Trypsin inhibitor content and activity of soaking water whey as waste in soy milk processing

Soybean soaking water whey (SWW) is obtained as the waste of soy milk production and mostly represents an environmental problem. The aim of this study was to assess the content of proteins and content and activity of trypsin inhibitors of fresh SWW, obtained during soy milk production. Two zones of Bowman-Birk trypsin inhibitors (BBI) were detected. One was identified as a monomeric form of BBI (0.61-2.93%) and the other one was identified as a polymeric form of BBI (0.45-3.33%). The degree of BBI extraction (1.88-5.49%) was influenced by the soybean genotype and the grain size, i.e. it increased with increasing grain size. Kunitz trypsin inhibitor was not detected. Total proteins were found in traces in SWW (0.03-0.06%). Low residual trypsin inhibitor activity (0.32-0.55%) suggested that SWW can potentially be applied for preparing food or feed. In that case it will not be waste but a cheap functional supplement with BBI as a biologically active component.

In vivo anti-inflammatory efficacy of the combined Bowman-Birk trypsin inhibitor and genistein isoflavone, two biological compounds from soybean

Soybean Bowman-Birk protease inhibitor (BBI) and genistein, two biological compounds from soybean, are well-known for their anti-inflammatory, antioxidant, and anticancer activities. The aim of this study was designing a BBI-genistein conjugate and then investigating its protective effect on lipopolysaccharide (LPS)-induced inflammation in BALB/c mice, compared with the effects of combination of BBI and genistein. BBI was purified from soybean and the BBI-genistein conjugate was synthesized. The BALB/c mice were intraperitoneally treated 2 hours before LPS induction. Our results showed that treatment with the combination of BBI and genistein greatly led to more reduced serum levels of tumor necrosis factor (TNF)-α and interferon (IFN)-γ compared with the treatments of BBI alone, the BBI-genistein conjugate, and genistein alone, respectively. Moreover, the expression of TNF-α and IFN-γ in the splenocytes was significantly downregulated along with improving host survival against the LPS-induced lethal endotoxemia in the same way. Our data support a new combined therapy using BBI and genistein, as natural anti-inflammatory agents, to develop a new drug for inflammatory diseases.

Lathyrus sativus Originating from Different Geographical Regions Reveals Striking Differences in Kunitz and Bowman-Birk Inhibitor Activities

Grass pea (Lathyrus sativus L.) is an important legume commonly grown in arid and semi-arid regions. This protein-rich legume performs well even under harsh environmental conditions and is considered to be a strategic famine food in developing countries. Unfortunately, its potential usage is greatly limited as a result of the presence of antinutritional factors, including the neuroexcitatory amino acid β-N-oxalyl-l-α,β-diaminopropionic acid (β-ODAP) and protease inhibitors. β-ODAP is responsible for a neurodegenerative syndrome that results in the paralysis of lower limbs, while protease inhibitors affect protein digestibility, resulting in reduced growth. Concerted research efforts have led to development of grass pea cultivars with reduced β-ODAP content. In contrast, very little information is available on the protease inhibitors of L. sativus. In this study, we have conducted biochemical characterization of 51 L. sativus accessions originating from different geographical regions. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analyses of seed globulins and prolamins revealed striking similarity in their protein profile, although geographic-specific variations in profiles was also evident. Measurement of Bowman-Birk chymotrypsin inhibitor (BBi) and Kunitz trypsin inhibitor (KTi) activities in accessions revealed striking differences among them. Amino acid sequence alignment of grass pea BBi and KTi revealed significant homology to protease inhibitors from several legumes. Real-time polymerase chain reaction analysis demonstrated high-level expression of BBi and KTi in dry seeds and weak expression in other organs. Our study demonstrates substantial variation in BBi and KTi among grass pea accessions that could be exploited in breeding programs for the development of grass pea lines that are devoid of these antinutritional factors.

Purification and characterization of Bowman-Birk and Kunitz isoinhibitors from the seeds of Rhynchosia sublobata (Schumach.) Meikle, a wild relative of pigeonpea

Rhynchosia sublobata, a wild relative of pigeonpea, possesses defensive proteinase/protease inhibitors (PIs). Characterization of trypsin specific PIs (RsPI) separated from seeds by column chromatography using 2-D gel electrophoresis and Edman degradation method identified R. sublobata possessed both Bowman-Birk isoinhibitors (RsBBI) and Kunitz isoinhibitors (RsKI). A quick method was developed to separate RsBBI and RsKI from RsPI based on their differential solubility in TCA and acetate buffer. N-terminus sequencing of RsBBI and RsKI by MALDI-ISD ascertained the presence of Bowman Birk and Kunitz type isoinhibitors in R. sublobata. RsBBI (9216 Da) and RsKI (19,412 Da) exhibited self-association pattern as revealed by western blotting with anti-BBI antibody and MALDI-TOF peptide mass fingerprint analysis, respectively. RsBBI and RsKI varied significantly in their biochemical, biophysical and insecticidal properties. RsBBI inhibited the activity of trypsin (Ki = 128.5 ± 4.5 nM) and chymotrypsin (Ki = 807.8 ± 23.7 nM) while RsKI (Ki = 172.0 ± 9.2 nM) inhibited the activity of trypsin alone, by non-competitive mode. The trypsin inhibitor (TI) and chymotrypsin inhibitor (CI) activities of RsBBI were stable up to 100 °C. But, RsBBI completely lost its TI and CI activities on reduction with 3 mM DTT. Conversely, RsKI lost its TI activity on heating at 100 °C and retained >60% of its TI activity in presence of 3 mM DTT. CD spectroscopic studies on RsBBI and RsKI showed their secondary structural elements in the following order: random coils > β-sheets/β-turns > α-helix. However, RsKI showed reversible denaturation midpoint (Tm) of 75 °C. Further, the significant inhibitory activity of RsBBI (IC₅₀ = 24 ng) and RsKI (IC₅₀ = 59 ng) against trypsin-like gut proteases of Achaea janata (AjGPs) and Helicoverpa armigera (HaGPs) suggest them as potential biomolecules in the management of A. janata and H. armigera, respectively.

