Characterization of a Kunitz-type serine protease inhibitor from Solanum tuberosum having lectin activity

Optimization of caseinolytic and coagulating activities of Solanum tuberosum rennets for cheese making

BACKGROUND

In recent years, the rising global demand for cheese, the high cost and limited supply of calf rennet, and consumer choices have increased research into new alternatives to animal or recombinant chymosins for cheese making. Plant proteases with caseinolytic activity (CA) and milk-clotting activity (MCA) have been proposed as alternatives for milk clotting to obtain artisanal cheeses with new organoleptic properties. They have been named vegetable rennets (vrennets). The aim of this study was to evaluate the performance of two Solanum tuberosum aspartic proteases (StAP1 and StAP3) as vrennets for cheese making and to obtain a statistical model that could predict and optimize their enzymatic activity.

RESULTS

To optimize the CA and MCA activities, a response surface methodology was used. Maximum values of CA and MCA for both enzymes were found at pH 5.0 and 30-35 °C. Analysis of the degradation of casein subunits showed that it is possible to tune the specificity of both enzymes by changing the pH. At pH 6.5, the αS - and β- subunit degradation is reduced while conserving a significant MCA.

CONCLUSION

The statistical models obtained in this work showed that StAP1 and StAP3 exert CA and MCA under pH and temperature conditions compatible with those used for cheese making. The casein subunit degradation percentages obtained also allowed us to select the best conditions for the degradation of the κ-casein subunit by StAPs. These results suggest that StAP1 and StAP3 are good candidates as vrennets for artisan cheese making. © 2023 Society of Chemical Industry.

Partial characterization of purified glycoprotein from nutshell of Arachis hypogea L. towards macrophage activation and leishmaniacidal activity

Arachis hypogea L. protein fraction-2 (AHP-F2) from the Peanut shell was extracted and characterized and its potent immunomodulatory and anti-leishmanial role was determined in this present study. AHP-F2 was found to be a glycoprotein as the presence of carbohydrates were confirmed by the analysis of high-performance liquid chromatography (HPLC) yielded glucose, galactose, mannose, and xylose. AHP-F2 molecular mass was found to be ∼28 kDa as indicated in MALDI-TOF and peptide mass fingerprinting analysis followed by Mascot search. The peptide matches revealed the similarity of the mannose/glucose binding lectin with 71.07% in the BLAST analysis. After that, the 3D structure of the AHP-F2 model was designed and validated by the Ramachandran plot. The immunomodulatory role of AHP-F2 was established in murine peritoneal macrophages as induction of nitric oxide (NO), and stimulation of proinflammatory cytokines (IL-12 and IFN-γ) in a dose-dependent manner was observed. Interestingly, it was also found that AHP-F2 has interacted with the innate immune receptor, toll-like receptors (TLRs) as established in molecular docking as well as mRNA expression. The anti-leishmanial potential of AHP-F2 was revealed with a prominent inhibition of amastigote growth within the murine macrophages with prompt induction of nitrite release. Altogether, the isolated AHP-F2 from Arachis hypogea L. has strong immunomodulatory and anti-leishmanial potential which may disclose a new path to treat leishmaniasis.

Plant lectin: A promising future anti-tumor drug

Since the early discovery of plant lectins at the end of the 19th century, and the finding that they could agglutinate erythrocytes and precipitate glycans from their solutions, many applications and biological roles have been described for these proteins. Later, the observed erythrocytes clumping features were attributed to the lectin-cell surface glycoconjugates recognition. Neoplastic transformation leads to various cellular alterations which impact the growth of the cell and its persistence, among which is the mutation in the outer surface glycosylation signatures. Quite a few lectins have been found to act as excellent biomarkers for cancer diagnosis while some were presented with antiproliferative activity that initiated by lectin binding to the respective glycocalyx receptors. These properties are blocked by the hapten sugar that is competing for the lectin affinity binding site. In vitro investigations of lectin-cancer cell's glycocalyx interactions lead to a series of immunological reactions that result in autophagy or apoptosis of the transformed cells. Mistletoe lectin, an agglutinin purified from the European Viscum album is the first plant lectin employed in the treatment of cancer to enter into the clinical trial phases. The entrapment of lectin in nanoparticles besides other techniques to promote bioavailability and stability have also been recently studied. This review summarizes our up-to-date understanding of the future applications of plant lectins in cancer prognosis and diagnosis. With the provision of many examples of lectins that exhibit anti-neoplastic properties.

