Decoding the Duality of Antinutrients: Assessing the Impact of Protein Extraction Methods on Plant-Based Protein Sources.

This review aims to provide an updated overview of the effects of protein extraction/recovery on antinutritional factors (ANFs) in plant protein ingredients, such as protein-rich fractions, protein concentrates, and isolates. ANFs mainly include lectins, trypsin inhibitors, phytic acid, phenolic compounds, oxalates, saponins, tannins, and cyanogenic glycosides. The current technologies used to recover proteins (e.g., wet extraction, dry fractionation) and novel technologies (e.g., membrane processing) are included in this review. The mechanisms involved during protein extraction/recovery that may enhance or decrease the ANF content in plant protein ingredients are discussed. However, studies on the effects of protein extraction/recovery on specific ANFs are still scarce, especially for novel technologies such as ultrasound- and microwave-assisted extraction and membrane processing. Although the negative effects of ANFs on protein digestibility and the overall absorption of plant proteins and other nutrients are a health concern, it is also important to highlight the potential positive effects of ANFs. This is particularly relevant given the rise of novel protein ingredients in the market and the potential presence or absence of these factors and their effects on consumers' health.

Expression and Purification of Recombinant Bowman-Birk Trypsin Inhibitor from Foxtail Millet Bran and Its Anticolorectal Cancer Effect In Vitro and In Vivo.

Trypsin inhibitors derived from plants have various pharmacological activities and promising clinical applications. In our previous study, a Bowman-Birk-type major trypsin inhibitor from foxtail millet bran (FMB-BBTI) was extracted with antiatherosclerotic activity. Currently, we found that FMB-BBTI possesses a prominent anticolorectal cancer (anti-CRC) activity. Further, a recombinant FMB-BBTI (rFMB-BBTI) was successfully expressed in a soluble manner in host strain Escherichia coli. BL21 (DE3) was induced by isopropyl-ß-d-thiogalactoside (0.1 mM) at 37 °C for 3.5 h by the pET28a vector system. Fortunately, a purity greater than 93% of rFMB-BBTI with anti-CRC activity was purified by nickel-nitrilotriacetic acid affinity chromatography. Subsequently, we found that rFMB-BBTI displays a strikingly anti-CRC effect, characterized by the inhibition of cell proliferation and clone formation ability, cell cycle arrest at the G2/M phase, and induction of cell apoptosis. It is interesting that the rFMB-BBTI treatment had no obvious effect on normal colorectal cells in the same concentration range. Importantly, the anti-CRC activity of rFMB-BBTI was further confirmed in the xenografted nude mice model. Taken together, our study highlights the anti-CRC activity of rFMB-BBTI in vitro and in vivo, uncovering the clinical potential of rFMB-BBTI as a targeted agent for CRC in the future.

A Novel Trypsin Kunitz-Type Inhibitor from Cajanus cajan Leaves and Its Inhibitory Activity on New Cancer Serine Proteases and Its Effect on Tumor Cell Growth.

A novel trypsin inhibitor from Cajanus cajan (TIC) fresh leaves was partially purified by affinity chromatography. SDS-PAGE revealed one band with about 15 kDa with expressive trypsin inhibitor activity by zymography. TIC showed high affinity for trypsin (Ki = 1.617 µM) and was a competitive inhibitor for this serine protease. TIC activity was maintained after 24 h of treatment at 70 °C, after 1 h treatments with different pH values, and ß-mercaptoethanol increasing concentrations, and demonstrated expressive structural stability. However, the activity of TIC was affected in the presence of oxidizing agents. In order to study the effect of TIC on secreted serine proteases, as well as on the cell culture growth curve, SK-MEL-28 metastatic human melanoma cell line and CaCo-2 colon adenocarcinoma was grown in supplemented DMEM, and the extracellular fractions were submitted salting out and affinity chromatography to obtain new secreted serine proteases. TIC inhibited almost completely, 96 to 89%, the activity of these serine proteases and reduced the melanoma and colon adenocarcinoma cells growth of 48 and 77% respectively. Besides, it is the first time that a trypsin inhibitor was isolated and characterized from C. cajan leaves and cancer serine proteases were isolated and partial characterized from SK-MEL-28 and CaCo-2 cancer cell lines. Furthermore, TIC shown to be potent inhibitor of tumor protease affecting cell growth, and can be one potential drug candidate to be employed in chemotherapy of melanoma and colon adenocarcinoma.

