors (TI) from wild-type soybean (Glycine soya) (WBTI) and domesticated soybean (Glycine max) (SBTI) were purified using prepared chitosan resin-trypsin as filler on the affinity chromatography column. The SBTI/WBTI purification fold by affinity chromatography was 718- and 279-fold, with the activity recovery of 62% and 59%, respectively. It was found that SBTI and WBTI exerted a strong inhibition of Aspergillus. flavus growth, with IC(50) of 1.6 and 1.0 micromol/l. This growth inhibition was possibly the result of the inhibition on alpha-amylase activity of A. flavus by both the SBTI and WBTI. This was further supported by the fact that in the presence of SBTI and WBTI at 9.0 and 6.0 microg/g (peanut) on peanuts inhibited the germination and growth of A. flavus. Accordingly, characterization of the mode of action of SBTI and WBTI could constitute a first step leading to resistance to A. flavus invasion.

Kunitz-type protease inhibitors group B fromSolanum palustre

Five Kunitz protease inhibitor group B genes were isolated from the genome of the diploid non-tuber-forming potato species Solanum palustre. Three of five new genes share 99% identity to the published KPI-B genes from various cultivated potato accessions, while others exhibit 96% identity. Spls-KPI-B2 and Spls-KPI-B4 proteins contain unique substitutions of the most conserved residues usually involved to trypsin and chymotrypsin-specific binding sites of Kunitz-type protease inhibitor (KPI)-B, respectively. To test the inhibition of trypsin and chymotrypsin by Spls-KPI proteins, five of them were produced in E. coli purified using a Ni-sepharose resin and ion-exchange chromatography. All recombinant Spls-KPI-B inhibited trypsin; K(i) values ranged from 84.8 (Spls-KPI-B4), 345.5 (Spls-KPI-B1), and 1310.6 nM (Spls-KPI-B2) to 3883.5 (Spls-KPI-B5) and 8370 nM (Spls-KPI-B3). In addition, Spls-KPI-B1 and Spls-KPI-B4 inhibited chymotrypsin. These data suggest that regardless of substitutions of key active-center residues both Spls-KPI-B4 and Spls-KPI-B1 are functional trypsin-chymotrypsin inhibitors.

Characterization of a heat-stable protein with antimicrobial activity from Arabidopsis thaliana

A heat-stable protein with antimicrobial activity was isolated from Arabidopsis thaliana plants by buffer-soluble extraction and two chromatographic procedures. The results of MALDI-TOF analysis revealed that the isolated protein shares high sequence identity with aspen SP1. To determine the exact antimicrobial properties of this protein, a cDNA encoding the protein was isolated from an A. thaliana leaf cDNA library and named AtHS1. AtHS1 mRNA was induced by exposure to external stresses, such as salicylic acid and jasmonic acid. We also analyzed the antimicrobial activity of recombinant AtHS1 expressed in Escherichia coli. This protein inhibited pathogenic fungal strains, except for Phytophthora infestans and Phytophthora nicotianae, and it exhibited antibacterial activity against E. coli and Staphylococcus aureus. These results suggest that AtHS1 shows good potential for use as a natural material in the study of antimicrobial agents.

Antifungal activity of rice Pex5p, a receptor for peroxisomal matrix proteins

We have purified a novel antifungal protein from blast fungus (Magnaporthe grisea)-treated rice leaves using consecutive chromatographies on CM-Sepharose ion-change, Affi-gel blue, and HPLC gel filtration columns. We determined the N-terminal peptide sequence of the purified protein and subjected it to the NCBI/BLAST database and found the protein to be a partial fragment of the peroxisomal receptor protein in rice (OsPex5p). After cloning two cDNAs encoding OsPEX5L and OsPEX5S genes that are splice variants of OsPEX5 from a rice leaf cDNA library, we investigated their antifungal properties. The recombinant proteins were expressed in Escherichia coli and found to significantly inhibit cell growth of various pathogenic fungal strains. mRNA expression of the OsPEX5L gene was induced by diverse external stresses such as rice blast fungus, fungal elicitor, and other signaling molecules including H(2)O(2), abscisic acid, jasmonic acid, and salicylic acid. These results suggest that the peroxisomal receptor protein, OsPex5p, plays a critical role in the rice defense system against diverse external stresses including fungal pathogenic attack.

Purification, characterization, and molecular gene cloning of an antifungal protein from Ginkgo biloba seeds

A novel basic protein with antifungal activity was isolated from the seeds of Ginkgo biloba and purified to homogeneity. The protein inhibited the growth of some fungi (Fusarium oxysporum, Trichoderma reesei, and Candida albicans) but did not exhibit antibacterial action against Escherichia coli. Furthermore, this protein showed weak inhibitory activity against the aspartic protease pepsin. To design primers for gene amplification, the NH(2)-terminal and partial internal amino acid sequences were determined using peptides obtained from a tryptic digest of the oxidized protein. The full-length cDNA of the antifungal protein was cloned and sequenced by RT-PCR and rapid amplification of cDNA ends (RACE). The cDNA contained a 402-bp open reading frame encoding a 134-aa protein with a potential signal peptide (26 residues), suggesting that this protein is synthesized as a preprotein and secreted outside the cells. The antifungal protein shows approximately 85% identity with embryo-abundant proteins from Picea abies and Picea glauca at the amino acid level; however, there is no homology between this protein and other plant antifungal proteins, such as defensin, and cyclophilin-, miraculin- and thaumatin-like proteins.

Molecular and functional characterization of a cyclophilin with antifungal activity from Chinese cabbage

An antifungal protein that inhibits the growth of filamentous fungal pathogens was isolated from Chinese cabbage (Brassica campestris L. ssp. pekinensis) by affinity chromatography on Affi-gel blue gel and ion exchange chromatography on CM-Sepharose. The N-terminal amino acid sequence of the protein was highly homologous to that of plant cyclophilins and consequently the protein was denoted as C-CyP. To understand the antifungal activity of C-CyP, we isolated a cDNA encoding its gene from a Chinese cabbage leaf cDNA library. The Chinese cabbage genome bears more than one C-CyP gene copy and C-CyP mRNA is highly expressed in all tissues except the seeds. Recombinant C-CyP catalyzed the cis-trans inter-conversion of the Ala-Pro bond of the substrate, which indicates this protein has peptidyl-prolyl cis-trans isomerase activity. It also inhibited the growth of several fungal pathogens.