Plant-derived Peptides Research Articles

Antioxidant Function and Application of Plant-Derived Peptides.

With the development of society and the improvement of people's health consciousness, the demand for antioxidants is increasing. As a natural antioxidant with no toxic side effects, antioxidant peptides are widely used in food, cosmetics, medicine, and other fields because of their strong antioxidant capacity and easy absorption by the human body. Plant-derived antioxidant peptides have attracted more attention than animal-derived antioxidant peptides because plants are more diverse than animals and produce a large number of protein-rich by-products during the processing of their products, which are the main source of antioxidant peptides. In this review, we summarize the source, structure and activity, other biological functions, mechanism of action, and comprehensive applications of plant antioxidant peptides, and look forward to their future development trends, which will provide a reference for further research and development of plant antioxidant peptides.

Plant-Derived Peptides: (Neglected) Natural Products for Drug Discovery

Plant-Derived Peptides: (Neglected) Natural Products for Drug Discovery

Isolation and Characterization of Insecticidal Cyclotides from Viola communis.

Cyclotides are cysteine-rich plant-derived peptides composed of 28-37 amino acids with a head-to-tail cyclic backbone and a knotted arrangement of three conserved disulfide bonds. Their beneficial biophysical properties make them promising molecules for pharmaceutical and agricultural applications. The Violaceae plant family is the major cyclotide-producing family, and to date, every examined plant from this family has been found to contain cyclotides. The presence of cyclotides in Viola communis was inferred by mass spectroscopy previously, but their sequences and properties had yet to be explored. In this study, the occurrence of cyclotides in this plant was investigated using proteomics and transcriptomics. Twenty cyclotides were identified at the peptide level, including two new members from the bracelet (Vcom1) and Möbius (Vcom2) subfamilies. Structural analysis of these newly identified peptides demonstrated a similar fold compared with cyclotides from the same respective subfamilies. Biological assays of Vcom1 and Vcom2 revealed them to be cytotoxic to Sf9 insect cell lines, with Vcom1 demonstrating higher potency than Vcom2. The results suggest that they could be further explored as insecticidal agents and confirm earlier general findings that bracelet cyclotides have more potent insecticidal activity than their Möbius relatives. Seven new cyclotide-like sequences were observed in the transcriptome of V. communis, highlighting the Violaceae as a rich source for new cyclotides with potential insecticidal activity. An analysis of sequences flanking the cyclotide domain in the various precursors from V. communis and other Violaceae plants revealed new insights into cyclotide processing and suggested the possibility of two alternative classes of N-terminal processing enzymes for cyclotide biosynthesis.

Nucleation of a key beta-turn promotes cyclotide oxidative folding

Cyclotides are plant-derived peptides characterized by a head-to-tail cyclic backbone and a cystine knot motif comprised of three disulfide bonds. Formation of this motif via in vitro oxidative folding can be challenging and result in misfolded isomers with non-native disulfide connectivities. Here we investigated the effect of β-turn nucleation on cyclotide oxidative folding. Two types of β-turn mimics were grafted into kalata B1 (kB1), individually replacing each of the four β-turns in the folded cyclotide. Insertion of D-Pro-Gly into loop 5 was beneficial to the folding of both cyclic kB1 and a linear form of the peptide. The linear grafted analog folded four-times faster in aqueous conditions than cyclic kB1 in optimized conditions. Additionally, the cyclic analogue folded without the need for redox agents by transitioning through a native-like intermediate that was on-pathway to product formation. Kalata B1 is from the Mobius subfamily of cyclotides. Grafting D-Pro-Gly into loop 5 of cyclotides from two other subfamilies also had a beneficial effect on folding. Our findings demonstrate the importance of a β-turn nucleation site for cyclotide oxidative folding, which could be adopted as a chemical strategy to improve the in vitro folding of diverse cystine-rich peptides.