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 ß-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.

A new Kunitz trypsin inhibitor from Erythrina poeppigiana exhibits antimicrobial and antibiofilm properties against bacteria.

Erythrina poeppigiana belongs to Fabaceae family (subfamily Papillionoideae) and is commonly found in tropical and subtropical regions in Brazil. Herein, we described the purification and characterization of a new Kunitz-type inhibitor, obtained from E. poeppigiana seeds (EpTI). EpTI is composed by three isoforms of identical amino-terminal sequences with a molecular weight ranging from 17 to 20 kDa. The physicochemical features showed by EpTI are common to Kunitz inhibitors, including the dissociation constant (13.1 nM), stability against thermal (37-100 °C) and pH (2-10) ranging, and the presence of disulfide bonds stabilizing its reactive site. Furthermore, we investigated the antimicrobial, anti-adhesion, and anti-biofilm properties of EpTI against Gram-positive and negative bacteria. The inhibitor showed antimicrobial activity with a minimum inhibitory concentration (MIC, 5-10 µM) and minimum bactericidal concentration (MBC) of 10 µM for Enterobacter aerogenes, Enterobacter cloacae, Klebsiella pneumoniae, Staphylococcus aureus, and Staphylococcus haemolyticus. The combination of EpTI with ciprofloxacin showed a marked synergistic effect, reducing the antibiotic concentration by 150%. The increase in crystal violet uptake for S. aureus and K. pneumoniae strains was approximately 30% and 50%, respectively, suggesting that the bacteria plasma membrane is targeted by EpTI. Treatment with EpTI at 1x and 10 x MIC significantly reduced the biofilm formation and prompted the disruption of a mature biofilm. At MIC/2, EpTI decreased the bacterial adhesion to polystyrene surface within 2 h. Finally, EpTI showed low toxicity in animal model Galleria mellonella. Given its antimicrobial and anti-biofilm properties, the EpTI sequence might be used to design novel drug prototypes.

Potent Inhibitor of Human Trypsins from the Aeruginosin Family of Natural Products.

Serine proteases regulate many physiological processes and play a key role in a variety of cancers. Aeruginosins are a family of natural products produced by cyanobacteria that exhibit pronounced structural diversity and potent serine protease inhibition. Here, we sequenced the complete genome of Nodularia sphaerocarpa UHCC 0038 and identified the 43.7 kb suomilide biosynthetic gene cluster. Bioinformatic analysis demonstrated that suomilide belongs to the aeruginosin family of natural products. We identified 103 complete aeruginosin biosynthetic gene clusters from 12 cyanobacterial genera and showed that they encode an unexpected chemical diversity. Surprisingly, purified suomilide inhibited human trypsin-2 and -3, with IC50 values of 4.7 and 11.5 nM, respectively, while trypsin-1 was inhibited with an IC50 of 104 nM. Molecular dynamics simulations suggested that suomilide has a long residence time when bound to trypsins. This was confirmed experimentally for trypsin-1 and -3 (residence times of 1.5 and 57 min, respectively). Suomilide also inhibited the invasion of aggressive and metastatic PC-3M prostate cancer cells without affecting cell proliferation. The potent inhibition of trypsin-3, together with a long residence time and the ability to inhibit prostate cancer cell invasion, makes suomilide an attractive drug lead for targeting cancers that overexpress trypsin-3. These results substantially broaden the genetic and chemical diversity of the aeruginosin family and suggest that aeruginosins may be a source of selective inhibitors of human serine proteases.

Chemical Composition and in vitro Anti-inflammatory Activity of Wheat Germ Oil Depending on the Extraction Procedure.

