Peptide-based protease inhibitors from plants

Cowpea lipid transfer protein 1 regulates plant defense by inhibiting the cysteine protease of cowpea mosaic virus

Many virus genomes encode proteases that facilitate infection. The molecular mechanism of plant recognition of viral proteases is largely unexplored. Using the system of Vigna unguiculata and cowpea mosaic virus (CPMV), we identified a cowpea lipid transfer protein (LTP1) which interacts with CPMV-encoded 24KPro, a cysteine protease, but not with the enzymatically inactive mutant 24KPro(C166A). Biochemical assays showed that LTP1 inhibited 24KPro proteolytic cleavage of the coat protein precursor large coat protein-small coat protein. Transient overexpression of LTP1 in cowpea reduced CPMV infection, whereas RNA interference-mediated LTP1 silencing increased CPMV accumulation in cowpea. LTP1 is mainly localized in the apoplast of uninfected plant cells, and after CPMV infection, most of the LTP1 is relocated to intracellular compartments, including chloroplast. Moreover, in stable LTP1-transgenic Nicotiana benthamiana plants, LTP1 repressed soybean mosaic virus (SMV) nuclear inclusion a protease activity, and accumulation of SMV was significantly reduced. We propose that cowpea LTP1 suppresses CPMV and SMV accumulation by directly inhibiting viral cysteine protease activity.

Comprehensive characterization of protease inhibiting gene family, cis-regulatory elements, and protein interaction network in linseed and their expression upon bud fly infestation

Linseed, also known as flax is an important oilseed crop with many potential uses in paint, textile, food and pharmaceutical industries. Susceptibility to bud fly (Dasyneura lini Barnes) infestation is a serious biotic concern leading to severe yield penalty in linseed. Protease inhibitors (PIs) are potential candidates that activate during the insect-pest attack and modulate the resistance. In the present study, we explored the PI candidates in the linseed genome and a total of 100 LuPI genes were identified and grouped into five distinct subgroups. The analysis of cis-acting elements revealed that almost all LuPI promoters contain several regulatory elementary related to growth and development, hormonal regulation and stress responses. Across the subfamilies of PIs, the specific domains are consistently found conserved in all protein sequences. The tissue-specific in-silico expression pattern via RNA-seq revealed that all the genes were regulated during different stress. The expression through qRT-PCR of 15 genes revealed the significant up-regulation of LuPI-24, LuPI-40, LuPI-49, LuPI-53, and LuPI-63 upon bud fly infestation in resistant genotype EC0099001 and resistant check variety Neela. This study establishes a foundation resource for comprehending the structural, functional, and evolutionary dimensions of protease inhibitors in linseed.

Bacterial Degradation of Antinutrients in Foods: The Genomic Insight

Antinutrients, also known as anti-nutritional factors (ANFs), are compounds found in many plant-based foods that can limit the bioavailability of nutrients or can act as precursors to toxic substances. ANFs have controversial effects on human health, depending mainly on their concentration. While the positive effects of these compounds are well documented, the dangers they pose and the approaches to avoid them have not been discussed to the same extent. There is no dispute that many ANFs negatively alter the absorption of vitamins, minerals, and proteins in addition to inhibiting some enzyme activities, thus negatively affecting the bioavailability of nutrients in the human body. This review discusses the chemical properties, plant bioavailability, and deleterious effects of anti-minerals (phytates and oxalates), glycosides (cyanogenic glycosides and saponins), polyphenols (tannins), and proteinaceous ANFs (enzyme inhibitors and lectins). The focus of this study is on the possibility of controlling the amount of ANF in food through fermentation. An overview of the most common biochemical pathways for their microbial reduction is provided, showing the genetic basis of these phenomena, including the active enzymes, the optimal conditions of action, and some data on the regulation of their synthesis.

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

Peptides have emerged as key regulators in various physiological processes, including growth, development, stress, and defense responses within plants as well as ecological interactions of plants with microbes and animals. Understanding and harnessing plant peptides can lead to the development of innovative strategies for crop improvement, increasing agricultural productivity, and enhancing resilience to environmental challenges such as drought, pests, and diseases. Moreover, some plant peptides have shown promise in human health applications, with potential therapeutic benefits as ingredients in herbal medicines as well as novel drug leads. The exploration of plant peptides is essential for unraveling the mysteries of plant biology and advancing peptide drug discovery. This short personal commentary provides a very brief overview about the field of plant-derived peptides and a personal word of motivation to increase the number of scientists in pharmacognosy working with these fascinating biomolecules.

