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

Protein extract of Bromelia karatas L. rich in cysteine proteases (ananain- and bromelain-like) has antibacterial activity against foodborne pathogens Listeria monocytogenes and Salmonella Typhimurium

Bromelia karatas L. is a plant species from the Americas. The presence of proteases in fruits of B. karatas has been reported but scarcely studied in detail. Proteolytic enzymes from Ananas comosus have displayed antifungal and antibacterial activity. Thus, novel proteases present in B. karatas may be useful as a source of compounds against microorganisms in medicine and food production. In this work, the protein extract from the fruits of B. karatas was characterized and its antibacterial activity against Salmonella Typhimurium and Listeria monocytogenes was determined for the first time. Proteins highly similar to ananain and the fruit bromelain from A. comosus were identified as the main proteases in B. karatas fruits using liquid chromatography with tandem mass spectrometry (LC-MS/MS). The soluble protein extract (SPE) at a concentration of 2.0 mg/mL displayed up to 80% of antibacterial activity against S. Typhimurium. Complete inhibition of L. monocytogenes was reached with up to 1.65 mg/mL of SPE. Plant protease extract containing ananain-like enzyme inhibited up to 90% against S. Typhimurium and up to 85% against L. monocytogenes using only 10 μg/mL of the partial-purified enzyme.

Purification and Biochemical Characterization of a New Protease Inhibitor from Conyza dioscoridis with Antimicrobial, Antifungal and Cytotoxic Effects

The main objective of the current study was the extraction, purification, and biochemical characterization of a protein protease inhibitor from Conyzadioscoridis. Antimicrobial potential and cytotoxic effects were also examined. The protease inhibitor was extracted in 0.1 M phosphate buffer (pH 6–7). Then, the protease inhibitor, named PDInhibitor, was purified using ammonium sulfate precipitation followed by filtration through a Sephadex G-50 column and had an apparent molecular weight of 25 kDa. The N-terminal sequence of PDInhibitor showed a high level of identity with those of the Kunitz family. PDInhibitor was found to be active at pH values ranging from 5.0 to 11.0, with maximal activity at pH 9.0. It was also fully active at 50 °C and maintained 90% of its stability at over 55 °C. The thermostability of the PDInhibitor was clearly enhanced by CaCl₂ and sorbitol, whereas the presence of Ca²⁺ and Zn²⁺ ions, Sodium taurodeoxycholate (NaTDC), Sodium dodecyl sulfate (SDS), Dithiothreitol (DTT), and β-ME dramatically improved the inhibitory activity. A remarkable affinity of the protease inhibitor with available important therapeutic proteases (elastase and trypsin) was observed. PDInhibitor also acted as a potent inhibitor of commercial proteases from Aspergillus oryzae and of Proteinase K. The inhibitor displayed potent antimicrobial activity against gram+ and gram- bacteria and against fungal strains. Interestingly, PDInhibitor affected several human cancer cell lines, namely HCT-116, MDA-MB-231, and Lovo. Thus, it can be considered a potentially powerful therapeutic agent.

Kunitz Proteinase Inhibitors Limit Water Stress Responses in White Clover (Trifolium repens L.) Plants

The response of plants to water deficiency or drought is a complex process, the perception of which is triggered at the molecular level before any visible morphological responses are detected. It was found that different groups of plant proteinase inhibitors (PIs) are induced and play an active role during abiotic stress conditions such as drought. Our previous work with the white clover (Trifolium repens L.) Kunitz Proteinase Inhibitor (Tr-KPI) gene family showed that Tr-KPIs are differentially regulated to ontogenetic and biotic stress associated cues and that, at least some members of this gene family may be required to maintain cellular homeostasis. Altered cellular homeostasis may also affect abiotic stress responses and therefore, we aimed to understand if distinct Tr-PKI members function during drought stress. First, the expression level of three Tr-KPI genes, Tr-KPI1, Tr-KPI2, and Tr-KPI5, was measured in two cultivars and one white clover ecotype with differing capacity to tolerate drought. The expression of Tr-KPI1 and Tr-KPI5 increased in response to water deficiency and this was exaggerated when the plants were treated with a previous period of water deficiency. In contrast, proline accumulation and increased expression of Tr-NCED1, a gene encoding a protein involved in ABA biosynthesis, was delayed in plants that experienced a previous drought period. RNAi knock-down of Tr-KPI1 and Tr-KPI5 resulted in increased proline accumulation in leaf tissue of plants grown under both well-watered and water-deficit conditions. In addition, increased expression of genes involved in ethylene biosynthesis was found. The data suggests that Tr-KPIs, particularly Tr-KPI5, have an explicit function during water limitation. The results also imply that the Tr-KPI family has different in planta proteinase targets and that the functions of this protein family are not solely restricted to one of storage proteins or in response to biotic stress.

