CgTI, a novel thermostable Kunitz trypsin-inhibitor purified from Cassia grandis seeds: Purification, characterization and termiticidal activity

A new trypsin inhibitor from Centrosema plumieri effective against digestive proteases from Tribolium castaneum, an eco-friendly alternative

Tribolium castaneum, also known as the red flour beetle, is a polyphagous pest that seriously damages agricultural products, including stored and processed grains. Researchers have aimed to discover alternative pest control mechanisms that are less harmful to the ecosystem than those currently used. We conduct the purification and characterization of a protease inhibitor from C. plumieri seeds and an in vitro evaluation of its insecticidal potential against the insect pest T. castaneum. The trypsin inhibitor was isolated from C. plumieri seeds in a single-step DEAE-Sepharose column chromatography and had a molecular mass of 50 kDA. When analyzed for interaction with different proteolytic enzymes, the inhibitor exhibited specificity against trypsin and no activity against other serine proteases such as chymotrypsin and elastase-2. The isolated inhibitor was able to inhibit digestive enzymes of T. castaneum from extracts of the intestine of this insect. Therefore, we conclude that the new protease inhibitor, specific in tryptic inhibition, of protein nature from the seeds of C. plumieri was effective in inhibiting the digestive enzymes of T. castaneum and is a promising candidate in the ecological control of pests.

Novel Stable Protease Inhibitor from Phoenix dactylifera(L.) Flowers with Antimicrobial and Antitumoral Activities

A novel protease inhibitor isolated from date palm Phoenix dactylifera(L.) flowers (PIDF) was purified and characterized. A heat and acidic treatment step followed by ethanol precipitation and reverse-phase high-performance chromatography was applied to purify this natural protease inhibitor to homogeneity with a single band of about 19 kDa. The stability study depicted that PIDF was fully stable at 40 °C and retained 65% of its initial activity after heating at 50 °C for 24 h. Its thermal stability at 70 °C was markedly enhanced by adding calcium, bovine serum albumin, and sorbitol as well as by metal divalent cations, especially Mg2+ and Hg2+. This protease inhibitor showed high inhibitory activity against therapeutic proteases, including pepsin, trypsin, chymotrypsin, and collagenase, and acted as a potent inhibitor of some commercial microbial proteases from Aspergillus oryzae, Bacillus. sp, and Bacillus licheniformis. Moreover, a potent antibacterial spectrum against Gram (+) and Gram (-) bacterial strains and an efficient antifungal effect were observed. Its cytotoxicity toward human colorectal cancer cell LoVo and HCT-116 lines suggested that PIDF could serve as a new therapeutic target inhibiting human colorectal cancer.

Development of a rapid process for purification of Bowman-Birk and Kunitz inhibitors from legume seeds, and evaluation of their biophysical, insecticidal, and antimicrobial properties

Bowman-Birk inhibitor (BBI ~10 kDa) and Kunitz inhibitor (KI ~20 kDa) are serine protease/proteinase inhibitor(s) [PI(s)] ubiquitously found in several Leguminous plant species with insecticidal and therapeutic properties. Due to narrow molecular mass differences, the separation of these inhibitors from a single seed variety is tedious. The present study is aimed to develop a rapid protocol (<24 h) for purifying BBI and KI from legume seeds using mild trichloroacetic acid (TCA) extraction followed by trypsin-affinity chromatography. The mature seeds of Vigna radiata and Cajanus platycarpus are used as a model to purify BBI and KI using this protocol. The BBI and KI purified from the seeds of V. radiata are labeled as VrBBI & VrKI, and C. platycarpus are labeled as CpBBI & CpKI, respectively. These PIs are confirmed by immunodetection and MALDI-TOF studies and further characterized for their structural (CD & fluorescence spectroscopy) and functional properties (temperature & DTT stability). BBI(s) purified using the above process are effective in the management of castor semi-looper 'Achaea janata', while KI(s) are effective in the management of pod borer 'Helicoverpa armigera'. Besides, both BBI(s) and KI(s) have significant potential in controlling the growth of methicillin-sensitive 'Staphylococcus aureus', a gram-positive pathogenic bacterium.

Plant Kunitz Inhibitors and Their Interaction with Proteases: Current and Potential Pharmacological Targets

The action of proteases can be controlled by several mechanisms, including regulation through gene expression; post-translational modifications, such as glycosylation; zymogen activation; targeting specific compartments, such as lysosomes and mitochondria; and blocking proteolysis using endogenous inhibitors. Protease inhibitors are important molecules to be explored for the control of proteolytic processes in organisms because of their ability to act on several proteases. In this context, plants synthesize numerous proteins that contribute to protection against attacks by microorganisms (fungi and bacteria) and/or invertebrates (insects and nematodes) through the inhibition of proteases in these organisms. These proteins are widely distributed in the plant kingdom, and are present in higher concentrations in legume seeds (compared to other organs and other botanical families), motivating studies on their inhibitory effects in various organisms, including humans. In most cases, the biological roles of these proteins have been assigned based mostly on their in vitro action, as is the case with enzyme inhibitors. This review highlights the structural evolution, function, and wide variety of effects of plant Kunitz protease inhibitors, and their potential for pharmaceutical application based on their interactions with different proteases.

