Sequence analysis and molecular docking of antithrombotic peptides from casein hydrolysate by trypsin digestion

Emerging production techniques and potential health promoting properties of plant and animal protein-derived bioactive peptides

Bioactive peptides (BPs) are short amino acid sequences that that are known to exhibit physiological characteristics such as antioxidant, antimicrobial, antihypertensive and antidiabetic properties, suggesting that they could be exploited as functional foods in the nutraceutical industry. These BPs can be derived from a variety of food sources, including milk, meat, marine, and plant proteins. In the past decade, various methods including in silico, in vitro, and in vivo techniques have been explored to unravel underlying mechanisms of BPs. To forecast interactions between peptides and their targets, in silico methods such as BIOPEP, molecular docking and Quantitative Structure-Activity Relationship modeling have been employed. Additionally, in vitro research has examined how BPs affect enzyme activities, protein expressions, and cell cultures. In vivo studies on the contrary have appraised the impact of BPs on animal models and human subjects. Hence, in the light of recent literature, this review examines the multifaceted aspects of BPs production from milk, meat, marine, and plant proteins and their potential bioactivities. We envisage that the various concepts discussed will contribute to a better understanding of the food derived BP production, which could pave a way for their potential applications in the nutraceutical industry.

Characterization and Hydrolysis Mechanism Analysis of a Cold-Adapted Trypsin-Like Protease from Antarctic Krill

Cold-adapted proteases are capable of efficient protein hydrolysis at reduced temperatures, which offer significant potential applications in the area of low temperature food processing. In this paper, we attempted to characterize cold-adapted proteases from Antarctic krill. Antarctic krill possesses an extremely active autolytic enzyme system in their bodies, and the production of peptides and free amino acids accompanies the rapid breakdown of muscle proteins following the death. The crucial role of trypsin in this process is recognized. A cold-adapted trypsin named OUC-Pp-20 from Antarctic krill genome was cloned and expressed in Pichia pastoris. Recombinant trypsin is a monomeric protein of 26.8 ± 1.0 kDa with optimum reaction temperature at 25 °C. In addition, the catalytic specificity of OUC-Pp-20 was assessed by identifying its hydrolysis sites through LC-MS/MS. OUC-Pp-20 appeared to prefer Gln and Asn at the P1 position, which is an amino acid with an amide group in its side chain. Hydrolysis reactions on milk and shrimp meat revealed that it can effectively degrade allergenic components in milk and arginine kinase in shrimp meat. These findings update the current knowledge of cold-adapted trypsin and demonstrate the potential application of OUC-Pp-20 in low temperature food processing.

Fermented milks with specific Lactobacillus spp. with potential cardioprotective effects

In vitro and in vivo studies have reported the potential cardioprotective effects of fermented milks (FM). The aim of the present study was to evaluate the inhibitory activities of angiotensin converting enzyme (ACE), thrombin enzyme (TI) and micellar solubility of cholesterol of FM after 24 and 48 h of fermentation with Limosilactobacillus fermentum (J20, J23, J28 and J38), Lactiplantibacillus plantarum (J25) or Lactiplantibacillus pentosus (J34 and J37) exposed to simulated gastrointestinal digestion. Results showed that FM with J20 and J23 at 48 h of fermentation presented significantly (p < 0.05) higher degree of hydrolysis than other FM, and were not significantly different (p > 0.05) between them. Conversely, peptide relative abundance was significantly (p < 0.05) higher in FM with J20 than FM with J23. Moreover, IC₅₀ (protein concentration necessary to inhibit enzyme activity by 50%) for ACE inhibition were 0.33 and 0.5 mg/mL for FM with J20 and J23, respectively. For TI inhibition, the IC₅₀ were 0.3 and 0.24 mg/mL for FM with J20 and J23, respectively. Results exhibited 51 and 74% inhibition of micellar solubility cholesterol for FM with J20 and J23, respectively. Therefore, these results showed that not only peptide abundance, but also specific peptides might be responsible for these potential cardioprotective effects.

Identification and Anti-Hyperuricemic Activity of Xanthine Oxidase Inhibitory Peptides from Pacific White Shrimp and Swimming Crab Based on Molecular Docking Screening

The xanthine oxidase (XO) inhibitory peptides from pacific white shrimp or swimming crab were identified by molecular docking, and the anti-hyperuricemic activity of the peptides was confirmed in hyperuricemic cells. In our study, 17 novel XO inhibitory peptides were purified from pacific white shrimp or swimming crab, and Ala-Glu-Ala-Gln-Met-Trp-Arg (AEAQMWR, 891.01 Da, IC₅₀ = 8.85 ± 0.05 mM) exhibited the greatest XO inhibitory activity in vitro. Molecular docking results indicated that attractive charge, salt bridge, and hydrogen bond showed a crucial effect on the interactions of XO inhibitory peptides with the pivotal residues of Arg880, Glu802, and Glu1261. In addition, XO inhibitory peptides alleviated hyperuricemia by inhibiting inflammation and preventing increased uric acid transporter expression levels in hyperuricemia cells. Overall, these results further confirmed that screening of XO inhibitory peptides rapidly via molecular docking was feasible.

