Imbibition of soybean seeds in warm water results in the release of copious amounts of Bowman-Birk protease inhibitor, a putative anticarcinogenic agent

Effect of conventional and novel techniques on extraction yield, chemical characterisation and biological activities of proteins from bitter gourd (Momordica charantia)

The study investigates the effect of conventional and novel extraction techniques on the protein extraction yield from bitter gourd seeds (Momordica charantia). Ultrasound assisted-extraction (UAE) treatment for 30 min at 4 °C using a 20 kHz ultrasound probe resulted in the highest extraction yield of crude proteins. After purification, 9.08 ± 0.23 g of protein with 82.69 ± 0.78% purity was obtained from 100 g of M. charantia seeds on a dry basis. Mass spectrometry identified proteins with reported antidiabetic activity. Antidiabetic assays showed significantly higher antidiabetic activity for the purified protein (81.10 ± 2.64%) compared to the crude protein (32.59 ± 2.76%). In vitro cytotoxicity analysis showed minimal cytotoxicity levels at concentrations <200 μg.mL-1. Overall, UAE was effective to obtain crude protein from M. charantia seeds and a subsequent purification step enhanced antidiabetic activity. However, further research is required to demonstrate in-vivo antidiabetic activity.

Determination of protease inhibitors, glycinin, and beta-conglycinin in soybeans and their relationships

In order to search for suitable soybean varieties for different applications, the protein contents of Kunitz trypsin inhibitor (KTI), Bowman-Birk trypsin inhibitor (BBI), glycinin (11S), and β-conglycinin (7S) of 93 soybean samples from different sources and harvest years were quantified by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Meanwhile, the protease inhibitory activities against trypsin and chymotrypsin were determined. Results showed that the individual protein contents and trypsin inhibitor activities differed significantly (p < 0.05) among soybean samples. KTI contents ranged from 5.25 to 14.60 mg·g-1 ; BBI contents ranged from 1.81 to 5.74 mg·g-1 ; 11S varied from 13.65% to 48.55% and 7S varied from 15.68% to 42.15% of total soluble protein; trypsin and chymotrypsin inhibitory activities were 8.93-20.95 mg TI·g-1 and 4.18 -12.79 mg CI·g-1 , respectively. Excellent linear relationships existed between trypsin inhibitor contents and their activities. The regression equations offer a rapid method for estimating the activity of KTI or BBI in raw soybeans. PRACTICAL APPLICATION: The regression equations established based on a large number of soybean varieties offered a rapid method to estimate the activity of trypsin inhibitors. The data presented here provided useful information for the food industry or breeders to select soybean varieties with different inhibitory activities or protein contents for different food processing applications.

Soybean proteins/peptides: A review on their importance, biosynthesis, vacuolar sorting, and accumulation in seeds

Soybean is one of the most important sources of plant protein and is known for its wide range of agricultural, food, and industrial applications as well as health benefits. Interest in soybean proteins has been steadily growing as progressively more applications and benefits are discovered. This review article is focused on the major seed storage proteins of soybean, their three-dimensional structures, their nutritional importance and bioactive peptides, cellular synthesis, and accumulation in seeds. This will also summarize past efforts in the recombinant production of foreign proteins or bioactive peptides in soybean seed.

Basic 7S globulin in plants

Soybean seed basic 7S globulin (Bg7S)-like proteins are found in many plant species. Bg7S was originally thought to be a major seed storage protein but was later found to be multifunctional, with stress response, antibacterial activity, hormone receptor-like activity. Moreover, functional differences between Bg7S proteins from legumes and other plants have been revealed. In non-leguminous plants, Bg7S molecules inhibit the invasion of pathogenic microorganisms. However, although leguminous plants have a peptide called leg-insulin that can bind to Bg7S, non-leguminous plants do not have leginsulin. Bg7S in leguminous plants and other plants may have evolved in functionally different directions. Several homologs of Bg7S in plants are reported, but there is no homolog of this protein in peas, suggesting that the pea evolution might have followed a different route when compared to other leguminous plants. Although the functions of Bg7S are well documented in plants, recent studies suggest that this protein is also important in controlling blood glucose level, blood pressure and plasma cholesterol level, and cancer cell antiproliferative actions.