Production of functional recombinant roseltide rT1 antimicrobial peptide in tobacco plants

Plant-derived peptides represent a promising group of natural compounds with broad industrial and pharmaceutical applications. Low-efficiency production level is the major obstacle to the commercial production of such bioactive peptides. Today, recombinant techniques have been developed for fast and cost-effective production of high-quality peptides for various applications in the chemical and food industries. The roseltide rT1 is a plant peptide with different antimicrobial properties and therapeutic applications in the prevention and treatment of inflammatory lung diseases by inhibiting human neutrophil elastases. Here, we report the expression of functional recombinant roseltide rT1 peptide in tobacco plants. Transgenic plants were generated by the Agrobacterium-mediated transformation method followed by molecular analysis of transgenic plants to demonstrate successful integration and expression of recombinant rT1 peptide. Protein extracts of transgenic plants expressing a single-copy rT1 gene showed efficient antimicrobial properties as verified by growth inhibition of different bacterial strains. Our results illustrate that plant-derived recombinant rT1 peptide is a promising alternative for rapid and cost-effective production of this important antimicrobial peptide for application in therapeutic and food industries.

Study of biologically active peptides from plant materials: A succinct overview

The study of the biological activity of various peptide compounds is a novel research topic, as peptides have extensive applications in a wide range of sectors. Biologically active peptides can be obtained from various sources, including animals, plants, and microorganisms. Plants, on the other hand, have immense promise owing to their diverse chemical structures, each of which has unique characteristics and pharmacological actions. These characteristics set the plant world apart for the development of several drugs and insecticides. Plant-derived peptides perform a wide range of biological functions, including antibacterial, anticancer, antihypertensive, and antioxidant activities. This study shows that Mass spectrometry (MS) is the primary method used to identify proteins and native peptides isolated from tissues and biological fluids. Proteomics and peptidomics are two distinct peptide analysis approaches employed in this context.

Peptide composition analysis, structural characterization, and prediction of iron binding modes of small molecular weight peptides from mung bean

Iron supplementation is a proactive approach to limit instances of iron deficiency anemia. This study is based on the enzymatic hydrolysis and fractionation of mung bean proteins (MBPs) followed by the determination of the Fe2+ chelating activities of these peptide-containing fractions. MBP-Fe complex was generated using a chemical chelation method and subsequently characterized. Following Sephadex G15 separation of MBPs, one of the fractions containing 10 different peptides, demonstrated maximum Fe2+ chelating activity of 39.97 ± 0.07 μg/mg. The sequences of these peptides were determined using liquid chromatography-tandem mass spectrometry. The Fe2+ ion content of the MBP-Fe complex was determined using X-ray photoelectron spectroscopy and 80% of the iron was found to be in Fe2+ oxidation state. After iron chelation, there was an increase in the peptide's particle size, with an average value of 550.67 ± 0.70 nm. This increase in size was attributed to the contributions of the amino proline and glycine, which extended the peptides to form the MBP-Fe complex. Finally, molecular docking studies revealed that Fe2+ mainly bound to carboxy-oxygen of glutamate and aspartate residues of mung bean peptides to form MBP-Fe complex. This research could serve as a scientific foundation for the development of dietary iron supplements using plant-derived peptides.

MFPPDB: a comprehensive multi-functional plant peptide database.

Plants produce a wide range of bioactive peptides as part of their innate defense mechanisms. With the explosive growth of plant-derived peptides, verifying the therapeutic function using traditional experimental methods are resources and time consuming. Therefore, it is necessary to predict the therapeutic function of plant-derived peptides more effectively and accurately with reduced waste of resources and thus expedite the development of plant peptides. We herein developed a repository of plant peptides predicted to have multiple therapeutic functions, named as MFPPDB (multi-functional plant peptide database). MFPPDB including 1,482,409 single or multiple functional plant origin therapeutic peptides derived from 121 fundamental plant species. The functional categories of these therapeutic peptides include 41 different features such as anti-bacterial, anti-fungal, anti-HIV, anti-viral, and anti-cancer. The detailed physicochemical information of these peptides was presented in functional search and physicochemical property search module, which can help users easily access the peptide information by the plant peptide species, ID, and functions, or by their peptide ID, isoelectric point, peptide sequence, and molecular weight through web-friendly interface. We further matched the predicted peptides to nine state-of-the-art curated functional peptide databases and found that at least 293,408 of the peptides possess functional potentials. Overall, MFPPDB integrated a massive number of plant peptides have single or multiple therapeutic functions, which will facilitate the comprehensive research in plant peptidomics. MFPPDB can be freely accessed through http://124.223.195.214:9188/mfppdb/index.