Peptides Isolated from Amphibian Skin Secretions with Emphasis on Antimicrobial Peptides

The skin of amphibians is a tissue with biological functions, such as defense, respiration, and excretion. In recent years, researchers have discovered a large number of peptides in the skin secretions of amphibians, including antimicrobial peptides, antioxidant peptides, bradykinins, insulin-releasing peptides, and other peptides. This review focuses on the origin, primary structure, secondary structure, length, and functions of peptides secreted from amphibians' skin. We hope that this review will provide further information and promote the further study of amphibian skin secretions, in order to provide reference for expanding the research and application of amphibian bioactive peptides.

Bioactive Peptides: An Understanding from Current Screening Methodology

Bioactive peptides with high potency against numerous human disorders have been regarded as a promising therapy in disease control. These peptides could be released from various dietary protein sources through hydrolysis processing using physical conditions, chemical agents, microbial fermentation, or enzymatic digestions. Considering the diversity of the original proteins and the complexity of the multiple structural peptides that existed in the hydrolysis mixture, the screening of bioactive peptides will be a challenge task. Well-organized and well-designed methods are necessarily required to enhance the efficiency of studying the potential peptides. This article, hence, provides an overview of bioactive peptides with an emphasis on the current strategy used for screening and characterization methods. Moreover, the understanding of the biological activities of peptides, mechanism inhibitions, and the interaction of the complex of peptide–enzyme is commonly evaluated using specific in vitro assays and molecular docking analysis.

Exploration of bioactive peptides from various origin as promising nutraceutical treasures: In vitro, in silico and in vivo studies

The current health scenarios describe growing public health problems, such as diabetes, hypertension and cancer. Therefore, researchers focused on studying these health issues are interested in exploring bioactive compounds from different food sources. Among them, bioactive peptides have garnered huge scientific interest because of their multifunctional biological activities such as antioxidative, antimicrobial, antihypertensive, anticancer, antidiabetic, immunomodulatory effect. They can be used as food and pharmaceutical ingredients with a great potential against disease targets. This review covers methods of production in general for several peptides obtained from various food sources including seed, milk and meat, and described their biological activities. Particular focus was given to bioinformatic tools to advance quantification, detection and characterize each peptide sequence obtained from different protein sources with predicted biological activity. Besides, various in vivo studies have been discussed to provide a better understanding of their physiological functions, which altogether could provide valuable information for their commercialization in future foods.

Development of peptide vaccine candidate using highly antigenic PE-PGRS family proteins to stimulate the host immune response against Mycobacterium tuberculosis H37Rv: an immuno-informatics approach

Tuberculosis (TB) is a fast spreading; transmissible disease caused by the Mycobacterium tuberculosis (M. tuberculosis). M. tuberculosis has a high death rate in its endemic regions due to a lack of appropriate treatment and preventative measures. We have used a vaccinomics strategy to create an effective multi-epitope vaccine against M. tuberculosis. The antigenic proteins with the highest antigenicity were utilised to predict cytotoxic T-lymphocyte (CTL), helper T-lymphocyte (HTL), and linear B-lymphocyte (LBL) epitopes. CTL and HTL epitopes were covered in 99.97% of the population. Seven epitopes each of CTL, HTL, and LBL were ultimately selected and utilised to develop a multi-epitope vaccine. A vaccine design was developed by combining these epitopes with suitable linkers and LprG adjuvant. The vaccine chimera was revealed to be highly immunogenic, non-allergenic, and non-toxic. To ensure a better expression within the Escherichia coli K12 (E. coli K12) host system, codon adaptation and in silico cloning were accomplished. Following that, various validation studies were conducted, including molecular docking, molecular dynamics simulation, and immunological simulation, all of which indicated that the designed vaccine would be stable in the biological environment and effective against M. tuberculosis infection. The immune simulation revealed higher levels of T-cell and B-cell activity, which corresponded to the actual immune response. Exposure simulations were repeated several times, resulting in increased clonal selection and faster antigen clearance. These results suggest that, if proposed vaccine chimera would test both in-vitro and in-vivo, it could be a viable treatment and preventive strategy for TB.Communicated by Ramaswamy H. Sarma.