Biochemical properties of a bacterially-expressed Bowman-Birk inhibitor from Rhynchosia sublobata (Schumach.) Meikle seeds and its activity against gut proteases of Achaea janata

Crude proteinase inhibitors (CPIs) extracted from the seeds of Rhynchosia sublobata, a wild relative of pigeon pea showed pronounced inhibitory activity on the larval gut trypsin-like proteases of lepidopteran insect pest - Achaea janata. Consequently, a full-length cDNA of Bowman-Birk inhibitor gene (RsBBI1) was cloned from the immature seeds of R. sublobata. It contained an ORF of 360 bp encoding a 119-amino acid polypeptide (13.3 kDa) chain with an N-terminus signal sequence comprising of 22 amino acids. The amino acid sequence and phylogenetic analysis together revealed that RsBBI1 exhibited a close relation with BBIs from soybean and Phaseolus spp. A cDNA sequence corresponding to RsBBI1 mature protein (89 amino acid stretch) was expressed in E. coli. The recombinant rRsBBI1 protein with a molecular mass of 9.97 kDa was purified using trypsin affinity chromatography. The purified rRsBBI1 exhibited non-competitive mode of inhibition of both bovine trypsin (Ki of 358 ± 11 nM) and chymotrypsin (Ki of 446 ± 9 nM). Its inhibitory activity against these proteases was stable at high temperatures (>95 °C) and a wide pH range but sensitive to reduction with dithiothreitol (DTT), indicating the importance of disulphide bridges in exhibiting its activity. Also, rRsBBI1 showed significant inhibitory activity (IC₅₀ = 70 ng) on A. janata larval gut trypsin-like proteases (AjGPs). Conversely, it showed <1% inhibitory activity (IC₅₀ = 8 μg) on H. armigera larval gut trypsin-like proteases (HaGPs) than it has against AjGPs. Besides, in vivo feeding experiments clearly indicated the deleterious effects of rRsBBI1 on larval growth and development in A. janata which suggests it can be further exploited for such properties.

Protein Separation Coacervation with Carboxymethyl Cellulose of Different Substitution Degree: Noninteracting Behavior of Bowman-Birk Chymotrypsin Inhibitor

We first observed that protein/polysaccharide interaction exhibited noninteracting behavior which makes Bowman-Birk chymotrypsin inhibitor (BBI) always free of complexation, being separated from another protein with similar isoelectric points, Kunitz trypsin inhibitor (KTI). Turbidity titrations showed that the electrostatic attractions were much stronger between KTI/BBI (KBi) and carboxymethyl cellulose of higher substitution degree. Unchanged chymotrypsin inhibitory activity (CIA) indicated that BBI had negligible contribution to protein recovery and trypsin inhibitory activity (TIA). Tricine-SDS-PAGE revealed that, at r = 20:1-2:1, unbound BBI was left in the supernatant when bound KTI transferred into precipitates, even if there was excess negative charge. Thus, purified KTI or BBI was achieved easily at the given conditions. The noninteracting behavior of BBI was further confirmed by ITC, where the binding enthalpy of BBI to CMC was negligible compared with the high binding affinity ( K_b) of KTI. This work will be beneficial to protein purification based on protein-polysaccharide coacervation.

Bowman-Birk inhibitors from legumes as colorectal chemopreventive agents

Aberrant functioning of serine proteases in inflammatory and carcinogenic processes within the gastrointestinal tract (GIT) has prompted scientists to investigate the potential of serine protease inhibitors, both natural and synthetic, as modulators of their proteolytic activities. Protease inhibitors of the Bowman-Birk type, a major protease inhibitor family in legume seeds, which inhibit potently and specifically trypsin- and chymotrypsin-like proteases, are currently being investigated as colorectal chemopreventive agents. Physiologically relevant amounts of Bowman-Birk inhibitors (BBI) can reach the large intestine in active form due to their extraordinary resistance to extreme conditions within the GIT. Studies in animal models have proven that dietary BBI from several legume sources, including soybean, pea, lentil and chickpea, can prevent or suppress carcinogenic and inflammatory processes within the GIT. Although the therapeutic targets and the action mechanism of BBI have not yet been elucidated, the emerging evidence suggests that BBI exert their preventive properties via protease inhibition; in this sense, serine proteases should be considered as primary targets in early stages of carcinogenesis. The validation of candidate serine proteases as therapeutic targets together with the identification, within the wide array of natural BBI variants, of the most potent and specific protease inhibitors, are necessary to better understand the potential of this protein family as colorectal chemopreventive agents.