Anti-epileptic Kunitz-like peptides discovered in the branching coral Acropora digitifera through transcriptomic analysis

Approximately 50 million people are suffering from epilepsy worldwide. Corals have been used for treating epilepsy in traditional Chinese medicine, but the mechanism of this treatment is unknown. In this study, we analyzed the transcriptome of the branching coral Acropora digitifera and obtained its Kyoto Encyclopedia of Genes and Genomes (KEGG), EuKaryotic Orthologous Groups (KOG) and Gene Ontology (GO) annotation. Combined with multiple sequence alignment and phylogenetic analysis, we discovered three polypeptides, we named them AdKuz1, AdKuz2 and AdKuz3, from A. digitifera that showed a close relationship to Kunitz-type peptides. Molecular docking and molecular dynamics simulation indicated that AdKuz1 to 3 could interact with GABA_A receptor but AdKuz2-GABA_A remained more stable than others. The biological experiments showed that AdKuz1 and AdKuz2 exhibited an anti-inflammatory effect by decreasing the aberrant level of nitric oxide (NO), IL-6, TNF-α and IL-1β induced by LPS in BV-2 cells. In addition, the pentylenetetrazol (PTZ)-induced epileptic effect on zebrafish was remarkably suppressed by AdKuz1 and AdKuz2. AdKuz2 particularly showed superior anti-epileptic effects compared to the other two peptides. Furthermore, AdKuz2 significantly decreased the expression of c-fos and npas4a, which were up-regulated by PTZ treatment. In addition, AdKuz2 reduced the synthesis of glutamate and enhanced the biosynthesis of gamma-aminobutyric acid (GABA). In conclusion, the results indicated that AdKuz2 may affect the synthesis of glutamate and GABA and enhance the activity of the GABA_A receptor to inhibit the symptoms of epilepsy. We believe, AdKuz2 could be a promising anti-epileptic agent and its mechanism of action should be further investigated.

Characterization of a Bowman-Birk type trypsin inhibitor purified from seeds of Solanum surattense

A Bowman-Birk type trypsin inhibitor protein (SSTI) from seeds of the medicinal plant Solanum surattense was isolated, purified and characterized. SSTI showed a single band on SDS-PAGE corresponding to 11.4 kDa molecular weight. It is a glycoprotein (2.8% glycosylation) that differentially interacted with trypsin and chymotrypsin in a concentration-dependent manner. Its peptide sequence is similar to other Bowman-Birk type protease inhibitors found in Glycine max and Phaseolus acutifolius. The inhibitory activity was stable over a wide range of pH (1-10) and temperatures (10-100° C). Far-UV Circular Dichroism (CD) studies showed that SSTI contains β sheets (~ 23%) and α helix (~ 6%) and demonstrated structural stability at wide pH and high temperature. The kinetic analysis revealed a noncompetitive (mixed) type nature of SSTI and low inhibitor constant (Ki) values (16.6 × 10-8 M) suggested strong inhibitory activity. Isothermal titration calorimetric analysis revealed its high affinity towards trypsin with dissociation constant (Kd) 2.28 µM.

ApSerpin-ZX from Agapanthus praecox, is a potential cryoprotective agent to plant cryopreservation

Cryopreservation-induced cell death is regarded as an important problem faced by cryobiologists. Oxidative stress and programmed cell death are detrimental to cell survival. Serine protease inhibitors (serpins) inhibit pro-cell-death proteases and play a pro-survival role in excessive cell death induced by abiotic stress. In this study, ApSerpin-ZX was isolated from Agapanthus praecox and characterized as a protective protein in plant cryopreservation. The mRNA level of ApSerpin-ZX was elevated under abiotic stress, such as salt, osmosis, oxidative, cold, and cryoinjury. The purified recombinant protein expressed in E. coli was added to the plant vitrification solution and used for A. praecox embryogenic callus cryopreservation. The concentration of 0.6-4.8 mg∙L^-1 of ApSerpin-ZX protein was beneficial to the survival of cryopreserved embryogenic callus of A. praecox. The most effective concentration was 1.2 mg∙L^-1, which elevated the survival by 37.15%. Subsequently, the cryopreservation procedure with 1.2 mg∙L^-1 of ApSerpin-ZX protein was regarded as the treated group, compared to standard procedure, to determine the physiological mechanism of ApSerpin-ZX protein on cryopreserved cell. The MDA and H₂O₂ contents were significantly decreased in the treated group, along with reduced OH· generation activity in the recovery stage. After the addition of ApSerpin-ZX, the POD and CAT activities keep increased, while SOD activity increased only after dehydration. Besides, the caspase-1-like and caspase-3-like activities were lower than the standard procedure. This study indicated that ApSerpin-ZX was a potential cryoprotective agent that alleviated oxidative stress and cell death induced by cryopreservation.