Integration of Molecular Docking Analysis and Molecular Dynamics Simulations for Studying Food Proteins and Bioactive Peptides

In silico tools, such as molecular docking, are widely applied to study interactions and binding affinity of biological activity of proteins and peptides. However, restricted sampling of both ligand and receptor conformations and use of approximated scoring functions can produce results that do not correlate with actual experimental binding affinities. Molecular dynamics simulations (MDS) can provide valuable information in deciphering functional mechanisms of proteins/peptides and other biomolecules, overcoming the rigid sampling limitations in docking analysis. This review will discuss the information related to the traditional use of in silico models, such as molecular docking, and its application for studying food proteins and bioactive peptides, followed by an in-depth introduction to the theory of MDS and description of why these molecular simulation techniques are important in the theoretical prediction of structural and functional dynamics of food proteins and bioactive peptides. Applications, limitations, and future prospects of MDS will also be discussed.

Bioinformatics and Computer Simulation approaches to the discovery and analysis of Bioactive Peptides

The traditional process of separating and purifying bioactive peptides is laborious and time-consuming. Using a traditional process to identify is difficult, and there is a lack of fast and accurate activity evaluation methods. How to extract bioactive peptides quickly and efficiently is still the focus of bioactive peptides research. In order to improve the present situation of the research, bioinformatics techniques and peptidome methods are widely used in this field. At the same time, bioactive peptides have their own specific pharmacokinetic characteristics, so computer simulation methods have incomparable advantages in studying the pharmacokinetics and pharmacokinetic-pharmacodynamic correlation models of bioactive peptides. The purpose of this review is to summarize the combined applications of bioinformatics and computer simulation methods in the study of bioactive peptides, with focuses on the role of bioinformatics in simulating the selection of enzymatic hydrolysis and precursor proteins, activity prediction, molecular docking, physicochemical properties, and molecular dynamics. Our review shows that new bioactive peptide molecular sequences with high activity can be obtained by computer-aided design. The significance of the pharmacokinetic-pharmacodynamic correlation model in the study of bioactive peptides is emphasized. Finally, some problems and future development potential of bioactive peptides binding new technologies are prospected.

PM1-loaded recombinant human H-ferritin nanocages: A novel pH-responsive sensing platform for the identification of cancer cells

The aggregation-induced emission (AIE) material has been widely used in biological detection due to their unique property of fluorescing in aggregation state. However, the poor dispersion and biocompatibility limit its application in in vivo real-time imaging. Here, a novel strategy is designed to obtain pH-responsive AIE nanomaterials, working through 4-Undecoxy Tetraphenyl Ethylene Methacrylate (PM1) block, with excellent features (dispersion, biocompatibility, self-reconstruction and cancer specific recognition). The recombinant human H-ferritin (rHuHF) was used to prepare rHuHF-PM1 nanocomposites which effectively supported the dispersion and transfer of PM1 in the biological environment, even making it target tumor cells due to the overexpression of ferritin receptors on tumor cells. To simulate the changes of rHuHF in intracellular lysosomes, particle size and fluorescence of rHuHF-PM1 were analyzed, which reflected the loose structural changes of rHuHF nanocages in weak acid system that facilitated the degradation of macromolecular rHuHF in intracellular lysosomes and following release of PM1. The released PM1 molecules aggregated and emitted brilliant blue fluorescence. Several cell lines, Hela, HT-29, HepG2, L-O2 and HUVEC have all been sensitively detected and distinguished. Accordingly, this nanocage has a potential to be applied to disease diagnosis and provides a novel sensing platform for the identification of cancer.

Characterization of β-Sitosterol for Potential Selective GR Modulation

BACKGROUND

Although glucocorticoids (GCs) are characterized as powerful agents to treat inflammatory afflictions, they are accompanied by metabolic side effects which limit their usage. β-Sitosterol, as a minor component found in extraction of vegetable oil, was reported to have anti-inflammatory effects in RAW 264.7 cells.

OBJECTIVE

To test whether β-sitosterol has an effect to dissociate transrepression from transactivation as a selective novel GR binder, this work evaluated the dissociated characteristics of β-sitosterol.

METHODS

The probable binding interaction between β-sitosterol and GR was explored by molecular docking. The GR transcriptional activity of β-sitosterol was assessed in the reporter gene assay. The ability of β-sitosterol to modulate the transactivation and transrepression of GR was evaluated by real-time quantitative PCR analysis.

RESULTS AND DISCUSSION

In the present study, β-sitosterol treatment cannot induce GR-mediated transactivation. β-Sitosterol exerted a potential to inhibited the expression of GR target transrepressed gene without activating the expression of GR transactivation dependent gene. Molecular docking demonstrated that β-Sitosterol was able to bind the ligand binding domain of GR but unable to induce GR activation.