A Broad Review of Plant-Derived Bioactive Peptides to combat Pathogenic Outbreaks - A Future Peptide based Therapeutic Approach

Cyclotides are plant-derived proteins belonging to globular micro proteins (≈ 25 to 30 amino residues long) class with a cyclized head-to-tail backbone and its structure stabilized by the presence of cystine knot by three disulfide bonds. Cyclotides withstand biochemical degradation and are heat resistant compared to other types of peptides. In addition, conserved amino acids in the region of the cystine knot showed strong tolerance towards genetic errors. Interestingly, their topology makes them suitable for oral administration and cellular membrane transportation via crossing cell membranes. Cyclotides have been strongly potent candidates for designing anti-viral plant-derived peptides to combat newly emerged and reemerged outbreaks and also making them natural scaffold for drug development template. From the recent reports, cyclotides have been genetically engineered to study protein-peptide interactions for targeted drug delivery methods. In this study, we are undertaking a review on the discovery, history, role of cyclotides in Plant's defense mechanism and tools to the characterization of cyclotides, membrane binding efficiency of cyclotides, antiviral property and cyclotide scaffold designing.

The effect of plant-derived peptides on the hot-melt stickiness of herbal extracts during spray drying

The aim of this study was to explore plant-derived peptides as carrier material with the function of anti-hot-melt stickiness of traditional Chinese herbal extracts during spray drying. Crataegi fructus extract (CFE) with a severe hot-melt stickiness problem was used as a model drug, and soy peptides (SPT) were screened as the most effective and suitable carrier material among seven plant-derived proteins and peptides which include soy protein isolate, walnut protein and five kinds of peptides (corn peptides, wheat peptides, walnut peptides, rice peptides and SPT). The addition of 15% SPT also exhibited a strong anti-stickiness effect in other four hot-melt sticky herbal extracts from Chinese herbs (Lycii fructus, Corni fructus, Chaenomelis fructus and Mume fructus) since the obtained powder increased from completely sticking to the wall to more than 50% powder yield. The dynamic surface tensions (DST) of CFE decreased consistently with the increase of SPT from 5% to 20%, and DST1000ms had consistent reduction with the addition of SPT from zero to 20%. Meanwhile, the adhesive force of the single droplet at 28 min decreased below 18.5 N. The softening point of the spray-dried powder of CFE added 15% SPT increased by about 40 °C, and the addition of 15% SPT improved the stability which might be similar with the addition of 50% MD based on scanning electron microscope analysis but more efficiently. These findings confirmed that SPT plant-derived could serve as effective and stable carrier material with good anti-stickiness ability during spray drying.

A peptide from wheat germ abolishes the senile osteoporosis by regulating OPG/RANKL/RANK/TRAF6 signaling pathway