This study aimed to examine the chemical composition of wheat germ oil extracted by three different methods, and to evaluate its inhibitory effect on the cyclooxygenase and proteinase activities. The results showed that the contents of policosanols, tocopherols and phytosterols were affected by the extraction procedure. However, the fatty acid composition of the different oil extracts was nearly the same. Among the tested oils samples, cold pressed oil exhibited the strongest inhibitory activity against proteinase (93.4%, IC50 =195.7 µg/mL) and cyclooxygenase 1 (80.5%, IC50 =58.6 µg/mL). Furthermore, the cold pressed oil had the highest content of octacosanol, ß-sitosterol and α-linolenic acid, suggesting that those bioactive compounds could be essential for the potent ani-cyclooxygenase activity. The present data revealed that wheat germ oil contained cyclooxygenase and trypsin inhibitors, which are the promising therapeutic target for the treatment of various inflammatory diseases. Thus, wheat germ oil might be used to develop functional foods and pharmaceutic products for the human health.

Identification of sustainable trypsin active-site inhibitors from Nigrospora sphaerica strain AVA-1.

Trypsin is a protein-digesting enzyme that is essential for the growth and regeneration of bone, muscle, cartilage, skin, and blood. The trypsin inhibitors have various role in diseases such as inflammation, Alzheimer's disease, pancreatitis, rheumatoid arthritis, cancer prognosis, metastasis and so forth. From 10 endophytic fungi isolated, we were able to screen only one strain with the required activity. The fungus with activity was obtained as an endophyte from Dendrophthoe falcata and was later identified as Nigrospora sphaerica. The activity was checked by enzyme assays using trypsin. The fungus was fermented and the metabolites were extracted and further purified by bioassay-guided chromatographic methods and the compound isolated was identified using gas chromatography-mass spectrometry. The compound was identified as quercetin. Docking studies were employed to study the interaction. The absorption, distribution, metabolism, and excretion analysis showed satisfactory results and the compound has no AMES and hepatotoxicity. This study reveals the ability of N. sphaerica to produce bioactive compound quercetin has been identified as a potential candidate for trypsin inhibition. The present communication describes the first report claiming that N. sphaerica strain AVA-1 can produce quercetin and it can be considered as a sustainable source of trypsin active-site inhibitors.

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.

Structural insights and molecular dynamics into the inhibitory mechanism of a Kunitz-type trypsin inhibitor from Tamarindus indica L.

Trypsin inhibitors from tamarind seed have been studied in vitro and in preclinical studies for the treatment of obesity, its complications and associated comorbidities. It is still necessary to fully understand the structure and behaviour of these molecules. We purifed this inhibitor, sequenced de novo by MALDI-TOF/TOF, performed its homology modelling, and assessed the interaction with the trypsin enzyme through molecular dynamics (MD) simulation under physiological conditions. We identified additional 75 amino acid residues, reaching approximately 72% of total coverage. The four best conformations of the best homology modelling were submitted to the MD. The conformation n°287 was selected considering the RMSD analysis and interaction energy (-301.0128 kcal.mol-1). Residues Ile (54), Pro (57), Arg (59), Arg (63), and Glu (78) of pTTI presented the highest interactions with trypsin, and arginine residues were mainly involved in its binding mechanism. The results favour bioprospecting of this protein for pharmaceutical health applications.

Identification and Target-Modification of SL-BBI: A Novel Bowman-Birk Type Trypsin Inhibitor from Sylvirana latouchii.

The peptides from the ranacyclin family share similar active disulphide loop with plant-derived Bowman-Birk type inhibitors, some of which have the dual activities of trypsin inhibition and antimicrobial. Herein, a novel Bowman-Birk type trypsin inhibitor of the ranacyclin family was identified from the skin secretion of broad-folded frog (Sylvirana latouchii) by molecular cloning method and named as SL-BBI. After chemical synthesis, it was proved to be a potent inhibitor of trypsin with a Ki value of 230.5 nM and showed weak antimicrobial activity against tested microorganisms. Modified analogue K-SL maintains the original inhibitory activity with a Ki value of 77.27 nM while enhancing the antimicrobial activity. After the substitution of active P1 site to phenylalanine and P2' site to isoleucine, F-SL regenerated its inhibitory activity on chymotrypsin with a Ki value of 309.3 nM and exhibited antiproliferative effects on PC-3, MCF-7 and a series of non-small cell lung cancer cell lines without cell membrane damage. The affinity of F-SL for the ß subunits in the yeast 20S proteasome showed by molecular docking simulations enriched the understanding of the possible action mode of Bowman-Birk type inhibitors. Further mechanistic studies have shown that F-SL can activate caspase 3/7 in H157 cells and induce apoptosis, which means it has the potential to become an anticancer agent.