Antifungal activity of a trypsin inhibitor from Salvia hispanica L. (chia) seeds against fluconazole-resistant strains of Candida spp. and evaluation of its toxicity in vitro

The incidence of Candida species resistant to traditional antifungal drugs is increasing globally. This issue significantly impacts patients' lives and increases healthcare expenses, confirming the need to develop novel therapeutic strategies. Recently, a thermostable trypsin inhibitor named ShTI (11.558 kDa), which has antibacterial effects on Staphylococcus aureus, was isolated from Salvia hispanica L. (chia) seeds. This study aimed to assess the antifungal effect of ShTI against Candida species and its synergism with fluconazole and to evaluate its mode of action. Preliminary toxicological studies on mouse fibroblasts were also performed. ShTI exhibited antifungal effects against C. parapsilosis (ATCC® 22,019), C. krusei (ATCC® 6258), and six clinical fluconazole-resistant strains of C. albicans (2), C. parapsilosis (2), and C. tropicalis (2). The minimum inhibitory concentration (MIC) values were 4.1 µM (inhibiting 50% of the isolates) and 8.2 µM (inhibiting 100% of the isolates). Additionally, when combined with fluconazole, ShTI had a synergistic effect on C. albicans, altering the morphological structure of the yeast. The mode of action of ShTI against C. krusei (ATCC® 6258) and C. albicans involves cell membrane permeabilization, the overproduction of reactive oxygen species, the formation of pseudohyphae, pore formation, and consequently, cell death. In addition, ShTI (8.65 and 17.3 µM) had noncytotoxic and nongenotoxic effects on L929 mouse fibroblasts. These findings suggest that ShTI could be a promising antimicrobial candidate, but further research is necessary to advance its application as a novel antifungal agent.

Anti-SARS-CoV-2 Viral Activity of Sweet Potato Trypsin Inhibitor via Downregulation of TMPRSS2 Activity and ACE2 Expression In Vitro and In Vivo

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused a global pandemic. Known as COVID-19, it has affected billions of people worldwide, claiming millions of lives and posing a continuing threat to humanity. This is considered one of the most extensive pandemics ever recorded in human history, causing significant losses to both life and economies globally. However, the available evidence is currently insufficient to establish the effectiveness and safety of antiviral drugs or vaccines. The entry of the virus into host cells involves binding to angiotensin-converting enzyme 2 (ACE2), a cell surface receptor, via its spike protein. Meanwhile, transmembrane protease serine 2 (TMPRSS2), a host surface protease, cleaves and activates the virus's S protein, thus promoting viral infection. Plant protease inhibitors play a crucial role in protecting plants against insects and/or microorganisms. The major storage proteins in sweet potato roots include sweet potato trypsin inhibitor (SWTI), which accounts for approximately 60% of the total water-soluble protein and has been found to possess a variety of health-promoting properties, including antioxidant, anti-inflammatory, ACE-inhibitory, and anticancer functions. Our study found that SWTI caused a significant reduction in the expression of the ACE2 and TMPRSS2 proteins, without any adverse effects on cells. Therefore, our findings suggest that the ACE2 and TMPRSS2 axis can be targeted via SWTI to potentially inhibit SARS-CoV-2 infection.

Understanding the mechanism of action of protease inhibitors in controlling the growth of the Candida Genus: potential candidates for development of new antifungal molecules