BackgroundOxidative stress played a key role in the development of bone brittleness and is an important pathogenic factor of senile osteoporosis. A variety of animal and plant-derived peptides have been shown to have significant anti-osteoporosis effects in vivo and in vitro. PurposeIn this study, we aim to explore the possible mechanism of wheat germ peptide ADWGGPLPH on senile osteoporosis. Study designNaturally, aged rats were used as animal models of senile osteoporosis. MethodsWheat germ peptide ADWGGPLPH was administered from 9-months-old to 21-months-old, and the effect of ADWGGPLPH on preventing senile osteoporosis was evaluated by measuring serum biochemical indexes, bone histomorphometry, bone biomechanics, and other indexes to elucidate the mechanism of ADWGGPLPH in delaying senile osteoporosis by detecting the expression of osteoporosis-related proteins. ResultsThe results showed that ADWGGPLPH could effectively reduce the level of oxidative stress and improve the microstructure and bone mineral density in senile osteoporosis rats. In addition, ADWGGPLPH could improve the proliferation and differentiation activity of osteoblasts and effectively inhibit osteoclasts’ differentiation by regulating the OPG/RANKL/RANK/TRAF6 pathway. ConclusionADWGGPLPH from wheat germ exhibited a notably effect on senile osteoporosis and has a high potential in the development of the nutrient regimen to against senile osteoporosis.

Short Hexapeptide Optimized from Rice-Derived Peptide 1 Shows Promising Anti-hyperuricemia Activities.

Plant-derived peptides are a treasure trove for new-generation anti-hyperuricemia drugs. In the current study, we optimized a short hexapeptide rice-derived peptide 1 (RDP1)-M3 (AAAAGA) according to the anti-hyperuricemia RDP1 peptide identified from rice in our previous research. Results showed that RDP1-M3 exerted better hyperuricemia-alleviating and xanthine oxidase (XOD)-inhibiting potency in mice than RDP1. The biodistribution of RDP1-M3 was also analyzed. RDP1-M3 directly decreased XOD and uric acid levels in vivo and in vitro. In addition, RDP1-M3 reduced the expression of urate transporter 1 and glucose transporter 9, increased the level of organic anion transporter 1, reduced the expression of NOD-like receptor superfamily pyrin 3 inflammasomes, and reduced the levels of interleukin-1β and tumor necrosis factor-α of hyperuricemic mice. Thus, our results indicated that the optimized short hexapeptide RDP1-M3 may be a candidate drug for anti-hyperuricemia.

Bioactive peptides of plant origin: distribution, functionality, and evidence of benefits in food and health.

The multiple functions of peptides released from proteins have immense potential in food and health. In the past few decades, research interest in bioactive peptides of plant origin has surged tremendously, and new plant-derived peptides are continually discovered with advances in extraction, purification, and characterization technology. Plant-derived peptides are mainly extracted from dicot plants possessing bioactive functions, including antioxidant, cholesterol-lowering, and antihypertensive activities. Although the distinct functions are said to depend on the composition and structure of amino acids, the practical or industrial application of plant-derived peptides with bioactive features is still a long way off. In summary, the present review mainly focuses on the state-of-the-art extraction, separation, and analytical techniques, functional properties, mechanism of action, and clinical study of plant-derived peptides. Special emphasis has been placed on the necessity of more pre-clinical and clinical trials to authenticate the health claims of plant-derived peptides.

Morphological studies of self-assembled cyclotides extracted from Viola odorata as novel versatile platforms in biomedical applications.

Self-assembling peptides have attracted researchers' attention recently. They are classified as biomedical materials with unique properties formed in response to environmental conditions. Cyclotides are macrocyclic plant-derived peptides containing 28-37 amino acids that have the ability to self-assemble. Herein, we investigated the effect of pH, time, and temperature on the self-assembling properties of the cyclotides extracted from Viola odorata. For this purpose, the cyclotides were dispersed in aqueous trifluoroacetic acid at pH 2, 4, or 6 and incubated at 25 or 37 °C for 1, 2, 3, 5, 7 or 10 days, and the morphology of the self-assembled structures was identified by optical microscopy, polarized optical microscopy, scanning electron microscopy, transmission electron microscopy, and fluorescence microscopy. At pH 2 and 4, the self-assembly process of cyclotides comprises a number of steps, starting with the formation of spherical peptide nanostructures followed by hierarchically assembled nanotubes, and then shifting to nanofibers after 10 days. At pH 6, amorphous structures were produced even after 10 days. The temperature also could affect the self-assembly mechanism of the cyclotides. At 25 °C, the spherical peptide micelles formed firstly and then merged to form nanotubes, while at 37 °C the cyclotides showed crystallization followed by an increase in length with time. The fluorescence microscopy images showed that the nanotubes could efficiently entrap the hydrophobic molecules of coumarin. This comparative study on the self-assembly of the cyclotides extracted from Viola odorata is the first example exploring the capacity of these cyclotides to adopt precise nanostructures. The nanotubes and nanofibers obtained with these cyclotides might find interesting applications in drug delivery and tissue engineering.