Quantitative determination of active Bowman-Birk isoinhibitors, IBB1 and IBBD2, in commercial soymilks

Naturally-occurring serine protease inhibitors of the Bowman-Birk family exert their potential chemopreventive and/or therapeutic properties via protease inhibition. In this study, we have quantified the amounts of active BBI isoinhibitors, IBB1 and IBBD2, in six commercial soymilks. By using cation exchange chromatography, the BBI isoinhibitors were isolated and their specific trypsin inhibitory activity was used to estimate their amounts in soymilk samples. IBB1 and IBBD2 concentrations ranged from 0.44 to 5.20 and 0.27 to 4.60 mg/100ml of soymilk, respectively; total BBI, considered as the sum of both isoinhibitors, ranged from 0.60 to 9.07 mg/100ml of soymilk. These data show that physiologically relevant amounts of active BBI are present in commercial soymilk and may exert potential health-promoting effects.

Isolation of Bowman-Birk-Inhibitor from soybean extracts using novel peptide probes and high gradient magnetic separation

Soybean proteins offer exceptional promise in the area of cancer prevention and treatment. Specifically, Bowman-Birk Inhibitor (BBI) has the ability to suppress carcinogenesis in vivo, which has been attributed to BBI's inhibition of serine protease (trypsin and chymotrypsin) activity. The lack of molecular probes for the isolation of this protein has made it difficult to work with, limiting its progress as a significant candidate in the treatment of cancer. This study has successfully identified a set of novel synthetic peptides targeting the BBI, and has demonstrated the ability to bind BBI in vitro. One of those probes has been covalently immobilised on superparamagnetic microbeads to allow the isolation of BBI from soy whey mixtures in a single step. Our ultimate goal is the use of the described synthetic probe to facilitate the isolation of this potentially therapeutic protein for low cost, scalable analysis and production of BBI.

Probing the soybean Bowman-Birk inhibitor using recombinant antibody fragments

The nutritional and health benefits of soy protein have been extensively studied over recent decades. The Bowman-Birk inhibitor (BBI), derived from soybeans, is a double-headed inhibitor of chymotrypsin and trypsin with anticarcinogenic and anti-inflammatory properties, which have been demonstrated in vitro and in vivo. However, the lack of analytical and purification methodologies complicates its potential for further functional and clinical investigations. This paper reports the construction of anti-BBI antibody fragments based on the principle of protein design. Recombinant antibody (scFv and diabody) molecules targeting soybean BBI were produced and characterized in vitro (K(D)~1.10(-9) M), and the antibody-binding site (epitope) was identified as part of the trypsin-specific reactive loop. Finally, an extremely fast purification strategy for BBI from soybean extracts, based on superparamagnetic particles coated with antibody fragments, was developed. To the best of the authors' knowledge, this is the first report on the design and characterization of recombinant anti-BBI antibodies and their potential application in soybean processing.

Lunasin and Bowman-Birk protease inhibitor concentrations of protein extracts from enzyme-assisted aqueous extraction of soybeans

Lunasin and Bowman-Birk protease inhibitor (BBI) are two soybean peptides to which health-promoting properties have been attributed. Concentrations of these peptides were determined in skim fractions produced by enzyme-assisted aqueous extraction processing (EAEP) of extruded full-fat soybean flakes (an alternative to extracting oil from soybeans with hexane) and compared with similar extracts from hexane-defatted soybean meal. Oil and protein were extracted by using countercurrent two-stage EAEP of soybeans at 1:6 solids-to-liquid ratio, 50 °C, pH 9.0, and 120 rpm for 1 h. Protein-rich skim fractions were produced from extruded full-fat soybean flakes using different enzyme strategies in EAEP: 0.5% protease (wt/g extruded flakes) used in both extraction stages; 0.5% protease used only in the second extraction stage; no enzyme used in either extraction stage. Countercurrent two-stage protein extraction of air-desolventized, hexane-defatted soybean flakes was used as a control. Protein extraction yields increased from 66% to 89-96% when using countercurrent two-stage EAEP with extruded full-fat flakes compared to 85% when using countercurrent two-stage protein extraction of air-desolventized, hexane-defatted soybean flakes. Extruding full-fat soybean flakes reduced BBI activity. Enzymatic hydrolysis reduced BBI contents of EAEP skims. Lunasin, however, was more resistant to both enzymatic hydrolysis and heat denaturation. Although using enzymes in both EAEP extraction stages yielded the highest protein and oil extractions, reducing enzyme use to only the second stage preserved much of the BBI and Lunasin.

Bowman-Birk proteinase inhibitor from Cajanus cajan seeds: purification, characterization, and insecticidal properties

A red gram proteinase inhibitor (RgPI) was purified from red gram ( Cajanus cajan ) seeds by using ammonium sulfate precipitation and ion-exchange, affinity, and gel filtration chromatography. SDS-PAGE under nonreducing condition revealed two protein bands with molecular masses of approximately 8.5 and approximately 16.5 kDa corresponding to monomeric and dimeric forms of RgPI, respectively. Similarly, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry also confirmed the presence of dimer as well as other oligomeric forms: trimer, tetramer, and pentamer. Reduction of RgPI with dithiothreitol (DTT) led to the dissociation of the dimeric and oligomeric forms. Native-PAGE and two-dimensional gel electrophoresis indicated the existence of isoinhibitors with pI values of 5.95, 6.25, 6.50, 6.90, and 7.15, respectively. The MALDI-TOF-TOF mass spectrum and N-terminal sequence 'DQHHSSKACC' suggested that the isolated RgPI is a member of the Bowman-Birk inhibitor family. RgPI exhibited noncompetitive type inhibitory activity against bovine pancreatic trypsin and chymotrypsin, with inhibition constants of 292 and 2265 nM, respectively. It was stable up to a temperature of 80 degrees C and was active over a wide pH range between 2 and 12. However, reduction with DTT or 2-mercaptoethanol resulted in loss of inhibitory activity against trypsin and chymotrypsin. It also decreased the activity of larval midgut trypsin-like proteinases in Manduca sexta . Its insecticidal property was further confirmed by reduction in the growth and development of these larvae, when supplemented in the diet.