An anti-infective synthetic peptide with dual antimicrobial and immunomodulatory activities

Antibiotic-resistant infections are predicted to kill 10 million people per year by 2050, costing the global economy $100 trillion. Therefore, there is an urgent need to develop alternative technologies. We have engineered a synthetic peptide called clavanin-MO, derived from a marine tunicate antimicrobial peptide, which exhibits potent antimicrobial and immunomodulatory properties both in vitro and in vivo. The peptide effectively killed a panel of representative bacterial strains, including multidrug-resistant hospital isolates. Antimicrobial activity of the peptide was demonstrated in animal models, reducing bacterial counts by six orders of magnitude, and contributing to infection clearance. In addition, clavanin-MO was capable of modulating innate immunity by stimulating leukocyte recruitment to the site of infection, and production of immune mediators GM-CSF, IFN-γ and MCP-1, while suppressing an excessive and potentially harmful inflammatory response by increasing synthesis of anti-inflammatory cytokines such as IL-10 and repressing the levels of pro-inflammatory cytokines IL-12 and TNF-α. Finally, treatment with the peptide protected mice against otherwise lethal infections caused by both Gram-negative and -positive drug-resistant strains. The peptide presented here directly kills bacteria and further helps resolve infections through its immune modulatory properties. Peptide anti-infective therapeutics with combined antimicrobial and immunomodulatory properties represent a new approach to treat antibiotic-resistant infections.

A 2S Albumin from the Seed Cake of Ricinus communis Inhibits Trypsin and Has Strong Antibacterial Activity against Human Pathogenic Bacteria

Hospital-acquired infections caused by antibiotic-resistant bacteria threaten the lives of many citizens all over the world. Discovery of new agents to hinder bacterial development would have a significant impact on the treatment of infections. Here, the purification and characterization of Rc-2S-Alb, a protein that belongs to the 2S albumin family, from Ricinus communis seed cake, are reported. Rc-2S-Alb was purified after protein extraction with Tris-HCl buffer, pH 7.5, fractionation by ammonium sulfate (50-75%), and chromatography on Phenyl-Sepharose and DEAE-Sepharose. Rc-2S-Alb, a 75 kDa peptide, displays trypsin inhibitory activity and has high in vitro antibacterial activity against Bacillus subtilis, Klebsiella pneumonia, and Pseudomonas aeruginosa, which are important human pathogenic bacteria. Atomic force microscopy studies indicated that Rc-2S-Alb disrupts the bacterial membrane with loss of the cytoplasm content and ultimately bacterial death. Therefore, Rc-2S-Alb is a powerful candidate for the development of an alternative drug that may help reduce hospital-acquired infections.

Antimicrobial Activity of ILTI, a Kunitz-Type Trypsin Inhibitor from Inga laurina (SW.) Willd

Over the last few years, a growing number of proteinase inhibitors have been isolated from plants and particularly from seeds and have shown antimicrobial activity. A 20,000 Da serine peptidase inhibitor, named ILTI, was isolated from Inga laurina seeds and showed potent inhibitory enzymatic activity against trypsin. The aim of this study was to determine the effects of ILTI on the growth of pathogenic and non-pathogenic microorganisms. We observed that ILTI strongly inhibited in particular the growth of Candida tropicalis and Candida buinensis, inducing cellular agglomeration. However, it was ineffective against human pathogenic bacteria. We also investigated the potential of ILTI to permeabilize the plasma membrane of yeast cells. C. tropicalis and C. buinensis were incubated for 24 h with the ILTI at different concentrations, which showed that this inhibitor induced changes in the membranes of yeast cells, leading to their permeabilization. Interestingly, ILTI induced the production of reactive oxygen species (ROS) in C. tropicalis and C. buinensis cells. Finally, ILTI was coupled with fluorescein isothiocyanate, and subsequent treatment of C. tropicalis and C. buinensis with DAPI revealed the presence of the labeled protein in the intracellular spaces. In conclusion, our results indicated the ability of peptidase inhibitors to induce microbial inhibition; therefore, they might offer templates for the design of new antifungal agents.