Anti-inflammatory activity of peptides derived from millet bran in vitro and in vivo.

Various food-derived bioactive peptides have been found with potential anti-inflammatory effects. Millet bran peptide is a food-derived bioactive peptide extracted from millet bran, a by-product of millet processing. In this study, the anti-inflammatory effect of millet bran peptides was investigated. A lipopolysaccharide (LPS)-induced RAW264.7 cell and an animal experiment model were established to test the anti-inflammatory activity of millet bran peptides in vitro. As indicated by the results, millet bran peptides could significantly reduce the levels of inflammatory factors, including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and prostaglandin E2 (PGE2), in the LPS-induced RAW264.7 cell. As demonstrated by the animal experiment results, millet bran peptides could mitigate the inflammation of spontaneously hypertensive rats (SHRs). According to the western blotting results, millet bran peptides reduced the phosphorylation level of an extracellular signal-related kinase (ERK), I Kappa B (IKB), p65, and p38 of LPS-induced RAW264.7 cells. As indicated by 16S rDNA sequencing analysis results, millet bran peptides could modify the composition of intestinal microbes. In brief, millet bran peptides could have anti-inflammatory activities in vivo and in vitro and mitigate the inflammation of LPS-induced RAW264.7 cells by regulating the signaling pathways of nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK). The above research has laid a theoretical basis for the application of plant-derived peptides in health food.

In Silico Analysis of Inhibiting Papain-like Protease from SARS-CoV-2 by Using Plant-Derived Peptides.

SARS-CoV-2 is a corona virus that has been the cause for one of the deadliest pandemics of history, started since 2019. Suppressing the activity of the critical enzymes in the SARS-CoV-2 could potentially inhibit a vital step in viral life cycle. Papain-like protease (PLpro) could be regarded as a critical enzyme in viral replication of SARS-CoV-2. In this research, it was aimed to suppress the activity of PLpro enzyme by using potential plant-derived protease inhibitor peptides. For this purpose, 11 plant derived peptides that could potentially inhibit protease activity were selected from literature. The structures of the PLpro and the peptide ligands were acquired from PDB (protein data bank) and after structural optimization, were docked by using HADDOCK 2.4 program. Analyzing the results indicated that VcTI from Veronica hederifolia provides effective molecular interactions at both liable Zn site and classic active site of PLpro, making it a potential inhibitory ligand for this enzyme that could be used for halting the replication of SARS-CoV-2. Molecular dynamic assay confirmed that the selected receptor and ligand complex was stable. Future in vitro and in vivo investigations are required to verify the efficiency of this compound as a potential therapeutic against SARS-CoV-2 infection.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10989-021-10331-8.

An Ultrapotent and Selective Cyclic Peptide Inhibitor of Human β-Factor XIIa in a Cyclotide Scaffold.