Identification and characterization of a Bowman-Birk inhibitor active towards trypsin but not chymotrypsin in Lupinus albus seeds

The paper describes the purification, structural characterization and inhibitory properties of a trypsin inhibitor from Lupinus albus L., a leguminous plant believed to be devoid of any protease inhibitor. The protein has been isolated by a newly set-up procedure and characterized by direct amino acid sequencing, MALDI-TOF mass spectroscopy and circular dichroism. Inhibitory properties toward bovine trypsin and chymotrypsin, as well as its thermal and pH stabilities, have been also assessed. The inhibitor is 63 amino acid long (Mr 6858; pI 8.22) and it is capable to inhibit two trypsin molecules simultaneously, with a Kd of 4.2+/-0.4 nM, but not chymotrypsin. BLAST search against UniProtKB/TrEMBL database indicates that the inhibitor belongs to the Bowman-Birk inhibitor (BBI) family. The interest in these serine-protease inhibitors arises from the ability to prevent or suppress carcinogen-induced transformation, as shown in various in vitro and in vivo model systems.

A Bowman-Birk trypsin inhibitor with antiproliferative activity from Hokkaido large black soybeans

A trypsin inhibitor, with an N-terminal sequence highly homologous to those of 8-kDa Bowman-Birk trypsin inhibitors, was isolated from the seeds of Hokkaido large black soybeans. The trypsin inhibitor was unadsorbed on SP-Sepharose but adsorbed on DEAE-cellulose and Mono Q. It inhibited proliferation in breast cancer (MCF-7) cells and hepatoma (Hep G2) cells with an IC50 of 35 and 140 microM, respectively. The trypsin inhibitory activity of the inhibitor was completely preserved after exposure to temperatures up to 100 degrees C for 30 min and to the pH range 2-13 for the same duration. The trypsin inhibitor inhibited HIV-1 reverse transcriptase with an IC50 of 38 microM, but was devoid of antifungal activity toward Fusarium oxysporum and Mycosphaerella arachidicola.

A Bacillus subtilis fusion protein system to produce soybean Bowman–Birk protease inhibitor

A fusion protein based expression system was developed in the Gram-positive bacterium Bacillus subtilis to produce the soybean Bowman-Birk protease inhibitor (sBBI). The N-terminus of the mature sBBI was fused to the C-terminus of the 1st cellulose binding domain linker (CBD linker) of the BCE103 cellulase (from an alkalophilic Bacillus sp.). The strong aprE promoter was used to drive the transcription of the fusion gene and the AprE signal sequence was fused to the mature BCE103 cellulase for efficient secretion of the fusion protein into the culture medium. It was necessary to use a B. subtilis strain deficient in nine protease genes in order to reduce the proteolytic degradation of the fusion protein during growth. The fusion protein was produced in shake flasks at concentrations >1g/L. After growth, the sBBI was activated by treatment with 2-mercaptoethanol to allow the disulfide bonds to form correctly. An economical and scalable purification process was developed to purify sBBI based on acid precipitation of the fusion protein followed by acid/heat cleavage of the fusion protein at labile Asp-Pro bonds in the CBD linker. If necessary, non-native amino acids at the N- and C-termini were trimmed off using glutamyl endopeptidase I. After purification, an average of 72 mg of active sBBI were obtained from 1L of culture broth representing an overall yield of 21% based on the amount of sBBI activated before purification.

Inhibitory properties and solution structure of a potent Bowman-Birk protease inhibitor from lentil (Lens culinaris, L) seeds

Bowman-Birk serine protease inhibitors are a family of small plant proteins, whose physiological role has not been ascertained as yet, while chemopreventive anticarcinogenic properties have repeatedly been claimed. In this work we present data on the isolation of a lentil (Lens culinaris, L., var. Macrosperma) seed trypsin inhibitor (LCTI) and its functional and structural characterization. LCTI is a 7448 Da double-headed trypsin/chymotrypsin inhibitor with dissociation constants equal to 0.54 nM and 7.25 nM for the two proteases, respectively. The inhibitor is, however, hydrolysed by trypsin in a few minutes timescale, leading to a dramatic loss of its affinity for the enzyme. This is due to a substantial difference in the kon and k*on values (1.1 microM-1.s-1 vs. 0.002 microM-1.s-1), respectively, for the intact and modified inhibitor. A similar behaviour was not observed with chymotrypsin. The twenty best NMR structures concurrently showed a canonical Bowman-Birk inhibitor (BBI) conformation with two antipodal beta-hairpins containing the inhibitory domains. The tertiary structure is stabilized by ion pairs and hydrogen bonds involving the side chain and backbone of Asp10-Asp26-Arg28 and Asp36-Asp52 residues. At physiological pH, the final structure results in an asymmetric distribution of opposite charges with a negative electrostatic potential, centred on the C-terminus, and a highly positive potential, surrounding the antitryptic domain. The segment 53-55 lacks the anchoring capacity found in analogous BBIs, thus rendering the protein susceptible to hydrolysis. The inhibitory properties of LCTI, related to the simultaneous presence of two key amino acids (Gln18 and His54), render the molecule unusual within the natural Bowman-Birk inhibitor family.