Knock-down of transcript abundance of a family of Kunitz proteinase inhibitor genes in white clover (Trifolium repens) reveals a redundancy and diversity of gene function

The transcriptional regulation of four phylogenetically distinct members of a family of Kunitz proteinase inhibitor (KPI) genes isolated from white clover (Trifolium repens; designated Tr-KPI1, Tr-KPI2, Tr-KPI4 and Tr-KPI5) has been investigated to determine their wider functional role. The four genes displayed differential transcription during seed germination, and in different tissues of the mature plant, and transcription was also ontogenetically regulated. Heterologous over-expression of Tr-KPI1, Tr-KPI2, Tr-KPI4 and Tr-KPI5 in Nicotiana tabacum retarded larval growth of the herbivore Spodoptera litura, and an increase in the transcription of the pathogenesis-related genes PR1 and PR4 was observed in the Tr-KPI1 and Tr-KPI4 over-expressing lines. RNA interference (RNAi) knock-down lines in white clover displayed significantly altered vegetative growth phenotypes with inhibition of shoot growth and a stimulation of root growth, while knock-down of Tr-KPI1, Tr-KPI2 and Tr-KPI5 transcript abundance also retarded larval growth of S. litura. Examination of these RNAi lines revealed constitutive stress-associated phenotypes as well as altered transcription of cellular signalling genes. These results reveal a functional redundancy across members of the KPI gene family. Further, the regulation of transcription of at least one member of the family, Tr-KPI2, may occupy a central role in the maintenance of a cellular homeostasis.

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.

Purification and characterization of a stable Kunitz trypsin inhibitor from Trigonella foenum-graecum (fenugreek) seeds

Kunitz trypsin inhibitor was purified from the seeds of Trigonella foenum-graecum (TfgKTI) belonging to fabaceae family by ammonium sulphate precipitation, cation exchange, gel filtration and hydrophobic chromatography. Purity of the protein was analyzed by RP-HPLC and native-PAGE. SDS-PAGE analysis under reducing and non-reducing conditions showed that protein consists of a single polypeptide chain with molecular mass of approximately 20 kDa. Mass spectroscopy analysis revealed that the intact mass of purified inhibitor is 19,842.154 Da. One dimensional SDS gel was tryptically digested, resulting peptides were subjected to MALDI-TOF-MS analysis, and peptide mass fingerprinting (PMF) analysis of TfgKTI shows sequence similarity with Kunitz trypsin inhibitor in database search. Two dimensional electrophoresis identified presence of four isoinhibitors (pI values of 5.1, 5.4, 5.7 and 6.1). Kinetic studies showed that the protein is a competitive inhibitor and has high binding affinity with trypsin (Ki 3.01×10(-9)M) and chymotrypsin (Ki 0.52×10(-9)M). The TfgKTI retained the inhibitory activity over a broad range of pH (pH 3-10), temperature (37-100°C) and salt concentration (up to 3.5%). Far-UV circular dichroism measurements revealed that TfgKTI is predominantly composed of β-sheets (39%) and unordered structures (48%) with slight helical content (13%). TfgKTI retained over 90% trypsin inhibition upon storage at 4°C for over a period of six months.

Characterization and pharmacological properties of a novel multifunctional Kunitz inhibitor from Erythrina velutina seeds