CONCLUSION

This work offers evidence that β-sitosterol may serve as a selective GR modulator.

Techniques, perspectives, and challenges of bioactive peptide generation: A comprehensive systematic review

Due to the digestible refractory and absorbable structures of bioactive peptides (BPs), they could induce notable biological impacts on the living organism. In this regard, the current study was devoted to providing an overview regarding the available methods for BPs generation by the aid of a systematic review conducted on the published articles up to April 2019. In this context, the PubMed and Scopus databases were screened to retrieve the related publications. According to the results, although the characterization of BPs mainly has been performed using enzymatic and microbial in-vitro methods, they cannot be considered as suitable techniques for further stimulation of digestion in the gastrointestinal tract. Therefore, new approaches for both in-vivo and in-silico methods for BPs identification should be developed to overcome the obstacles that belonged to the current methods. The purpose of this review was to compile the recent analytical methods applied for studying various aspects of food-derived biopeptides, and emphasizing generation at in vitro, in vivo, and in silico.

Bioactive peptides from food fermentation: A comprehensive review of their sources, bioactivities, applications, and future development

Bioactive peptides (BPs) are specific protein fragments that exert various beneficial effects on human bodies and ultimately influence health, depending on their structural properties and amino acid composition and sequences. By offering promising solutions to solve diverse health issues, the production, characterization, and applications of food-derived BPs have drawn great interest in the current literature and are of particular interest to the food and pharmaceutical industries. The microbial fermentation of protein from various sources is indubitably a novel way to produce BPs with numerous beneficial health effects. Apart from its lower cost as compared to enzymes, the BPs produced from microbial fermentation can be purified without further hydrolysis. Despite these features, current literature shows dearth of information on the BPs produced from food via microbial fermentation. Hence, there is a strong necessity to explore the BPs obtained from food fermentation for the development of commercial nutraceuticals and functional foods. As such, this review focuses on the production of BPs from different food sources, including the extensively studied milk and milk products, with emphasis on microbial fermentation. The structure-activity (antihypertensive, antioxidant, antimicrobial, opiate-like, anti-inflammatory, anticancer/antiproliferative, antithrombotic, hypolipidemic, hypocholesterolemic, and mineral binding) relationship, potential applications, future development, and challenges of BPs obtained from food fermentation are also discussed.

The structure and properties of MFG-E8 and the In vitro assessment of its toxic effects on myoblast cells

Four high-molecular-weight protein fractions of milk fat globule membrane (MFGM) were isolated from bovine milk. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), MALDI-TOF/TOF™ and Liquid chromatography electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) were used to measure the molecular sizes of the MFGM. Fourier transform infrared spectroscopy (FT-IR) and circular dichroism (CD) were performed to determine the conformations of the MFGM. The results showed that the main protein (98.33%) in MFGM protein fraction 2 was Milk fat globule epidermal growth factor-VIII (MFG-E8), with a molecular weight of 47.82 kDa. The secondary structural component measurements showed that the MFG-E8 consisted of 5% helix, 70% sheet and 25% random coil, and the results matched well with the prediction by SSPro 5.1 bioinformatic analysis. The thermograms analysis revealed that Td and△H of MFG-E8 were 60.50°Cand 132.29 kJ/mol. The in vitro digestibility of MFG-E8 showed that it can be enzymatically hydrolyzed in the stomach and relatively stable in the intestinal fluid. The in vitro C₂C₁₂ and Caco2 cell activity tests indicated that MFG-E8 promoted the proliferation of C₂C₁₂ myoblast cells without cytotoxicity. The biological functional properties of MFG-E8 may be related to the fact that MFG-E8 possesses a high level of β-sheet structure. Our results suggested that MFG-E8 possesses broad prospects not only for use in functional food products but also as a source of natural anti-sarcopenia drugs.

Heat treatments of peptides from oyster (Crassostrea gigas) and the impact on their digestibility and angiotensin I converting enzyme inhibitory activity

The changes of protein digestibility, the peptides in the digestive juice and angiotensin I converting enzyme (ACE) inhibitory activity after heating of oysters were investigated. The digestibility of raw oysters was 71.1%, and that of oysters heated at 100 °C was 67.9%. A total of 169 and 370 peptides were identified from the digestion of raw oysters and heated oysters, respectively. According to UPLC-Q-TOF-MS spectra, the peptides with a molecular weight below 2000 Da accounted for 87.6% of the total peptides of raw oysters and 94% of heated oysters. Testing the ACE inhibitory activity in vitro, the IC₅₀ values of raw oyster and cooked oyster were 6.77 μg/mL and 3.34 μg/mL, respectively. Taken together, the results showed that heated oysters could produce more active peptides and provide ACE inhibitory activity.