Biochemical characterization of an effective substrate and potent activators of CK2 copurified with Bowman-Birk-type proteinase inhibitor from soybean seeds in vitro

By means of Mono P column chromatography, an effective phosphate acceptor (EPA) of casein kinase 2 (CK2) was purified from the Bowman-Birk-type proteinase inhibitor (BBI) fraction of soybean seeds. The most acidic EPA (aEPA, pI=approx. 3.7) was heavily phosphorylated when incubated with CK2 and 5 microM [gamma-(32)P]ATP in the presence of poly-Arg (a CK2 activator) in vitro. However, aEPA was slightly phosphorylated by casein kinase 1 (CK1) as effective as C-kinase and not at all by A-kinase in vitro. The 13 N-terminal amino acid residues (SDHSSSDDESSKP) of aEPA were 100% homologous to the corresponding sequence of soybean BBI-type proteinase inhibitor CII (SBI CII). Polyamine at 3 mM stimulated 4.6-fold the CK2-mediated phosphorylation of aEPA, and this phosphorylation was sensitive to quercetin (ID(50)=approx. 0.1 microM) in vitro. Furthermore, two basic proteins [Mr=29,000 (p29) and 17,000 (p17)] copurified with BBI were identified as proteolytic cleavage products of basic 7S globulin and functioned as potent CK2 activators in vitro. aEPA fully phosphorylated by CK2 in the presence of poly-Arg or basic proteins formed a complex with trypsin, whereas unphosphorylated aEPA was digested by trypsin in vitro. These results suggest that (i) aEPA (a BBI isoform) may coexist with two basic proteins (p29 and p17) generated from basic 7S globulin; and (ii) the physiological interaction between aEPA and its binding trypsin-like proteinases may be regulated through specific phosphorylation of aEPA by CK2 activated with the two basic proteins in legume seeds.

Anticarcinogenic Bowman Birk inhibitor isolated from snail medic seeds (Medicago scutellata): solution structure and analysis of self-association behavior

The high-resolution three-dimensional structure of a Bowman Birk inhibitor, purified from snail medic seeds (Medicago scutellata) (MSTI), has been determined in solution by 1H NMR spectroscopy at pH 5.6 and 27 degrees C. The structure of MSTI comprises two distinct symmetric domains each composed of a three-stranded beta-sheet containing a VIb type loop, where the active sites are located. A characteristic geometry of three aromatic residues confers stability to this protein, and we observe that this feature is conserved in all the Bowman Birk inhibitors of known structure. The two active domains exhibit different conformational features: the second domain displays higher flexibility and hydrophobicity with respect to the first one, and these properties have been correlated to a lower trypsin inhibitory specificity, in agreement with titration studies that have shown a stoichiometric ratio MSTI:trypsin of 1:1.5. NMR analysis indicated that MSTI undergoes self-association at concentrations higher than 2 mM, and the residues involved in this mechanism are localized at opposite faces of the molecule, having the highest positive and negative potential, respectively, thus indicating that electrostatic intermolecular interactions are the driving forces for MSTI association. Most of the residues affected by self-association are highly conserved in BBIs from different seeds, suggesting a functional relevance for these charged superficial patches, possibly involved in the interaction with other enzymes or macromolecules, thus triggering anti-carcinogenic activity.

Toxicity to the pea aphid Acyrthosiphon pisum of anti-chymotrypsin isoforms and fragments of Bowman-Birk protease inhibitors from pea seeds

Aphids feed on a protein-poor diet and are insensitive to several serine protease inhibitors. However, among the Bowman-Birk family of plant trypsin inhibitors (BBI), some members display significant toxicity to the pea aphid Acyrthosiphon pisum. A BBI isoform purified from pea seeds (PsTI-2) displays an IC50 of 41 microM and a LC50 of 48 microM at 7 days. Our data show that the chymotrypsin-directed active site from these bifunctional inhibitors is responsible for this activity, and that artificial cyclic peptides bearing the Bowman-Birk anti-chymotrypsin head induce much greater toxicity and growth inhibition than their anti-trypsin counterparts. The toxic syndrome included a rapid behavioural response of aphids on diets containing the toxic peptides, with induced restlessness after only 1 h of exposure to the chymotrypsin inhibitor. Nevertheless, chymotrypsin activity was not detected in aphid guts, using two chromogenic chymotrypsin substrates, and the physiological target of the chymotrypsin inhibitor remains unknown. These data show for the first time that plant chymotrypsin inhibitors, still widely unexplored, may act as paradoxical toxicants to aphids and serve as defensive metabolites for phloem-feeding insects.

Soybean bowman--birk inhibitor conjugates with clinical dextran. synthesis and antiproteolytic activity

Conjugates of the classical soybean Bowman-Birk inhibitor (BBI) with clinical dextran were synthesized. Clinical dextran was preliminarily oxidized with periodate to dialdehydedextran (DAD). The effect of the degree of oxidation of DAD on coupling of the inhibitor was evaluated. The binding of the protein was shown to increase with increasing degree of DAD oxidation (5, 10, 20%). Total coupling of the inhibitor occurred when the degree of oxidation of the dextran was 20%. The BBI-DAD (20%) conjugate contained 13% protein with BBI/DAD molar ratio 1 : 1. The conjugates retained the ability to inhibit trypsin (Ki = 0.2-0.3 nM) and alpha-chymotrypsin (Ki = 15-30 nM). Thus, the coupling of BBI with the polymeric carrier caused practically no decrease in the antiproteolytic activity of the inhibitor.