There is a growing imperative for research into alternative compounds for the treatment of the fungal infections. Thus, many studies have focused on the analysis of antifungal proteins and peptides from different plant sources. Among these molecules are protease inhibitors (PIs). Previously, PIs present in the peptide-rich fractions called PEF1, PEF2 and PEF3 were identified from Capsicum chinense seeds, which have strong activity against phytopathogenic fungi. The aim of this study was to evaluate the mechanism of action and antimicrobial activity of PIs from PEF2 and PEF3 on the growth of yeasts of the genus Candida. In this work, analyses of their antimicrobial activity and cell viability were carried out. Subsequently, the mechanism of action by which the PIs cause the death of the yeasts was evaluated. Cytotoxicity was assessed in vitro by erythrocytes lysis and in vivo in Galleria mellonella larvae. PEF2 and PEF3 caused 100% of the growth inhibition of C. tropicalis and C. buinensis. For C. albicans inhibition was approximately 60% for both fractions. The PEF2 and PEF3 caused a reduction in mitochondrial functionality of 54% and 46% for C. albicans, 26% and 30% for C. tropicalis, and 71% and 68% for C. buinensis, respectively. These fractions induced morphological alterations, led to membrane permeabilization, elevated ROS levels, and resulted in necrotic cell death in C. tropicalis, whilst demonstrating low toxicity toward host cells. From the results obtained here, we intend to contribute to the understanding of the action of PIs in the control of fungal diseases of medical importance.

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 β-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.

A ScWIP5 gene confers fall armyworm resistance by reducing digestive enzyme activities in sugarcane

BACKGROUND

The fall armyworm, Spodoptera frugiperda, is one of the most dangerous pests to various crops. As the most crucial sugar crop, sugarcane is also constantly threatened by these pests. Plant wound-induced proteinase inhibitors (WIP) are natural defense proteins that play important roles in the defense system against insect attack. Breeding for resistance would be the best way to improve the variety characteristics and productivity of sugarcane. Screening and verification for potential plant endogenous insect-resistant genes would greatly improve the insect-resistant breeding progress of sugarcane.

RESULTS

A sugarcane WIP5 gene (ScWIP5) was up-regulated 536 times after insect feeding treatment on previous published transcriptome databases. ScWIP5 was then cloned and its potential role in sugarcane resistance to fall armyworm evaluated by construction of transgenic Nicotiana benthamiana. The toxicity of ScWIP5 transgenic N. benthamiana to fall armyworm showed lower weight gain and higher mortality compared to wild-type N. benthamiana feeding group. Furthermore, the concentration of JA and NbAOC, NbAOS, and NbLOX from the Jasmin acid biosynthesis pathway was significantly induced in ScWIP5 transgenic N. benthamiana compared to the control. In addition, digestive enzyme actives from the insect gut were also evaluated, and trypsin and cathepsin were significantly lower in insects fed with ScWIP5 transgenic N. benthamiana.

CONCLUSION

These results indicate that ScWIP5 might enhance insect resistance by increasing JA signal transduction processes and reducing insect digestive enzyme activities, thus impacting insect growth and development. © 2023 Society of Chemical Industry.

Water-Soluble Coffee Melanoidins Inhibit Digestive Proteases

Coffee is one of the most popular beverages around the world and its consumption contributes to the daily intake of dietary melanoidins. Despite the emerging physiological role of food melanoidins, their effect on digestive processes has not been studied so far. In this study, the activity of the gastrointestinal enzymes pepsin and trypsin was investigated in the presence of water-soluble coffee melanoidins. The gastric enzyme pepsin is only slightly affected, whereas the intestinal enzyme trypsin is severely inhibited by coffee melanoidins. The intestinal digestibility of casein was significantly inhibited by coffee melanoidins at a concentration achievable by regular coffee consumption. The inhibition of proteolytic enzymes by coffee melanoidins might decrease the nutritional value of dietary proteins.

The proteolytic activity in inflammatory bowel disease: insight from gut microbiota

Inflammatory bowel disease (IBD) is a chronic, recurrent inflammatory disease caused by the destruction of the intestinal mucosal epithelium that affects a growing number of people worldwide. Although the etiology of IBD is complex and still elucidated, the role of dysbiosis and dysregulated proteolysis is well recognized. Various studies observed altered composition and diversity of gut microbiota, as well as increased proteolytic activity (PA) in serum, plasma, colonic mucosa, and fecal supernatant of IBD compared to healthy individuals. The imbalance of intestinal microecology and intestinal protein hydrolysis were gradually considered to be closely related to IBD. Notably, the pivotal role of intestinal microbiota in maintaining proteolytic balance received increasing attention. In summary, we have speculated a mesmerizing story, regarding the hidden role of PA and microbiota-derived PA hidden in IBD. Most importantly, we provided the diagnosis and therapeutic targets for IBD as well as the formulation of new treatment strategies for other digestive diseases and protease-related diseases.