A novel thrombin inhibitory peptide discovered from leech using affinity chromatography combined with ultra-high performance liquid chromatography-high resolution mass spectroscopy

Thrombin (THR) inhibitors play an important role in the treatment of thrombotic diseases. This study established a THR-based bio-specific extraction coupled with affinity chromatography and ultra-high performance liquid chromatography-high resolution mass spectroscopy (UPLC-HR-MS) analysis method to screen and identify THR ligands in Leech. After evaluating the reliability of the screening method using positive control drug (hirudin), it was successfully used to screen the potential active constituents in leech. And a comprehensive analysis of the peptides in leech elution was performed by UPLC-HR-MS, a total of 34 peptides were identified. At the same time, anti-THR activity was explored and inferred by searching databases and published literature. As a result, six peptides were discovered to be potential active compounds in leech. Further, the six peptides were synthesized and in vitro enzymatic activity assay was performed. Finally, SYELPDGQVITIGNER was screened as an anti-THR peptide with an IC50 value of 255.75 µM and it was discovered for the first time from Whitmania pigra Whitman and Hirudo nipponica Whitman. The molecular docking study showed that THR inhibitory activity of the polypeptide was mainly attributed to the hydrogen bond interactions, van der Waals forces and electrostatic interactions interaction between polypeptide and THR. These results suggest that the polypeptide is a potential natural THR inhibitor that can be used as anticoagulant.

Identification of novel DPP-IV inhibitory peptides from Atlantic salmon (Salmo salar) skin

The aim of this study was to identify dipeptidyl peptidase IV (DPP-IV) inhibitory peptides from salmon skin collagen hydrolysate, and to evaluate the possible inhibition mechanism of DPP-IV and peptide. Salmon skin collagen was hydrolyzed by pepsin, trypsin, papain, or Alcalase 2.4 L, separately. Trypsin hydrolysate (10 mg/mL) showed the highest inhibitory activity of 66.12 ± 0.68%. The hydrolysate was separated into three fractions by ultrafiltration, and the inhibitory IC₅₀ of M1 (molecular weight <3 kDa) was 1.54 ± 0.06 mg/mL. M1 was separated by gel chromatography and RP-HPLC; A10 was the highest inhibitory fraction in the 12 fractions, i.e., IC₅₀ was 0.79 ± 0.13 mg/mL. A novel peptide LDKVFR with the IC₅₀ value of 0.1 ± 0.03 mg/mL (128.71 μM) was identified from A10. Molecular docking revealed that six hydrogen bonds and eight hydrophobic interactions between LDKVFR and DPP-IV were contributed to DPP-IV inhibition.

Whey-Derived Peptides Interactions with ACE by Molecular Docking as a Potential Predictive Tool of Natural ACE Inhibitors

Several milk/whey derived peptides possess high in vitro angiotensin I-converting enzyme (ACE) inhibitory activity. However, in some cases, poor correlation between the in vitro ACE inhibitory activity and the in vivo antihypertensive activity has been observed. The aim of this study is to gain insight into the structure-activity relationship of peptide sequences present in whey/milk protein hydrolysates with high ACE inhibitory activity, which could lead to a better understanding and prediction of their in vivo antihypertensive activity. The potential interactions between peptides produced from whey proteins, previously reported as high ACE inhibitors such as IPP, LIVTQ, IIAE, LVYPFP, and human ACE were assessed using a molecular docking approach. The results show that peptides IIAE, LIVTQ, and LVYPFP formed strong H bonds with the amino acids Gln 259, His 331, and Thr 358 in the active site of the human ACE. Interestingly, the same residues were found to form strong hydrogen bonds with the ACE inhibitory drug Sampatrilat. Furthermore, peptides IIAE and LVYPFP interacted with the amino acid residues Gln 259 and His 331, respectively, also in common with other ACE-inhibitory drugs such as Captopril, Lisinopril and Elanapril. Additionally, IIAE interacted with the amino acid residue Asp 140 in common with Lisinopril, and LIVTQ interacted with Ala 332 in common with both Lisinopril and Elanapril. The peptides produced naturally from whey by enzymatic hydrolysis interacted with residues of the human ACE in common with potent ACE-inhibitory drugs which suggests that these natural peptides may be potent ACE inhibitors.