Insights into the Role of Tick Salivary Protease Inhibitors during Ectoparasite-Host Crosstalk

Protease inhibitors (PIs) are ubiquitous regulatory proteins present in all kingdoms. They play crucial tasks in controlling biological processes directed by proteases which, if not tightly regulated, can damage the host organism. PIs can be classified according to their targeted proteases or their mechanism of action. The functions of many PIs have now been characterized and are showing clinical relevance for the treatment of human diseases such as arthritis, hepatitis, cancer, AIDS, and cardiovascular diseases, amongst others. Other PIs have potential use in agriculture as insecticides, anti-fungal, and antibacterial agents. PIs from tick salivary glands are special due to their pharmacological properties and their high specificity, selectivity, and affinity to their target proteases at the tick-host interface. In this review, we discuss the structure and function of PIs in general and those PI superfamilies abundant in tick salivary glands to illustrate their possible practical applications. In doing so, we describe tick salivary PIs that are showing promise as drug candidates, highlighting the most promising ones tested in vivo and which are now progressing to preclinical and clinical trials.

Inhibition of Protease and Egg Hatching of Haemonchus contortus by Soybean Seed Exudates

Gastrointestinal nematode infection of small ruminants causes losses in livestock production. Plant compounds show promises as alternatives to commercial anthelmintics that have been exerting selective pressures that lead to the development of drug-resistant parasites. Soybean (Glycine max) is an economical value crop, with a higher protein content compared to other legumes. The objective of this study was to evaluate whether the protease inhibitors exuded from the G. max mature seeds have anthelmintic activity against Haemonchus contortus. To obtain the soybean exudates (SEX), mature seeds were immersed in 100 mM sodium acetate buffer, pH 5.0, at 10 C, for 24 hr. Then the naturally released substances present in SEX were collected and exhaustively dialyzed (cutoff 12 kDa) against distilled water. The dialyzed seed exudates (SEXD) were heated at 100 C for 10 min and centrifuged (12,000 g, at 4 C for 15 min). The supernatant obtained was recovered and designated as the heat-treated exudate fraction (SEXDH). The protein content, protease inhibitor activity, and the effect of each fraction on H. contortus egg hatch rate were evaluated. The inhibition extent of SEX, SEXD, and SEXDH on H. contortus egg proteases was 31.1, 42.9, and 63.8%, respectively. Moreover, SEX, SEXD, and SEXDH inhibited the egg hatching with EC50 of 0.175, 0.175, and 0.241 mg ml-1, respectively. Among the commercial protease inhibitors tested, only EDTA and E-64 inhibited the H. contortus hatch rate (79.0 and 28.9%, respectively). We present evidence demonstrating that soybean exudate proteins can effectively inhibit H. contortus egg hatching. This bioactivity is displayed by thermostable proteins and provides evidence that protease inhibitors are a potential candidate for anthelmintic use.

Bowman-Birk Inhibitors: Insights into Family of Multifunctional Proteins and Peptides with Potential Therapeutical Applications

Bowman-Birk inhibitors (BBIs) are found primarily in seeds of legumes and in cereal grains. These canonical inhibitors share a highly conserved nine-amino acids binding loop motif CTP1SXPPXC (where P1 is the inhibitory active site, while X stands for various amino acids). They are natural controllers of plants' endogenous proteases, but they are also inhibitors of exogenous proteases present in microbials and insects. They are considered as plants' protective agents, as their elevated levels are observed during injury, presence of pathogens, or abiotic stress, i.a. Similar properties are observed for peptides isolated from amphibians' skin containing 11-amino acids disulfide-bridged loop CWTP1SXPPXPC. They are classified as Bowman-Birk like trypsin inhibitors (BBLTIs). These inhibitors are resistant to proteolysis and not toxic, and they are reported to be beneficial in the treatment of various pathological states. In this review, we summarize up-to-date research results regarding BBIs' and BBLTIs' inhibitory activity, immunomodulatory and anti-inflammatory activity, antimicrobial and insecticidal strength, as well as chemopreventive properties.