TcTI, a Kunitz-type trypsin inhibitor from cocoa associated with defense against pathogens

Protease inhibitors (PIs) are important biotechnological tools of interest in agriculture. Usually they are the first proteins to be activated in plant-induced resistance against pathogens. Therefore, the aim of this study was to characterize a Theobroma cacao trypsin inhibitor called TcTI. The ORF has 740 bp encoding a protein with 219 amino acids, molecular weight of approximately 23 kDa. rTcTI was expressed in the soluble fraction of Escherichia coli strain Rosetta [DE3]. The purified His-Tag rTcTI showed inhibitory activity against commercial porcine trypsin. The kinetic model demonstrated that rTcTI is a competitive inhibitor, with a Ki value of 4.08 × 10-7 mol L-1. The thermostability analysis of rTcTI showed that 100% inhibitory activity was retained up to 60 °C and that at 70-80 °C, inhibitory activity remained above 50%. Circular dichroism analysis indicated that the protein is rich in loop structures and β-conformations. Furthermore, in vivo assays against Helicoverpa armigera larvae were also performed with rTcTI in 0.1 mg mL-1 spray solutions on leaf surfaces, which reduced larval growth by 70% compared to the control treatment. Trials with cocoa plants infected with Mp showed a greater accumulation of TcTI in resistant varieties of T. cacao, so this regulation may be associated with different isoforms of TcTI. This inhibitor has biochemical characteristics suitable for biotechnological applications as well as in resistance studies of T. cacao and other crops.

Structural modelling and thermostability of a serine protease inhibitor belonging to the Kunitz-BPTI family from the Rhipicephalus microplus tick

rBmTI-A is a recombinant serine protease inhibitor that belongs to the Kunitz-BPTI family and that was cloned from Rhipicephalus microplus tick. rBmTI-A has inhibitory activities on bovine trypsin, human plasma kallikrein, human neutrophil elastase and plasmin with dissociation constants in nM range. It is characterized by two inhibitory domains and each domain presents six cysteines that form three disulfide bonds, which contribute to the high stability of its structure. Previous studies suggest that serine protease inhibitor rBmTI-A has a protective potential against pulmonary emphysema in mice and anti-inflammatory potential. Besides that, rBmTI-A presented a potent inhibitory activity against in vitro vessel formation. In this study, the tertiary structure of rBmTI-A was modeled. The structure stabilization was evaluated by molecular dynamics analysis. Circular dichroism spectroscopy data corroborated the secondary structure found by the homology modelling. Also, in circular dichroism data it was shown a thermostability of rBmTI-A until approximately 70 °C, corroborated by inhibitory assays toward trypsin.

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.

Purification, cDNA cloning and characterization of Kunitz-type protease inhibitors from Apios americana tubers

Two kinds of Kunitz-type protease inhibitors, AKPI1 and AKPI2, were purified from Apios americana tubers by four steps of column chromatographies and their cDNA cloning was performed. AKPI1 cDNA consist of 809 nucleotides, and the matured protein had 190 amino acids with 20,594 Da. AKPI2 cDNA consist of 794 nucleotides, and the matured protein had 177 amino acids with 19,336 Da. P1 site of AKPI2 was Leu88, suggested the target enzyme was chymotrypsin. On the other hand, Gly85-Ile86-Ser87 was positioned around P1 site of AKTI1. Sequence analysis suggested that two forms (single-chain and two-chain form) of AKPI2 protein were present in the tubers. Recombinant AKPI2 expressed by E.coli system showed inhibitory activity toward serine proteases and heat stability. The Ki values toward chymotrypsin and trypsin were 4 × 10^-7 M and 6 × 10^-6 M, respectively.Abbreviations: AAL: Apios americana lectin; AATI: Apios americana Bowman-Birk type trypsin inhibitor; ACE: angiotensin-converting enzyme; IPTG: isopropyl-β-D-thio-galactopyranoside; Ki: inhibition constant; KPIs: Kunitz-type protease inhibitors; L-BAPA: Benzoyl-L-arginine p-nitroanilide monohydrochloride; L-BTPA: Benzoyl-L-tyrosine p-nitroanilide; PFLNA: Pyr-Phe-Leu-p-nitroanilide; RP-HPLC: reverse-phase high-performance liquid chromatography; RT-PCR: reverse transcription-polymerase chain reaction; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; SLIC: sequence and ligation independent cloning; STANA: N-Succinyl-Ala-Ala-Ala-p-nitroanilide; SHR: spontaneously hypertensive rats; TFA: trifluoroacetic acid; UTR: untranslated region.