Anticoagulant Decapeptide Interacts with Thrombin at the Active Site and Exosite-I

Thrombin can be used as a target for its inhibitors to prevent blood coagulation. A novel peptide (TKLTEEEKNR, PfCN) identified from αS2-casein (fragments 211-220) with high anticoagulant activity was screened and prepared. The activated partial thromboplastin time, prothrombin time, and thrombin time, at the concentration of 4 mM, prolonged about 19, 2.5 and 5.5 s, respectively. At the same concentration, the fibrinogen clotting time prolonged from 25.5 ± 0.7 to 38.3 ± 1.3 s. The thrombin inhibitory efficiency in vitro (IC₅₀ value of 29.27 mM) and antithrombosis effect in vivo were determined. The secondary structure of thrombin, which was influenced by PfCN, indicates that PfCN can bind to thrombin. Isothermal titration calorimetry and the chromogenic substrate test showed that PfCN belongs to the bivalent thrombin inhibitor like bivalirudin. Although the effect was not as good as bivalirudin, in the animal experiment, bleeding occurred in the bivalirudin group but not in the PfCN group. Moreover, molecular docking illustrates the mechanism for the antithrombin activity of PfCN. These results indicated that PfCN could be used as an effective thrombin inhibitor with broad potential for the prevention of thrombotic acute pulmonary embolism and other thrombotic events.

Identification and molecular docking study of fish roe-derived peptides as potent BACE 1, AChE, and BChE inhibitors

Acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and beta-secretase 1 (BACE 1) play vital roles in the development and progression of Alzheimer's disease (AD).

Biological and conventional food processing modifications on food proteins: Structure, functionality, and bioactivity

Food proteins are important nutrients for human health and thus make significant contributions to the unique functions of different foods. The modification of proteins through physical and biological processing could improve the functional and nutritional properties of food products; these changes can be attributed to modifications in particle size, solubility, emulsion stability, secondary structure, as well as the bioactivities of the proteins. Physical processing treatments might promote physical phenomena, such as combined friction, collision, shear forces, turbulence, and cavitation of particles, and lead to changes in the particle sizes of proteins. The objective of this review is to illustrate the effect of physical and biological processing on the structure, and physical and chemical properties of food-derived proteins and provide insights into the mechanism underlying structural changes. Many studies have suggested that physical and biological processes, such as ultrasound treatment, high pressure homogenization, ball mill treatment, and enzymatic hydrolysis could affect the structure, physical properties, and chemical properties of food-derived proteins. Some important applications of food-derived proteins are also discussed based on the relationships between their physical, chemical, and functional properties. Perspectives from fundamental or practical research are also brought in to provide a complete picture of the currently available relevant data.

Mechanism and inhibition kinetics of peptide P13 as thrombin inhibitor

Excessive coagulation can easily lead to arterial and venous thrombosis, which is the main reason for the evolution of myocardial infarction and cerebrovascular accidents. As a key coagulation factor for the coagulation pathway, thrombin has become a remarkable target for the control of thrombosis. The synthesized peptide P13 with amino acid sequence of N-RGDAGFAGDDAPR was expected to be an inhibitor with higher antithrombotic activity. The results showed that the IC₅₀ (50% inhibition of thrombin activity) of the peptide P13 was determined by colorimetric method to be 115 µM. And enzyme kinetic experiments showed that P13 was a competitive inhibitor of thrombin with K_i = 106 µM. Fluorescence spectra and three-dimensional fluorescence showed that P13 could alter the secondary structure of thrombin and the microenvironment of certain chromogenic amino acids. P13 can spontaneously bind with thrombin exosite 1 in the form of 1:1 mainly through hydrogen bonding and van der Waals force. And the optimal docking mode of P13 and thrombin was revealed by molecular docking with "-CDOCKER_Energy" of 178.679 kcal mol^-1. This study revealed P13 may become a potential anticoagulant drug widely used after further studies in preclinical and clinical trials.

In Vitro Antithrombotic and Hypocholesterolemic Activities of Milk Fermented with Specific Strains of Lactococcus lactis

Milk fermented with specific lactic acid bacteria (LAB) was reported to be a rich source of metabolites, such as peptides with different biological activities that may have a positive effect on cardiovascular health. Thus, in this study, the antithrombotic and hypocholesterolemic activities of fermented milk with specific strains of Lactococcus lactis were investigated before and after exposure to a simulated gastrointestinal digestion (SGD) model. The inhibition of thrombin-induced fibrin polymerization (IC₅₀ peptide concentration necessary to inhibit thrombin activity by 50%), anticoagulant activity, inhibition of micellar solubility of cholesterol and bile acid binding capacity of water soluble fractions (WSF) <3 kDa from fermented milk were evaluated. Results indicated that the WSF from fermented milk with Lc-572 showed antithrombotic (IC₅₀ = 0.049 mg/mL) and hypocholesterolemic (55% inhibition of micellar solubility of cholesterol and 27% bile acid binding capacity) activities. Meanwhile, fermented milk with Lc-571 showed mainly antithrombotic activity (IC₅₀ = 0.045 mg/mL). On the other hand, fermented milk with Lc-600 presented mainly hypocholesterolemic activity (31.4% inhibition of micellar solubility of and 70% bile acid binding capacity). Moreover, biological activities were not lost after simulated gastrointestinal digestion conditions. Thus, fermented milk with these specific L. lactis strains show potential for the development of functional foods.