Effect of high-temperature, short-time cooking conditions on in vitro protein digestibility, enzyme inhibitor activity and amino acid profile of selected legume grains

African yam beans (Sphenostylis stenocarpa), Bambara groundnut (Vigna subterranean) and Pigeon pea (Cajanus cajan) flours were extruded in a single screw extruder at two extrusion temperatures; 100 °C and 140 °C, and the effect of extrusion cooking temperature on the chemical composition; crude protein, crude fibre, ether extract and nitrogen-free extracts, protein digestibility, enzyme inhibitor activity and amino acid profiles was investigated. The crude protein, amino acid profile and ether extract of the grain legumes were negatively affected (p < 0.05) by the extrusion cooking process, with a significant increase in nitrogen-free extracts for all grain legumes, and increased crude fibre of Bambara groundnut and Pigeon pea extrudates. Extrusion cooking of African yam beans and Pigeon pea produced extrudates with significantly lower trypsin, chymotrypsin and amylase inhibitor activity as well as improved protein digestibility. However, extrusion cooking did not modify the chymotrypsin and amylase inhibitor activity of Bambara groundnut extrudates. Extrusion cooking at 140 °C compared to 100 °C significantly reduced the protein quality of extrudates resulting in 22.94-51.27%, 5.11-25.18%, and 7.78-38.42% reduction in amino acid concentration of African yam beans, Bambara groundnut and Pigeon pea, respectively.

Integrated Proteomics and Metabolomics Analysis Highlights Correlative Metabolite-Protein Networks in Soybean Seeds Subjected to Warm-Water Soaking

Soaking of soybean seeds is a prerequisite for the production of soy foods, and it has been shown that the extent of water absorbed during different imbibition conditions directly affects the quality of the subsequent soybean seed products by yet unknown mechanisms. In order to elucidate the molecular changes in soybean seeds during different soaking temperatures, we performed an integrated proteomics and metabolomics analysis of seeds soaked at 4, 25, and 55 °C. Proteomics analysis revealed that various enzymes related to carbohydrate and protein hydrolysis were activated in soybean seeds during water soaking at 55 °C. Interestingly, results obtained from this integrated proteomics and metabolomics study showed changes in various metabolites, including isoflavones, amino acids, and sugars, that were positively correlated with proteome changes occurring upon soaking at 55 °C. Furthermore, soaking of soybean seeds at 55 °C resulted in degradation of indigestible anti-nutrients such as raffinose oligosaccharides. Taken together, our results suggest that the seed soaking at a high temperature (55 °C) increases the nutritional value of soybean seeds by decreasing the contents of some of the common anti-nutrients.

Metabolic Profiling-Based Evaluation of the Fermentative Behavior of Aspergillus oryzae and Bacillus subtilis for Soybean Residues Treated at Different Temperatures

Soybean processing, e.g., by soaking, heating, and fermentation, typically results in diverse metabolic changes. Herein, multivariate analysis-based metabolic profiling was employed to investigate the effects of fermentation by Aspergillus oryzae or Bacillus subtilis on soybean substrates extracted at 4, 25, or 55 °C. As metabolic changes for both A. oryzae and B. subtilis were most pronounced for substrates extracted at 55 °C, this temperature was selected to compare the two microbial fermentation strategies, which were shown to be markedly different. Specifically, fermentation by A. oryzae increased the levels of most organic acids, γ-aminobutyric acid, and glutamine, which were ascribed to carbohydrate metabolism and conversion of glutamic acid into GABA and glutamine. In contrast, fermentation by B. subtilis increased the levels of most amino acids and isoflavones, which indicated the high activity of proteases and β-glucosidase. Overall, the obtained results were concluded to be useful for the optimization of processing steps in terms of nutritional preferences.