Methods for extraction, isolation and sequencing of cyclotides and others cyclic peptides with anti-helminthic activities: An overview

The mortality rate caused by parasitic worms on their hosts is of great concern and studies have been carried out to find molecules to reduce the prevalence, host-parasite interaction, and resistance of parasites to treatments. Existing drugs on the market are very often toxic and have many side effects, hence the need to find new, more active molecules. It has been demonstrated in several works that medicinal plants constitute a wide range of new molecules that can solve this problem. Several works have already been able to demonstrate that cyclic peptides of plant origin have shown good activity in the fight against different types of helminths. Therefore, this review aims to provide a general overview of the methods and techniques of extraction, isolation, activities and mechanisms of action of cyclotides and other cyclic peptides for application in the treatment of helminthic infections.

Combined Omics Approaches Reveal Distinct Mechanisms of Resistance and/or Susceptibility in Sugar Beet Double Haploid Genotypes at Early Stages of Beet Curly Top Virus Infection

Sugar beet is susceptible to Beet curly top virus (BCTV), which significantly reduces yield and sugar production in the semi-arid growing regions worldwide. Sources of genetic resistance to BCTV is limited and control depends upon insecticide seed treatments with neonicotinoids. Through double haploid production and genetic selection, BCTV resistant breeding lines have been developed. Using BCTV resistant (R) [KDH13; Line 13 and KDH4-9; Line 4] and susceptible (S) [KDH19-17; Line 19] lines, beet leafhopper mediated natural infection, mRNA/sRNA sequencing, and metabolite analyses, potential mechanisms of resistance against the virus and vector were identified. At early infection stages (2- and 6-days post inoculation), examples of differentially expressed genes highly up-regulated in the 'R' lines (vs. 'S') included EL10Ac5g10437 (inhibitor of trypsin and hageman factor), EL10Ac6g14635 (jasmonate-induced protein), EL10Ac3g06016 (ribosome related), EL10Ac2g02812 (probable prolyl 4-hydroxylase 10), etc. Pathway enrichment analysis showed differentially expressed genes were predominantly involved with peroxisome, amino acids metabolism, fatty acid degradation, amino/nucleotide sugar metabolism, etc. Metabolite analysis revealed significantly higher amounts of specific isoflavonoid O-glycosides, flavonoid 8-C glycosides, triterpenoid, and iridoid-O-glycosides in the leaves of the 'R' lines (vs. 'S'). These data suggest that a combination of transcriptional regulation and production of putative antiviral metabolites might contribute to BCTV resistance. In addition, genome divergence among BCTV strains differentially affects the production of small non-coding RNAs (sncRNAs) and small peptides which may potentially affect pathogenicity and disease symptom development.

In order to lower the antinutritional activity of serine protease inhibitors, we need to understand their role in seed development

Proteases, including serine proteases, are involved in the entire life cycle of plants. Proteases are controlled by protease inhibitors (PI) to limit any uncontrolled or harmful protease activity. The role of PIs in biotic and abiotic stress tolerance is well documented, however their role in various other plant processes has not been fully elucidated. Seed development is one such area that lack detailed work on the function of PIs despite the fact that this is a key process in the life cycle of the plant. Serine protease inhibitors (SPI) such as the Bowman-Birk inhibitors and Kunitz-type inhibitors, are abundant in legume seeds and act as antinutrients in humans and animals. Their role in seed development is not fully understood and present an interesting research target. Whether lowering the levels and activity of PIs, in order to lower the anti-nutrient levels in seed will affect the development of viable seed, remains an important question. Studies on the function of SPI in seed development are therefore required. In this Perspective paper, we provide an overview on the current knowledge of seed storage proteins, their degradation as well as on the serine protease-SPI system in seeds and what is known about the consequences when this system is modified. We discuss areas that require investigation. This includes the identification of seed specific SPIs; screening of germplasms, to identify plants with low seed inhibitor content, establishing serine protease-SPI ratios and lastly a focus on molecular techniques that can be used to modify seed SPI activity.