Isolation and characterization of soybean Bowman-Birk inhibitor from different sources

A chromatographic procedure for isolation of different isoforms of Bowman--Birk soybean trypsin inhibitors was developed. The number of isoforms was shown to depend on soybean cultivar. The amount of the classical Bowman--Birk inhibitor (BBI) in different soybean cultivars, commercial flour, and processing products was analyzed. BBI reaches its highest concentration in freshly milled seeds. Storage conditions optimum for preservation of maximum inhibitory activity in soybean raw material were developed. The use of indirect enzyme immunoassay for BBI detection during its isolation from different sources was demonstrated.

The refolding, purification, and activity analysis of a rice Bowman-Birk inhibitor expressed in Escherichia coli

A putative rice trypsin/chymotrypsin inhibitor of the Bowman-Birk family, RBBI-8 of about 20 kDa, was expressed in Escherichia coli as a fusion protein bearing an N-terminal (His)6 purification tag. The expressed recombinant protein, rRBBI-8, is insoluble and accumulates as inclusion bodies. The insoluble protein was solubilized in 8 M urea under reducing environment and then refolded into its active conformation under optimized redox conditions. Strategies used to optimize yield and efficiency include selecting the redox system, increasing protein concentration during refolding by adding the denatured protein in a stepwise way, utilizing additives to prevent aggregation, and selecting buffer-exchanging conditions. A Ni-chelate affinity column was then employed to purify the renatured protein. rRBBI-8 shows strong inhibitory activity against trypsin and it can slightly inhibit chymotrypsin. In this study, a refolding and purification system was set up for this cysteine-rich recombinant protein expressed in a prokaryotic system.

Purification and primary structure determination of a Bowman-Birk trypsin inhibitor from Torresea cearensis seeds

A Bowman-Birk-type trypsin inhibitor (TcTI) was purified from seeds of Torresea cearensis, a Brazilian native tree of the Papilionoideae sub-family of Leguminosae. Three forms of the inhibitor were separated by anion exchange chromatography. The major form with 63 amino acids was entirely sequenced; it shows a high structural similarity to the Bowman-Birk inhibitors from other Leguminosae. The putative reactive sites of the inhibitor are a lysine residue at position 15 and a histidine at position 42 as identified by alignment to related inhibitors, direct chemical modification and specific enzymatic degradation. Immunoprecipitation with antibodies raised in rats is reduced significantly if TcTI is complexed with chymotrypsin and, to a lesser degree, if complexed with trypsin. TcTI forms a ternary complex with trypsin and chymotrypsin. The binary complexes with trypsin or chymotrypsin were isolated by gel filtration. Dissociation constants of the complexes with trypsin, plasmin, chymotrypsin, and factor XIIa are 1, 36, 50, 1450 nM, respectively; human plasma kallikrein, human factor Xa, porcine pancreatic kallikrein and bovine thrombin are not inhibited. TcTI prolongs blood clotting time of the contact phase activation pathway by inhibition of FXIIa.

A rapid purification method for soybean Bowman-Birk protease inhibitor using hydrophobic-interaction chromatography

A protein fraction was isolated from defatted soybean flour by extraction at acid pH, 40% ammonium sulfate precipitation, hydrophobic interaction chromatography, and gel filtration chromatography. SDS-PAGE, under reducing conditions, confirmed it as a homogeneous preparation. This conclusion was consistent with N-terminal amino acid sequence data (20 cycles) which showed a major sequence identical to those reported for soybean Bowman-Birk-type protease inhibitor (BBI), and also indicated a minimum 95% purity based on recoveries of PTH-amino acid residues. The purified fraction inhibited both trypsin and chymotrypsin with average specific activities of 350 and 672 units mg(-1), respectively. Compared with classical BBI purification, this procedure is very rapid requiring only 72-96 h to achieve a yield of 37 mg purified BBI per 200 g starting material.

Amino acid sequence of a Bowman-Birk proteinase inhibitor from pea seeds

Trypsin inhibitors from winter pea seeds (c.v. Frilene) have been purified by ammonium sulfate precipitation, gel filtration, and anion and cation exchange chromatography and shown to consist of six protease inhibitors (PSTI I, II, III, IVa, IVb, and V). Their molecular weights were determined by electrospray mass spectrometry as 6916, 6807, 7676, 7944, 7848 and 7844 D, respectively, and the sequences of the first 20 N-terminal amino acid residues of these six inhibitors were found to be identical. The complete amino acid sequence of PSTI IVa was determined. This protein comprises a total of 72 residues and has 14 cysteines, all involved in disulfide bridges. Comparison of the sequence of PSTI IVa with those of other leguminous Bowman-Birk type inhibitors revealed that PSTI could be classified as a group III inhibitor, closely related to Vicia faba and Vicia angustifolia inhibitors.