Effects of water absorption of soybean seed on the quality of soymilk and the release of flavor compounds

The water absorption of soybeans during soaking is directly related to the quality characteristics and the flavor properties of soybeans for processing. In this paper, the effects of water absorption of soybean seed on the quality of soymilk and the release of flavor compounds were investigated during soaking at 4 °C, 25 °C, and 50 °C at different pH values. The results showed that the water absorption rate increased as the soaking temperature and pH increased, while the equilibrium value was relatively stable. Peleg's equation with good fitting of the absorption kinetics was used to predict the hydration characteristics of undehulled soybean. MALDI-TOF/TOF-MS results showed that the major released proteins are basic 7S globulin, which is released in large amounts at high temperature. The water absorption of soybean seed significantly enhanced the extraction yields of protein, fat and solids of the prepared soymilk, and alkaline soaking pH further promoted the extraction of proteins and solids. A high soaking temperature can significantly decrease the required soaking time; however, it is unfavorable to the extraction yields of fat, proteins and solids, as well as the whiteness values and the particle sizes. The beany odor compounds of soymilk mainly consisted of hexanal, trans-2-hexenal, 1-octene-3-ol, hexanol, and 2-pentylfuran, and their contents were positively correlated with soaking temperature. A good balance of soymilk quality and flavor compound release can be achieved with soaking conditions of 25 °C and pH 9.

The water absorption of soybeans during soaking is directly related to the quality characteristics and the flavor properties of soybeans for processing.

Trypsin Inhibitors from Cajanus cajan and Phaseolus limensis Possess Antioxidant, Anti-Inflammatory, and Antibacterial Activity

Protease inhibitors are one of the most promising and investigated subjects for their role in pharmacognostic and pharmacological studies. This study aimed to investigate antioxidant, anti-inflammatory, and antimicrobial activities of trypsin inhibitors (TIs) from two plant sources (Cajanus cajan and Phaseolus limensis). TI was purified from C. cajan (PUSA-992) by ammonium sulfate precipitation followed by ion exchange chromatography. TI from Phaseolus limensis (lima bean trypsin inhibitor; LBTI) was procured from Sigma-Aldrich, St. Louis, Missouri, United States. The antioxidant activity was analyzed by ferric ion reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH). The anti-inflammatory property of TIs was determined by inhibition of albumin denaturation assay. Ascorbic acid and aspirin were used as standards for antioxidant and anti-inflammatory assays, respectively. These TIs were tested against various bacterial and fungal strains. The TIs showed DPPH radical-scavenging activity in a concentration-dependent manner with IC₅₀ values comparable to ascorbic acid. The FRAP values were also observed comparable to ascorbic acid and followed the trend of dose-dependent manner. The half maximal inhibitory concentration (IC₅₀) values of CCTI and LBTI in anti-inflammatory test showed that LBTI is more potent than CCTI. The TIs showed potent antibacterial activity, but apparently no action against fungi. This study has reported the biological properties of CCTI and LBTI for the first time. The results show that TIs possess the ability to inhibit diseases caused by oxidative stress, inflammation, and bacterial infestation.

Heat-induced inactivation mechanism of soybean Bowman-Birk inhibitors

Due to the complications of the soymilk system, the heat-induced Bowman-Birk inhibitor (BBI) inactivation mechanism is not well known. In this study, two BBI samples with low and high purities were prepared from soymilk. It was confirmed that three groups (A, C, and D) of BBI, which are contained in soybean seeds, were transferred into soymilk during processing. On heating, it was found that 1) the two subdomains of BBI were not equally heat stable, 2) the conformation of BBI gradually changed, 3) some amino acid residues (namely, cystine, serine and lysine) in BBI were degraded, 4) BBI did not tend to form intermolecular cross-links with another BBI, but did slightly with non-BBI proteins. Based on some previous studies, the conformational change of BBI was attributed to β-elimination reactions on the amino acid residues of BBI and the subsequent intramolecular reactions induced by the products yielded by the β-elimination reactions.