Trypsin inhibitor from Enterolobium contortisiliquum seeds impairs Aedes aegypti development and enhances the activity of Bacillus thuringiensis toxins

BACKGROUND

Disease vector insects are barriers for human development. The use of synthetic chemicals to control these vectors has caused damage to the environment and contributed to the arising of resistant insect populations. This has led to an increased search for plant-derived molecules with insecticidal activity or that show synergistic effects with known insecticidal substances, such as protease inhibitors. Thus, we aimed to evaluate the effect of Enterolobium contortisiliquum trypsin inhibitor (EcTI) on Aedes aegypti development as well as its effect on insecticidal activity of Bacillus thuringiensis toxins.

RESULTS

EcTI showed an apparent molecular mass about of 20 kDa in SDS-PAGE and was able to inhibit in vitro the activity of trypsin and proteases from midgut of Ae. aegypti larvae. EcTI was not able to cause acute toxicity on mosquito larvae even at 1000 μg mL^-1 , however it promoted a delay in larval development after prolonged exposure. The zymogram results for EcTI-treated larvae (from 50 to 200 μg mL^-1 ) showed an increase of midgut proteases activity as a larvae defense mechanism, however no changes in the enzyme profile was observed. These same concentrations were able to enhance up to three fold the insecticidal activity of B. thuringiensis toxins without causing toxicity to Artemia sp. nauplii, a non-target organism.

CONCLUSIONS

The results offer a novel approach by combining EcTI and B. thuringiensis toxins for combating Ae. aegypti larvae. © 2020 Society of Chemical Industry.

Effects of a Reserve Protein on Spodoptera frugiperda Development: A Biochemical and Molecular Approach to the Entomotoxic Mechanism

Talisin is a storage protein from Talisia esculenta seeds that presents lectin-like and peptidase inhibitor properties. These characteristics suggest that talisin plays a role in the plant defense process, making it a multifunctional protein. This work aimed to investigate the effects of chronic intake of talisin on fifth instar larvae of Spodoptera frugiperda, considered the main insect pest of maize and the cause of substantial economic losses in several other crops. The chronic intake of talisin presented antinutritional effects on the larvae, reducing their weight and prolonging the total development time of the insects. In addition, talisin-fed larvae also showed a significant reduction in the activity of trypsin-like enzymes. Midgut histology analysis of talisin-fed larvae showed alterations in the intestinal epithelium and rupture of the peritrophic membrane, possibly causing an increase of aminopeptidase activity in the midgut lumen. Talisin also proved to be resistant to degradation by the digestive enzymes of S. frugiperda. The transcription profile of trypsin, chymotrypsin and aminopeptidase genes was also analyzed through qPCR technique. Talisin intake resulted in differential expression of at least two genes from each of these classes of enzymes. Molecular docking studies indicated a higher affinity of talisin for the less expressed enzymes.

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.

The impact of four processing methods on trypsin-, chymotrypsin- and alpha-amylase inhibitors present in underutilised legumes

The global trend in increasing plant-based protein diets due to health and ideological reasons, has created an increased demand for food legumes that exceeds current production. To meet this demand, it is timely to reduce relying solely on soybean, and explore the potential of the underutilised legumes that are cultivated regionally. Underutilised legumes are rich in protein, carbohydrates and other nutrients that are essential for consumer. However, relatively little is known about their anti-nutritional properties and processing methods. Anti-nutritional factors (ANFs) such as enzyme inhibitors are prevalent in legumes and may interfere with digestibility and nutrient absorption. Nevertheless, an optimised food processing method will overcome this challenge and warrant a safe inclusion of legume in plant-based protein diets. Hence current study aimed to optimise the food processing methods (soaking, wet heating, autoclaving and freezing) and evaluate their efficiency in eliminating the enzyme inhibitors [trypsin, chymotrypsin (CIA) and α-amylase (AIA) inhibitors] present in seven underutilised legumes. Current study showed that autoclaving at 121 °C for 15 min reduced the AIA in all underutilised legumes tested. The AIA and CIA of bambara groundnut were successfully inactivated by wet heating at 50 °C for 60 min, and by autoclaving at 121 °C for 15 min. While the CIA of chickpea was successfully inactivated by freezing at - 80 °C for 24 h.