Stability of trypsin inhibitor isolated from potato fruit juice against pH and heating treatment and in vitro gastrointestinal digestion.

Potato trypsin inhibitor (PTI) was obtained from imitated potato wastewater through a sustainable method of sequential acid precipitation, salting out, and ultrafiltration. PTI had a favorable inhibition with the low IC50 of 6.861 ± 0.107 mg/L. To explore stability of PTI against pH and heating treatment, PTI secondary structure was investigated by circular dichroism and inhibition was determined using the BAPNA method. The results indicated that PTI exerted a certain heat resistance and excellent stability over a wide pH range. Also, correlation analysis displayed ß-sheet and ß-turn contents of PTI had a positive correlation with inhibition, whereas α-helix and random coil contents were negatively correlated with inhibition. During in vitro digestion, the limited loss rate of activity (29.28%) and degree of hydrolysis (24.39%) suggested that PTI presented sufficient resistance to gastrointestinal digestion. These findings would extend beneficial hints to convert potato wastewater by-product into the potential anti-obesity ingredient in future.

Dual Insecticidal Effects of Adenanthera pavonina Kunitz-Type Inhibitor on Plodia interpunctella is Mediated by Digestive Enzymes Inhibition and Chitin-Binding Properties.

The Indianmeal moth, Plodia interpunctella, is one of the most damaging pests of stored products. We investigated the insecticidal properties of ApKTI, a Kunitz trypsin inhibitor from Adenanthera pavonina seeds, against P. interpunctella larvae through bioassays with artificial diet. ApKTI-fed larvae showed reduction of up to 88% on larval weight and 75% in survival. Trypsin enzymes extracted from P. interpunctella larvae were inhibited by ApKTI, which also demonstrated capacity to bind to chitin. Kinetic studies revealed a non-competitive inhibition mechanism of ApKTI for trypsin, which were further corroborated by molecular docking studies. Furthermore, we have demonstrated that ApKTI exhibits a hydrophobic pocket near the reactive site loop probably involved in chitin interactions. Taken together, these data suggested that the insecticidal activity of ApKTI for P. interpunctella larvae involves a dual and promiscuous mechanisms biding to two completely different targets. Both processes might impair the P. interpunctella larval digestive process, leading to larvae death before reaching the pupal stage. Further studies are encouraged using ApKTI as a biotechnological tool to control insect pests in field conditions.

A Versatile and Robust Serine Protease Inhibitor Scaffold from Actinia tenebrosa.

Serine proteases play pivotal roles in normal physiology and a spectrum of patho-physiological processes. Accordingly, there is considerable interest in the discovery and design of potent serine protease inhibitors for therapeutic applications. This led to concerted efforts to discover versatile and robust molecular scaffolds for inhibitor design. This investigation is a bioprospecting study that aims to isolate and identify protease inhibitors from the cnidarian Actinia tenebrosa. The study isolated two Kunitz-type protease inhibitors with very similar sequences but quite divergent inhibitory potencies when assayed against bovine trypsin, chymostrypsin, and a selection of human sequence-related peptidases. Homology modeling and molecular dynamics simulations of these inhibitors in complex with their targets were carried out and, collectively, these methodologies enabled the definition of a versatile scaffold for inhibitor design. Thermal denaturation studies showed that the inhibitors were remarkably robust. To gain a fine-grained map of the residues responsible for this stability, we conducted in silico alanine scanning and quantified individual residue contributions to the inhibitor's stability. Sequences of these inhibitors were then used to search for Kunitz homologs in an A. tenebrosa transcriptome library, resulting in the discovery of a further 14 related sequences. Consensus analysis of these variants identified a rich molecular diversity of Kunitz domains and expanded the palette of potential residue substitutions for rational inhibitor design using this domain.