BG-4, a novel anticancer peptide from bitter gourd (Momordica charantia), promotes apoptosis in human colon cancer cells

Momordica charantia is a perennial plant with reported health benefits. BG-4, a novel peptide from Momordica charantia, was isolated, purified and characterized. The trypsin inhibitory activity of BG-4 is 8.6 times higher than purified soybean trypsin inhibitor. The high trypsin inhibitory activity of BG-4 may be responsible for its capability to cause cytotoxicity to HCT-116 and HT-29 human colon cancer cells with ED₅₀ values of 134.4 and 217.0 μg/mL after 48 h of treatment, respectively. The mechanism involved in the cytotoxic effect may be associated with induction of apoptosis as evidenced by increased percentage of HCT-116 and HT-29 colon cancer cells undergoing apoptosis from 5.4% (untreated) to 24.8% (BG-4 treated, 125 μg/mL for 16 h) and 8.5% (untreated) to 31.9% (BG-4 treated, 125 μg/mL for 16 h), respectively. The molecular mechanistic explanation in the apoptosis inducing property of BG-4 is due to reduced expression of Bcl-2 and increased expression of Bax leading to increased expression of caspase-3 and affecting the expression of cell cycle proteins p21 and CDK2. This is the first report on the anti-cancer potential of a novel bioactive peptide isolated from Momordica charantia in vitro supporting the potential therapeutic property of BG-4 against colon cancer that must be addressed using in vivo models of colon carcinogenesis.

Characterization, biomedical and agricultural applications of protease inhibitors: A review

This review describes Protease Inhibitors (PIs) which target or inhibit proteases, protein digesting enzymes. These proteases play a crucial task in many biological events including digestion, blood coagulation, apoptosis etc. Regardless of their crucial roles, they need to be checked regularly by PIs as their excess may possibly damage host organism. On basis of amino acid composition of PIs where Protease-PI enzymatic reactions occur i.e. serine, cysteine, and aspartic acid, they are classified. Nowadays, various PIs are being worked upon to fight various parasitic or viral diseases including malaria, schistosomiasis, colds, flu', dengue etc. They prevent an ongoing process begun by carcinogen exposure by keeping a check on metastasis. They also possess potential to reduce carcinogen-induced, increased levels of gene amplification to almost normal levels. Some PIs can principally be used for treatment of hypertension and congestive heart failure by blocking conversion of angiotensin I to angiotensin II for example Angiotensin-converting enzyme inhibitors (ACEIs). Also PIs target amyloid β-peptide (Aβ) level in brain which is prime responsible for development of Alzheimer's Disease (AD). Also, PIs inhibit enzymatic activity of HIV-1 Protease Receptor (PR) by preventing cleavage events in Gag and Gag-Pol that result in production of non-virulent virus particles.

Recombinant Buckwheat Trypsin Inhibitor Induces Mitophagy by Directly Targeting Mitochondria and Causes Mitochondrial Dysfunction in Hep G2 Cells

Mitochondria are essential targets for cancer chemotherapy and other disease treatments. Recombinant buckwheat trypsin inhibitor (rBTI), a member of the potato type I proteinase inhibitor family, was derived from tartary buckwheat extracts. Our results showed that rBTI directly targeted mitochondria and induced mitochondrial fragmentation and mitophagy. This occurs through enhanced depolarization of the mitochondrial membrane potential, increasing reactive oxygen species (ROS) generation associated with the rise of the superoxide dismutase and catalase activity and glutathione peroxidase (GSH) content, and changes in the GSH/oxidized glutathione ratio. Mild and transient ROS induced by rBTI were shown to be important signaling molecules required to induce Hep G2 mitophagy to remove dysfunctional mitochondria. Furthermore, rBTI could directly induce mitochondrial fragmentation. It was also noted that rBTI highly increased colocalization of mitochondria in treated cells compared to nontreated cells. Tom 20, a subunit of the translocase of the mitochondrial outer membrane complex responsible for recognizing mitochondrial presequences, may be the direct target of rBTI.

Proteome of Soybean Seed Exudates Contains Plant Defense-Related Proteins Active against the Root-Knot Nematode Meloidogyne incognita

Several studies have described the effects of seed exudates against microorganisms, but only few of them have investigated the proteins that have defensive activity particularly against nematode parasites. This study focused on the proteins released in the exudates of soybean seeds and evaluated their nematicidal properties against Meloidogyne incognita. A proteomic approach indicated the existence of 63 exuded proteins, including β-1,3-glucanase, chitinase, lectin, trypsin inhibitor, and lipoxygenase, all of which are related to plant defense. The presence of some of these proteins was confirmed by their in vitro activity. The soybean exudates were able to reduce the hatching of nematode eggs and to cause 100% mortality of second-stage juveniles (J2). The pretreatment of J2 with these exudates resulted in a 90% reduction of the gall number in tobacco plants. These findings suggest that the exuded proteins are directly involved in plant defense against soil pathogens, including nematodes, during seed germination.