Cyclotides are plant-derived peptides with complex structures shaped by their head-to-tail cyclic backbone and cystine knot core. These structural features underpin the native bioactivities of cyclotides, as well as their beneficial properties as pharmaceutical leads, including high proteolytic stability and cell permeability. However, their inherent structural complexity presents a challenge for cyclotide engineering, particularly for accessing libraries of sufficient chemical diversity to design potent and selective cyclotide variants. Here, we report a strategy using mRNA display enabling us to select potent cyclotide-based FXIIa inhibitors from a library comprising more than 1012 members based on the cyclotide scaffold of Momordica cochinchinensis trypsin inhibitor-II (MCoTI-II). The most potent and selective inhibitor, cMCoFx1, has a pM inhibitory constant toward FXIIa with greater than three orders of magnitude selectivity over related serine proteases, realizing specific inhibition of the intrinsic coagulation pathway. The cocrystal structure of cMCoFx1 and FXIIa revealed interactions at several positions across the contact interface that conveyed high affinity binding, highlighting that such cyclotides are attractive cystine knot scaffolds for therapeutic development.

Genome Mining-Based Discovery of Blenny Fish-Derived Peptides Targeting the Mouse κ-Opioid Receptor.

Over the past years, peptides have attracted increasing interest for G protein-coupled receptor (GPCR) drug discovery and development. Peptides occupy a unique chemical space that is not easily accessible for small molecules and antibodies and provide advantages over these ligand classes such as lower toxicity and higher selectivity. The κ-opioid receptor (KOR) is a prototypic GPCR and an appealing therapeutic target for the development of safer and more effective analgesics. Recently, peptides have emerged as analgesic drug candidates with improved side effect profiles. We have previously identified plant-derived peptides, which activate KOR. Based on this precedent, here we relied on publicly available databases to discover novel KOR peptide ligands by genome mining. Using human preprodynorphin as a query, we identified blenny fish-derived peptides, referred to as blenniorphins, capable of binding to and activating KOR with nanomolar affinity and potency, respectively. Additionally, the blenniorphins altered β-arrestin-2 recruitment at the KOR. Our study demonstrates the utility of genome mining to identify peptide GPCR ligands with intriguing pharmacological properties and unveils the potential of blenny fishes as a source for novel KOR ligands.

Plant-Derived Cyclotides Modulate κ-Opioid Receptor Signaling.

Cyclotides are plant-derived disulfide-rich peptides comprising a cyclic cystine knot, which confers remarkable stability against thermal, proteolytic, and chemical degradation. They represent an emerging class of G protein-coupled receptor (GPCR) ligands. In this study, utilizing a screening approach of plant extracts and pharmacological analysis we identified cyclotides from Carapichea ipecacuanha to be ligands of the κ-opioid receptor (KOR), an attractive target for developing analgesics with reduced side effects and therapeutics for multiple sclerosis (MS). This prompted us to verify whether [T20K]kalata B1, a cyclotide in clinical development for the treatment of MS, is able to modulate KOR signaling. T20K bound to and fully activated KOR in the low μM range. We then explored the ability of T20K to allosterically modulate KOR. Co-incubation of T20K with KOR ligands resulted in positive allosteric modulation in functional cAMP assays by altering either the efficacy of dynorphin A1–13 or the potency and efficacy of U50,488 (a selective KOR agonist), respectively. In addition, T20K increased the basal response upon cotreatment with U50,488. In the bioluminescence resonance energy transfer assay T20K negatively modulated the efficacy of U50,488. This study identifies cyclotides capable of modulating KOR and highlights the potential of plant-derived peptides as an opportunity to develop cyclotide-based KOR modulators.

Pathogen- and plant-derived peptides trigger plant immunity

Plants are constantly exposed to pathogens in their immediate environment. Plants sense the invasion of pathogens by recognizing the components including peptide fragments derived from pathogens, known as pathogen-associated molecular patterns (PAMPs). Plants also produce immunogenic peptides called phytocytokines that regulate immune responses. These molecules are recognized by pattern recognition receptors (PRRs) at plasma membrane. Activated PRRs induce a variety of immune responses including production of reactive oxygen species (ROS), induction of Ca2+ influx and activation of mitogen activated protein kinases (MAPKs). Pattern-triggered immunity (PTI) wards off microbes and pests. In this review, we summarize recent our advances in understanding how the peptide fragments are generated and perceived by plant PRRs at cell surface, and the activated PRRs transduce the downstream immune signaling.