Identification and molecular mechanism of antithrombotic peptides from oyster proteins released in simulated gastro-intestinal digestion

In this study, oyster (Crassostrea gigas) proteins were digested under in vitro gastrointestinal conditions to screen potential antithrombotic peptides. The sequences of the released peptides in the intestinal digestion phase were identified by ultra-performance liquid chromatography coupled to quadrupole time-of-flight MS (UPLC-Q-TOF-MS/MS). According to the antithrombotic activity analysis, the inhibitory ratio of oyster peptides showed an increasing trend, reaching up to 35.80% for a digestion period of 4 h. The APTT (activated partial thromboplastin time) and TT (thromboplastin time) were increased by oyster peptides for human serum in vitro. Oyster peptides showed a competitive inhibition effect on thrombin, based on Lineweaver-Burk plot analysis. Molecular docking between the antithrombotic peptides and thrombin (PDB: ) was conducted using Discovery Studio 2017. Potential inhibitors against thrombin and the mechanism of antithrombotic activity were predicted using the algorithm of CDOCKER. There are fourteen potential antithrombotic peptides, whose affinity with thrombin is higher than that of hirudin, as indicated by the "-CDOCKER energy" score (181.491). Peptide LSKEEIEEAKEV is similar in sequence to thrombin inhibitors. The binding sites of potential antithrombotic peptides against thrombin at the S1 pocket were compared with hirudin variant-2 (GDFEEIPEEYLQ). In addition, the peptides containing the RG/RGD sequence were identified, which can be hydrolyzed by thrombin as a substrate. Consequently, the oyster peptides released in simulated gastrointestinal digestion probably inhibit thrombin in two ways, not only as the inhibitor against the active site, but also as the substrate of thrombin. These results maybe be attributed to the potentially strong antithrombotic activity in the human digestive system.

Interaction of the synthetic antithrombotic peptide P10 with thrombin: a spectroscopy study

Thrombin is a critical serine protease in the coagulation system and is widely used as a target protein for antithrombotics. Spectroscopic analysis is a simple and effective method that is used to study the interaction between small molecules and proteins. In this study, the interactions of a potential antithrombotic peptide AGFAGDDAPR (P10) with thrombin were investigated by fluorescence spectroscopy, UV-vis spectroscopy, circular dichroism, Fourier-transform infrared spectroscopy and Raman spectroscopy, respectively. The results showed that the peptide P10 bonded to thrombin via hydrogen bonding and van der Waals forces, resulting in fluorescence quenching. And, the secondary structure of thrombin changed, the β-sheet decreased, and the random coil increased. The peptide P10 bonded to proline and lysine, and changed the space structure of thrombin, resulting in inhibition of thrombin activity. The results contributed to exploration of the mechanism of this potential antithrombotic drug interaction with thrombin in order to provide a preliminary understanding of the pharmacodynamic properties of P10.

In Silico Analysis of Bioactive Peptides in Invasive Sea Grass Halophila stipulacea

Halophila stipulacea is a well-known invasive marine sea grass in the Mediterranean Sea. Having been introduced into the Mediterranean Sea via the Suez Channel, it is considered a Lessepsian migrant. Although, unlike other invasive marine seaweeds, it has not demonstrated serious negative impacts on indigenous species, it does have remarkable invasive properties. The present in-silico study reveals the biotechnological features of H. stipulacea by showing bioactive peptides from its rubisc/o protein. These are features such as antioxidant and hypolipideamic activities, dipeptidyl peptidase-IV and angiotensin converting enzyme inhibitions. The reported data open up new applications for such bioactive peptides in the field of pharmacy, medicine and also the food industry.

Food-derived antithrombotic peptides: Preparation, identification, and interactions with thrombin

Thromboembolism and its sequelae have been the leading causes of morbidity and mortality throughout the world. Food-derived antithrombotic peptides, as potential ingredients in health-promoting functional foods targeting thrombus, have attracted increasing attention because of their high biological activities, low toxicity, and ease of metabolism in the human body. This review presents the conventional workflow of preparation, isolation and identification of antithrombotic peptides from various kinds of food materials. More importantly, to analyze the antithrombotic effects and mechanism of antithrombotic peptides, methods for interaction of anticoagulant peptides and thrombin, the main participant in thrombosis, were analyzed from biochemistry, solution chemistry and crystal chemistry. The present study is intended to highlight the recent advances in research of food-derived antithrombotic peptide as a novel vehicle in the field of food science and nutrition. Future outlooks are highlighted with the aim to suggest a research line to be followed in further studies with the introduced research approach.