Identification of a new soybean kunitz trypsin inhibitor mutation and its effect on bowman-birk protease inhibitor content in soybean seed

Soybean seed contains antinutritional compounds that inactivate digestive proteases, principally corresponding to two families: Kunitz trypsin inhibitors (KTi) and Bowman-Birk inhibitors (BBI). High levels of raw soybean/soybean meal in feed mixtures can cause poor weight gain and pancreatic abnormalities via inactivation of trypsin/chymotrypsin enzymes. Soybean protein meal is routinely heat-treated to inactivate inhibitors, a practice that is energy-intensive and costly and can degrade certain essential amino acids. In this work, we screened seed from 520 soybean accessions, using a combination of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblots with anti-Kunitz trypsin inhibitor antibodies. A soybean germplasm accession was identified with a mutation affecting an isoform annotated as nonfunctional (KTi1), which was determined to be synergistic with a previously identified mutation (KTi3-). We observed significant proteome rebalancing in all KTi mutant lines, resulting in dramatically increased BBI protein levels.

Differential expression and elution behavior of basic 7S globulin among cultivars under hot water treatment of soybean seeds

Basic 7S globulin (Bg7S), which accumulates in mature soybean (Glycine max) seeds, is an extracellular matrix protein. A large amount of Bg7S is synthesized de novo and is eluted from soybean seeds when immersed in 50-60°C water (hot water treatment, HWT). However, the Bg7S elution mechanism remains unclear. Under HWT, the seeds probably undergo heat stress and flooding stress. To obtain fundamental knowledge related to how Bg7S is eluted from hot-water-treated seeds, this study compared Bg7S elution among soybean cultivars having different flooding tolerance during pre-germination. The amounts of Bg7S eluted from seeds varied significantly among cultivars. Elution was suppressed by seed coats regarded as preventing the leakage of seed contents by rapid water imbibition. Furthermore, Bg7S expression levels differed among cultivars, although the difference did not result from any variation in Bg7S promoter sequences. However, the expression levels of Bg7S under HWT were not associated with the flooding tolerance level. Immunoelectron microscopy revealed that the Bg7S accumulated in the intercellular space of hot-water-treated seeds. Plasma membrane shrinkage was observed. The main proteins eluted from seeds under HWT were located in the extracellular space. This study clarified the mechanism of Bg7S elution from seeds under HWT.

Rhizoma Pinelliae trypsin inhibitor separation, purification and inhibitory activity on the proliferation of BGC-823 gastric adenocarcinoma cells

The aim of this study was to isolate and purify Rhizoma Pinelliae trypsin inhibitor (RPTI), determine its N-terminal amino acid sequence and evaluate its inhibitory effect on the proliferation of poorly differentiated BGC-823 human gastric adenocarcinoma cells. RPTI was separated and purified from a 40% (NH₄)₂SO₄ precipitate of crude protein extract of Pinellia ternata tuber using affinity chromatography with trypsin as the ligand. The N-terminal amino acid sequence of RPTI was determined using the Edman degradation method. The inhibitory effect of RPTI on BGC-823 cell proliferation was detected in vitro using the MTT method and in vivo in tumour-bearing mice. The purified RPTI showed a single band under SDS-PAGE, its molecular weight was 14 kDa and its N-terminal amino acid sequence was DPVVDG. RPTI inhibited trypsin activity, with an inhibition ratio of 1:6.78 (mass). RPTI significantly inhibited the proliferation of BGC-823 cells in vitro. The IC₅₀ of RPTI was 16.96 μg/ml within 48 h after treatment and 9.61 μg/ml within 72 h after treatment. Subcutaneous injection of RPTI around the tumour significantly inhibited BGC-823 tumour growth in mice. The tumour inhibitory effect was concentration- and dose-dependent. RPTI did not significantly influence the spleen coefficient of the mice. In conclusion, RPTI is a serine proteinase inhibitor with antitumour activity.