A New Approach of Extraction of α-Amylase/trypsin Inhibitors from Wheat (Triticum aestivum L.), Based on Optimization Using Plackett-Burman and Box-Behnken Designs.

Wheat is one of the most consumed foods in the world and unfortunately causes allergic reactions which have important health effects. The α-amylase/trypsin inhibitors (ATIs) have been identified as potentially allergen components of wheat. Due to a lack of data on optimization of ATI extraction, a new wheat ATIs extraction approach combining solvent extraction and selective precipitation is proposed in this work. Two types of wheat cultivars (Triticum aestivum L.), Julius and Ponticus were used and parameters such as solvent type, extraction time, temperature, stirring speed, salt type, salt concentration, buffer pH and centrifugation speed were analyzed using the Plackett-Burman design. Salt concentration, extraction time and pH appeared to have significant effects on the recovery of ATIs (p < 0.01). In both wheat cultivars, Julius and Ponticus, ammonium sulfate substantially reduced protein concentration and inhibition of amylase activity (IAA) compared to sodium chloride. The optimal conditions with desirability levels of 0.94 and 0.91 according to the Doehlert design were: salt concentrations of 1.67 and 1.22 M, extraction times of 53 and 118 min, and pHs of 7.1 and 7.9 for Julius and Ponticus, respectively. The corresponding responses were: protein concentrations of 0.31 and 0.35 mg and IAAs of 91.6 and 83.3%. Electrophoresis and MALDI-TOF/MS analysis showed that the extracted ATIs masses were between 10 and 20 kDa. Based on the initial LC-MS/MS analysis, up to 10 individual ATIs were identified in the extracted proteins under the optimal conditions. The positive implication of the present study lies in the quick assessment of their content in different varieties especially while considering their allergenic potential.

LUTI: a double-function inhibitor isolated from naked flax seeds.

Acute glucose fluctuation during the postprandial period causes a risk for type 2 diabetes mellitus (T2DM). α-Glucosidase inhibitors have been approved as therapeutic agents for diabetes. In the present study, a protein with α-glucosidase inhibitory activity from Flax (Linum usitatissimum) seeds was isolated using a one-step purification with Q-Sepharose4B column, followed by Sephacryl S-200 size-exclusion chromatography. It was identified as a trypsin inhibitor, named L. usitatissimum trypsin inhibitor (LUTI). The half maximal inhibitory concentration (IC50) of LUTI was 113.92 µM for α-glucosidase and 6.17 µM for trypsin. Lineweaver-Burk kinetic experiment showed that the protein exhibited two distinct inhibitory modes, a competitive inhibitor type for α-glucosidase and a non-competitive type for trypsin. The interaction between LUTI and α-glucosidase was detected through gel filtration chromatography and dynamic light scattering. Increased glucose consumption and lactic acid production were also observed following LUTI treatment in Caco-2 and HepG2 cells. LUTI inhibits not only the activity of trypsin but also the activity of α-glucosidase. It is expected that LUTI will become an oral hypoglycemic polypeptide drug for T2DM.

Isolation and partial structural characterization of new Kunitz-type trypsin inhibitors from the pike cestode Triaenophorus nodulosus.

The inhibitors produced by the parasitic worms successfully protect them from the host's proteases and are supposed to underlie the host-parasite specificity. Our previous study has shown that the extracts from the pike tapeworm Triaenophorus nodulosus inhibit host proteinases and commercial trypsin. We aimed to isolate and identify the components responsible for trypsin inactivation. After a two-step separation the molecular masses were measured by SE-HPLC. The sample proved to contain four fractions represented by polypeptides (1-45 kDa) and low-molecular hydrophobic compounds. According to SDS-PAGE analysis, the major polypeptides in the fractions displaying the highest inhibition had masses of 14.4 kDa. The study culminated in partial N-terminal amino acid sequence analysis with a further search for homology. The research revealed two novel Kunitz-type proteins potentially responsible for the inhibitory capacity of the tapeworms against trypsin. Our findings extend the list of cestodes relying on Kunitz-type proteins in the host-parasite molecular cross-talk.