[Natural proteinase inhibitors as a basis for creating new drugs]

Isolation of the proteinases inhibitors, available for medicinal purposes, was described, where the inhibitor of the Kunitz type was obtained from bovine pancreas and the inhibitor of the Bowman-Birk type from soybeans. Screening of the immobilization procedures was carried out, which enabled the authors to produce the polymeric conjugates of the proteinase inhibitors exhibiting the maximal rate of activity against pancreatic proteinases and granulocyte elastases. Pharmacokinetics of the proteinase inhibitors obtained was studied. High molecular derivatives of the inhibitors from the bovine pancreas circulated in rat blood in larger quantities and longer, their total clearance was 5 times than native inhibitor preparations. The preparations containing these inhibitors from bovine pancreas exhibited a high therapeutic efficiency in treatment of rats with hemorrhagic pancreatitis and acute liver failure in rabbits.

[High molecular weight soy isoinhibitors of the Bowman-Birk type. Isolation, characteristics, and kinetics of interaction with proteinases]

Multiple forms of Bowman-Birk soybean inhibitor have for the first time been isolated from commercial soya flour and purified to homogeneity. Amino acid compositions and isoelectric points of the inhibitors were determined. The isolated inhibitors are shown to be related to classic (M 8000 Da, 2-II) and high molecular mass glycine-rich (M 17 000 Da, 3-II, 5-II) Bowman-Birk inhibitors. The inhibitor (2-II) was found to have two reactive sites and bind trypsin at one centre and alpha-chymotrypsin, cathepsin G and human leukocyte elastase at the other. Rate constants of the complex formation (ka) and complex dissociation (kd) were determined by following the kinetics of approaching to the steady state in a system including the enzyme, the substrate and various concentrations of the inhibitor.

On a Bowman-Birk family proteinase inhibitor from Erythrina variegata seeds

A Bowman-Birk family proteinase inhibitor (EBI) was isolated from the seeds of Erythrina variegata. The protein was purified by ion-exchange column chromatography on DEAE-cellulose followed by gel filtration on Sephadex G-75. The stoichiometry with trypsin was estimated to be 1:1, while that with chymotrypsin was not obvious, as determined from the titration patterns of its inhibitory activities. The complete amino acid sequence of EBI was determined by sequencing tryptic and chymotryptic peptides. The EBI protein consists of 61 amino acid residues, which is the shortest among the Bowman-Birk family inhibitors sequenced to date, and has a M(r) of 6,689. Comparison of this sequence with those of other leguminous Bowman-Birk family inhibitors revealed that EBI could be classified as a group II inhibitor, showing the best homology (67%) to the Bowman-Birk proteinase inhibitor from soybeans.

Purification and characterization of three proteinase inhibitors from Canavalia lineata seeds

Three proteinase inhibitors (CLTI-I, -II and -III) were purified from the seeds of Canavalia lineata by DEAE-Toyopearl, hydroxyapatite, and anhydrotrypsin-Sepharose column chromatographies. All the inhibitors bound to trypsin at a 1:1 molar ratio and inhibited the enzyme with dissociation constants of 3-7 x 10(-9) M. They also showed the inhibitory activities on chymotrypsin. CTLI-I and -II had an identical M(r) of 8000 and very close isoelectric points (4.57 and 4.50), and existed mainly as trimers under physiological conditions. The high content of half-cystine residues and the high stability to pH and heat have suggested that these are Bowman-Birk type inhibitors. On the other hand, CLTI-III, with an M(r) of 20,500 was classified as a Kunitz (soybean) family inhibitor on the basis of the amino acid composition as well as the homology of its N-terminal 17 residues to other Kunitz inhibitors.

Crystallization and preliminary X-ray diffraction studies on a trypsin/chymotrypsin double-headed inhibitor from horse gram

The Bowman-Birk family of proteinase inhibitors from seeds of leguminous plants usually have a molecular mass of 8000 to 10,000 Da. Horse gram (Dolichos bifloros or Macrotyloma uniflorum) seeds contain an unusual Bowman-Birk inhibitor of molecular mass 15,500 Da active against both trypsin and chymotrypsin. In order to elucidate its three-dimensional structure, its evolutionary relationship with the more usual Bowman-Birk inhibitors and to study the structure-function properties, this inhibitor has been purified and crystallized. The purified protein crystallizes easily under a variety of conditions in different crystal forms. Crystals obtained by precipitating the protein (3 to 5 mg/ml in 50mM Tris.HCl (pH 8.0)) with 5% ammonium sulphate and 2 to 3% PEG 4000 appear to be suitable for structure determination by X-ray diffraction. The crystals belong to cubic space group P2(1)3 (a = 110.81 A) and diffract X-rays to beyond 3.0 A resolution.

[Inhibition of cathepsin G and elastase from human granulocytes by multiple forms of the Bowman-Birk type of soy inhibitor]

A classical soybean inhibitor (Bowman-Birk inhibitor, BBI 2-IV) and two high molecular weight glycine-enriched inhibitors of the same type (3-II and 4-II) have been isolated, purified to homogeneity and characterized. All of the BBI isoforms have been found to effectively inhibit cathepsin G and human granulocyte elastase. The constants for leucocyte cathepsin G inhibition by classical BBI 2-IV (Ki = 1.2 x 10(-9) M) and high molecular mass BBI 3-II (Ki = 8.0 x 10(-8) M) as well as for leucocyte elastase inhibition by high molecular mass BBI 3-II (Ki = 1.1 x 10(-7) M) have been determined.