Inhibitors of peptidases isolated from leguminous seeds have been studied for their pharmacological properties. The present study focused on purification, biochemical characterization and anti-inflammatory and anticoagulant evaluation of a novel Kunitz trypsin inhibitor from Erythrina velutina seeds (EvTI). Trypsin inhibitors were purified by ammonium sulfate (30-60%), fractionation followed by Trypsin-Sepharose affinity chromatography and reversed-phase high performance liquid chromatography. The purified inhibitor showed molecular mass of 19,210.48 Da. Furthermore, a second isoform with 19,228.16 Da was also observed. The inhibitor that showed highest trypsin specificity and enhanced recovery yield was named EvTI (P2) and was selected for further analysis. The EvTI peptide fragments, generated by trypsin and pepsin digestion, were further analyzed by MALDI-ToF-ToF mass spectrometry, allowing a partial primary structure elucidation. EvTI exhibited inhibitory activity against trypsin with IC50 of 2.2×10(-8) mol.L(-1) and constant inhibition (Ki) of 1.0×10(-8) mol.L(-1), by a non-competitive mechanism. In addition to inhibit the activity of trypsin, EvTI also inhibited factor Xa and neutrophil elastase, but do not inhibit thrombin, chymotrypsin or peptidase 3. EvTI was investigated for its anti-inflammatory and anti-coagulant properties. Firstly, EvTI showed no cytotoxic effect on human peripheral blood cells. Nevertheless, the inhibitor was able to prolong the clotting time in a dose-dependent manner by using in vitro and in vivo models. Due to anti-inflammatory and anticoagulant EvTI properties, two sepsis models were here challenged. EvTI inhibited leukocyte migration and specifically acted by inhibiting TNF-α release and stimulating IFN-α and IL-12 synthesis. The data presented clearly contribute to a better understanding of the use of Kunitz inhibitors in sepsis as a bioactive agent capable of interfering in blood coagulation and inflammation.

Inhibitory effects of a Kunitz-type inhibitor from Pithecellobium dumosum (Benth) seeds against insect-pests' digestive proteinases

Pithecellobium dumosum is a tree belonging to the Mimosoideae subfamily that presents various previously characterized Kunitz-type inhibitors. The present study provides a novel Kunitz-trypsin inhibitor isoform purified from P. dumosum seeds. Purification procedure was performed by TCA precipitation followed by a trypsin-Sepharose chromatography and a further reversed-phase HPLC. Purified inhibitor (PdKI-4) showed enhanced inhibitory activity against bovine trypsin and chymotrypsin. Furthermore, PdKI-4 showed remarkable inhibitory activity against serine proteases from the coleopterans Callosobruchus maculatus and Zabrotes subfasciatus, and the lepidopterans Alabama argillacea and Telchin licus. However, PdKI-4 was unable to inhibit porcine pancreatic elastase, pineapple bromelain and Carica papaya papain. SDS-PAGE showed that PdKI-4 consisted of a single polypeptide chain with molecular mass of 21 kDa. Kinetic studies demonstrated that PdKI-4 is probably a competitive inhibitor with a Ki value of 5.7 × 10(-10) M for bovine trypsin. PdKI-4 also showed higher stability over a wide range of temperature (37-100 °C) and pH (2-12). N-termini sequence was obtained by Edman degradation showing higher identity with other Mimosoideae subfamily Kunitz-type inhibitor members. In summary, data here reported indicate the biotechnological potential of PdKI-4 for development of products against insect-pests.

Cn-AMP1: a new promiscuous peptide with potential for microbial infections treatment

The antimicrobial peptides (AMPs) are evolutionarily ancient molecules that act as components of the innate immune system. Recently, it was demonstrated that a single AMP can perform various functions; this ability is known as "peptide promiscuity." However, little is known about promiscuity in plant AMPs without disulfide bonds. This study was carried out to evaluate the promiscuity of Cn-AMP1: a promising disulfide-free plant peptide with reduced size and cationic and hydrophobic properties. Its activity against human pathogenic bacteria and fungal pathogens, as well as its in vitro immunostimulatory activity and effects on cancerous and healthy mammalian cell proliferation were studied here. Cn-AMP1 exerts antimicrobial effects against Gram-positive bacteria, Gram-negative bacteria, and fungi. Moreover, tumor cell viability activity in Caco-2 cells, as well as immunostimulatory activity by evaluating upregulated inflammatory-cytokine secretion by monocytes was also positively observed. Cn-AMP1 does not exhibit a well-defined conformation in aqueous solution and probably undergoes a 3(10)-helix transition in hydrophobic environments. The experimental results support the promiscuous activity of Cn-AMP1, presenting a wide range of activities, including antibacterial, antifungal, and immunostimulatory activity. In the future, Cn-AMP1 should be used in the development of novel biopharmaceuticals, mainly due to its reduced size and broad spectrum of activity.