Purification of a trypsin inhibitor from Psoralea corylifolia seeds and its influence on developmental physiology of Bactrocera cucurbitae.

A trypsin inhibitor was purified from the seeds of Psoralea corylifolia by ion-exchange and affinity chromatography. The purified fractions were subjected to RP- HPLC which resolved into a single peak. SDS-PAGE analysis gave an apparent molecular weight of 18 kDa. P. corylifolia trypsin inhibitor (PCTI) was found to be a competitive inhibitor and was active over a broad temperature (10-100 °C) and pH (6-11) range. It was shown to have a deleterious effect on growth and development of larvae of the melon fruit fly, Bactrocera cucurbitae, when incorporated in artificial diet using various concentrations. The larval, pupal, total development period and larval mortality significantly increased during the treatment. Inhibitory effects were also observed on percentage emergence which was significantly reduced. Nutritional indices namely food assimilated (FA) and mean relative growth rate (MRGR) also decreased significantly with increase in concentration of PCTI. qRT-PCR results indicated that the expression of trypsin and chymotrypsin genes were down-regulated while elastase, catalase, GST, SOD and AP were up-regulated. PCTI was also effective against certain bacterial strains. These results indicated that the peptidase inhibitor from P. corylifolia may be a potential bio-control agent which can decrease the damage caused by B. cucurbitae and other related destructive pests.

Trypsin inhibitor from duck albumen: Purification and characterization.

Egg albumen is a potential source of trypsin inhibitor (TI), which has been widely used to improve textural property of surimi or surimi-based food products. TI from duck albumen was isolated and purified using ammonium sulfate precipitation at 20%-40% saturation and affinity chromatography using trypsin-CNBr-activated Sepharose 4B column. TI was purified with purity and yield of 111.8-fold and 0.6%, respectively. The purity of inhibitor was confirmed using Native-PAGE as indicated by the presence of single band. Molecular weight of purified TI was 43 kDa based on SDS-GAGE and gel filtration. The purified TI remained unchanged at temperatures below 60°C and the pH in the range of 7-9. The inhibitory activity of TI was decreased with the addition of salt higher than 5%. Inhibition kinetic study revealed that purified TI from duck albumen was uncompetitive inhibitor and the inhibition constant (Ki) was 508 nM. TI from duck egg albumen could serve as a food grade inhibitor for controlling undesirable proteolysis. PRACTICAL APPLICATIONS: Duck egg albumen has been known to be rich in protease inhibitors, which can be used as a protein additive to enhance gelling properties of surimi or surimi-based products. Therefore, it is of interest to isolate and purify TI from duck egg albumen. Information regarding characteristics of TI from duck albumen could be beneficial for further applications, in which duck albumen is better exploited.

A Novel Kunitzin-Like Trypsin Inhibitor Isolated from Defensive Skin Secretion of Odorrana versabilis.

Protease inhibitors that were identified from amphibian skin secretions with low molecular weights and potent inhibitory activity were thought to be potential candidates for novel peptide drugs. Here, a novel peptide with trypsin inhibitory activity was found in the skin secretion of the Chinese bamboo leaf odorous frog, Odorrana versabilis. Based on the sequence alignments of sequencing results, the novel peptide (ALKYPFRCKAAFC) was named as Kunitzin-OV. The synthetic replicate of Kunitzin-OV was subjected to a series of functional assays, and it exhibited a trypsin inhibitory activity with a Ki value of 3.042 µM, whereas, when Lys-9 at P1 position was substituted by Phe, trypsin inhibitory activity was undetected and the chymotrypsin inhibitory activity was optimized with a Ki value of 2.874 µM. However, its protease-binding loop was catabolized by trypsin during the trypsin cleavage test. In conclusion, Kunizin-OV is a novel peptide with trypsin inhibitory activity as a member of kunitzins, which is a non-typical Kunitz-like trypsin inhibitor with a highly conserved reactive site (K-A) and quite a short sequence.