Specificity and mode of action of the muscle-type protein-arginine deiminase

The primary and secondary specificities and mode of action of the muscle-type protein-arginine deiminase (PAD) were investigated using various derivatives of Arg and its homologues, as well as Arg-containing peptides by quantitative analyses of the reaction products on reverse-phase HPLC. The enzyme converted benzoyl-D-Arg-p-nitroanilide into its citrulline derivative at 18% of the rate of the L-isomer, while the D-Arg residues in peptides were not deiminated to a significant extent. This suggests that PAD does not have strict stereospecificity and it is dependent on the structure of the residues or groups on both sides of the target Arg residue. In contrast, the benzoyl-/-ethyl ester derivatives of homoarginine, alpha-amino-beta-guanidino-propionic acid, canavanine, and NG-methyl-Arg, exhibited poor PAD susceptibility, suggesting that the length and nature of the arm as exactly three CH2 groups, and the integrity of the guanidyl group are quite strict specificity determinants. The enzyme action on Arg residues in peptides depends greatly on their position in the sequence, and on the nature of the neighboring residues. For example, deimination of Arg residues situated at positions 1-3 from the NH2-terminus, except for those preceded by a carbobenzoxy- or benzoyl-group, were in most cases very slow, whereas those at the COOH-terminus were deiminated relatively faster. A single Arg residue sandwiched between two Pro residues was not deiminated at all, while a pair of Arg residues between two Pro were deiminated moderately. Consequently, PAD exhibited a variety of modes of action on more than one Arg residues in the peptides tested. The results suggest the applicability of PAD, albeit quite limited, for selective modification of certain Arg residues in peptides and proteins by appropriately controlling reaction time and several other parameters. The PAD's mode of action was compared with those of three Arg-bond cleaving proteases.

Identification of a soluble enzyme from C3H/10T1/2 cells which is inhibited by the Bowman-Birk proteinase inhibitor

The anticarcinogenic Bowman-Birk proteinase inhibitor (BBI) inhibits a 70-kDa serine proteinase in C3H/10T1/2 transformed fibroblasts. Two serine proteinases, the proline endopeptidase and a novel neutral proteolytic activity, both having a mass of approximately 70-kDa, were isolated from the cytoplasm of C3H/10T1/2 cells. BBI did not inhibit diisopropylfluorophosphate binding to the proline endopeptidase or its ability to hydrolyze peptides. However, BBI blocked the binding of diisopropylfluorophosphate and inhibited the cleavage of peptides by the novel cytoplasmic enzyme. Thus BBI does not inhibit the proline endopeptidase but another soluble 70-kDa serine proteinase from C3H/10T1/2 cells.

Purification, characterization, and amino acid sequence of foxtail millet trypsin inhibitor III

One of the major trypsin inhibitors of foxtail millet, Setaria italica, was purified from a seed extract to an electrophoretically homogeneous protein by methods including chromatofocusing and affinity chromatography. This inhibitor (FMTI-III) was shown to be specific and single-headed for trypsin. The molecular weight and the amino acid composition together with the above nature were identical with those of another major trypsin inhibitor (FMTI-II) previously purified from foxtail millet grain. Sequence analysis of FMTI-III indicated that the protein contains 67 amino acid residues, the sequence of which is the same as that of FMTI-II except for the replacement of the C-terminal glutamine by glutamic acid. This single amino acid substitution had no effect on inhibitor-enzyme association.

The Bowman-Birk inhibitor. Trypsin- and chymotrypsin-inhibitor from soybeans

Four decades of studies on the isolation, characterization, properties, structure, function and possible uses of the Bowman-Birk trypsin- and chymotrypsin-inhibitor from soybeans are reviewed. Starting from Bowman's Acetone Insoluble factor, designated Ai, AA and SBTIAA, the Bowman-Birk inhibitor (BBI) was found to be a protein molecule consisting of a chain of 71 amino acids cross linked by 7 disulfide bonds, with a tendency to self-associate. BBI possesses two independent sites of inhibition, one at Lys 16-Ser 17 against trypsin and the other at Leu 43-Ser 44 against chymotrypsin. It forms a 1:1 complex with either trypsin or chymotrypsin and a ternary complex with both enzymes. Ingestion of BBI by rats, chicks or quails affects the size and protein biosynthesis of the pancreas. Establishment of the full covalent structure of BBI revealed a high homology in the sequences around the two inhibitory sites, suggesting evolutionary gene duplication from a single-headed ancestral inhibitor. Scission of BBI by CNBr followed by pepsin results in two active fragments, one that inhibits trypsin and the other, chymotrypsin. Replacements and substitutions in the reactive sites result in changes in inhibitory activity and in specificity of inhibition. Conformation studies, labeling of BBI with a photoreactive reagent, chemical synthesis of cyclic peptides that include inhibitory sites, in vitro synthesis of BBI, and species specificity regarding the inhibited enzymes are described. The significance of BBI as a prototype of a family of inhibitors present in all legume seeds is discussed.

Studies on soybean trypsin inhibitors. X. Isolation and partial characterization of four soybean double-headed proteinase inhibitors

Four Bowman-Birk type double-headed inhibitors (B, C-II, D-II, and E-I) were isolated from soybeans. Inhibitor B was different from Bowman-Birk inhibitor only in chromatographic behavior. One mole of C-II inhibited one mole each of bovine trypsin and bovine alpha-chymotrypsin, probably at the same site, and porcine elastase at another reactive site. In the ordinary assay system D-II and E-I inhibited only trypsin activity at a non-stoichiometric inhibitor-enzyme ratio of 1:1.4, and the complexes had rather high dissociation constants. These inhibitors were all inactive toward subtilisin BPN'.