An anticoagulant peptide from beta-casein: identification, structure and molecular mechanism

A bioactive peptide is identified from casein hydrolysates.

Identification and molecular docking study of novel angiotensin-converting enzyme inhibitory peptides from Salmo salar using in silico methods

BACKGROUND

In order to circumvent some challenges of the classical approach, the in silico method has been applied to the discovery of angiotensin-converting enzyme (ACE) inhibitory peptides from food proteins. In this study, some convenient and efficient in silico tools were utilized to identify novel ACE inhibitory peptides from Salmo salar.

RESULTS

Collagen from Salmo salar was digested in silico into hundreds of peptides. Results revealed that tetrapeptides PGAR and IGPR showed potent ACE inhibitory activity, with IC₅₀ values of 0.598 ± 0.12 and 0.43 ± 0.09 mmol L^-1 , respectively. The molecular docking result showed that PGAR and IGPR interact with ACE mostly via hydrogen bonds and attractive charge. Peptide IGPR interacts with Zn⁺ at the ACE active site, showing high inhibitory activity.

CONCLUSION

Interaction with Zn⁺ in ACE may lead to higher inhibitory activity of peptides, and Pi interactions may promote the effect of peptides on ACE. The in silico method can be an effective method to predict potent ACE inhibitory peptides from food proteins. © 2018 Society of Chemical Industry.

Identification and In Silico Prediction of Anticoagulant Peptides from the Enzymatic Hydrolysates of Mytilus edulis Proteins

Mytilus edulis is a typical marine bivalve mollusk. Many kinds of bioactive components with nutritional and pharmaceutical activities in Mytilus edulis were reported. In this study, eight different parts of Mytilus edulis tissues, i.e., the foot, byssus, pedal retractor muscle, mantle, gill, adductor muscle, viscera, and other parts, were separated and the proteins from these tissues were prepared. A total of 277 unique peptides from the hydrolysates of different proteins were identified by UPLC-Q-TOF-MS/MS, and the molecular weight distribution of the peptides in different tissues was investigated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The bioactivity of the peptides was predicted through the Peptide Ranker database and molecular docking. Moreover, the peptides from the adductor muscle were chosen to do the active validation of anticoagulant activity. The active mechanism of three peptides from the adductor muscle, VQQELEDAEERADSAEGSLQK, RMEADIAAMQSDLDDALNGQR, and AAFLLGVNSNDLLK, were analyzed by Discovery Studio 2017, which also explained the anticoagulant activity of the hydrolysates of proteins from adductor muscle. This study optimized a screening and identification method of bioactive peptides from enzymatic hydrolysates of different tissues in Mytilus edulis.

Anti-Alzheimers activity and molecular mechanism of albumin-derived peptides against AChE and BChE

Alzheimer's disease (AD) is a global health issue affecting millions of elderly people worldwide. The aim of the present study was to identify novel anti-AD peptides isolated from albumin. Anti-AD activities of the peptides were evaluated via inhibitory activities on acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Furthermore, the potential molecular mechanisms of the KLPGF/AChE were investigated by CDOCKER of Discovery studio 2017. The results revealed that peptide KLPGF could effectively inhibit AChE with an inhibition rate of 61.23% at a concentration of 50 μg mL^-1. In addition, the peptide KLPGF came in contact with acylation sites and peripheral anion sites of AChE. The present study demonstrates that the peptide KLPGF could become a potential functional food intervention in AD.

Identification of an ACE-Inhibitory Peptide from Walnut Protein and Its Evaluation of the Inhibitory Mechanism

In the present study, a novel angiotensin I-converting enzyme inhibitory (ACE inhibitory) peptide, EPNGLLLPQY, derived from walnut seed storage protein, fragment residues 80–89, was identified by ultra-high performance liquid chromatography electrospray ionization quadrupole time of flight mass spectrometry (UPLC-ESI-Q-TOF-MS/MS) from walnut protein hydrolysate. The IC₅₀ value of the peptide was 233.178 μM, which was determined by the high performance liquid chromatography method by measuring the amount of hippuric acid (HA) generated from the ACE decomposition substrate (hippuryl-l-histidyl-l-leucine (HHL) to assess the ACE activity. Enzyme inhibitory kinetics of the peptide against ACE were also conducted, by which the inhibitory mechanism of ACE-inhibitory peptide was confirmed. Moreover, molecular docking was simulated by Discovery Studio 2017 R2 software to provide the potential mechanisms underlying the ACE-inhibitory activity of EPNGLLLPQY.