Chia (Salvia hispanica L.) Seeds Contain a Highly Stable Trypsin Inhibitor with Potential for Bacterial Management Alone or in Drug Combination Therapy with Oxacillin

The emergence of antibiotic resistance poses a serious and challenging threat to healthcare systems, making it imperative to discover novel therapeutic options. This work reports the isolation and characterization of a thermostable trypsin inhibitor from chia (Salvia hispanica L.) seeds, with antibacterial activity against Staphylococcus aureus sensitive and resistant to methicillin. The trypsin inhibitor ShTI was purified from chia seeds through crude extract heat treatment, followed by affinity and reversed-phase chromatography. Tricine-SDS-PAGE revealed a single glycoprotein band of ~ 11 kDa under nonreducing conditions, confirmed by mass spectrometry analysis (11.558 kDa). ShTI was remarkably stable under high temperatures (100 °C; 120 min) and a broad pH range (2-10; 30 min). Upon exposure to DTT (0.1 M; 120 min), ShTI antitrypsin activity was partially lost (~ 38%), indicating the participation of disulfide bridges in its structure. ShTI is a competitive inhibitor (Ki = 1.79 × 10-8 M; IC50 = 1.74 × 10-8 M) that forms a 1:1 stoichiometry ratio for the ShTI:trypsin complex. ShTI displayed antibacterial activity alone (MICs range from 15.83 to 19.03 µM) and in combination with oxacillin (FICI range from 0.20 to 0.33) against strains of S. aureus, including methicillin-resistant strains. Overproduction of reactive oxygen species and plasma membrane pore formation are involved in the antibacterial action mode of ShTI. Overall, ShTI represents a novel candidate for use as a therapeutic agent for the bacterial management of S. aureus infections.

Antileishmanial effects of Crotalaria spectabilis Roth aqueous extracts on Leishmania amazonensis

Fifteen polar extracts from leaf, seed, pod, stem, flower and root of Crotalaria spectabilis were prepared using aqueous systems, based on the principles of green chemistry, and showed different protease inhibitor (PI) activities on trypsin, papain, pepsin and the extracellular L. amazonensis serine protease (LSPIII). The most pronounced inhibitory effect on LSPIII was observed in leaf (CS-P), root, stem, flower (CS-FPVPP) and pod (CS-VA) extracts. Crotalaria extracts exhibited low cytotoxicity on macrophages; however, they decreased the viability of L. amazonensis promastigotes and amastigotes, as observed in leaf (CS-AE, CS-P, CS-T and CS-PVPP), seed (CS-ST), flower and root (CS-RA) extracts. CS-P was chosen to study PI and secondary metabolites and a 10-12 kDa protein, analyzed by mass spectrometry, was identified as a serine PI homologous with papaya latex serine PI. Glycosylated flavonoids, such as quercetins, vitexin and tricin were the major secondary metabolites of CS-P. The presence of PIs in C. spectabilis is a new finding, especially in other organs than seeds since PIs have been reported only in seed legumes. Besides, this is the first report of antileishmanial activity of C. spectabilis extracts and the identification of serine polypeptide PI and glycosylated flavonoids from leaf.

A review on anti-nutritional factors: unraveling the natural gateways to human health

Humans are constantly facing multiple health challenges from both communicable and non-communicable diseases that significantly affect their health. Additionally, drug resistance or failure has made the situation even worse and poses serious challenges for researchers to develop new drugs. Hence, to address these problems, there is an urgent need to discover and develop timely and long-term-based therapeutic treatments from different sources. One such approach is harnessing the potential of plant secondary metabolites. Plants have been utilized for therapeutic purposes in addition to being used for nutritional benefits. In the last two decades, plant-based drug developments have been one of the effective means of treating human diseases owing to their multiple functions. More recently, anti-nutritional factors (ANFs) have emerged as one of the important targets for novel plant-based drug development due to their multifaceted and potential pharmacological properties. However, their anti-nutritional properties have been the major setback for their limited success in the pharmacological sector. In this review, we provide an overview of ANFs and their beneficial roles in preventing human diseases with multiple case studies. We also highlight the recent developments and applications of ANFs in the food industry, agriculture, and pharmaceutics with future perspectives. Furthermore, we evaluate meta-analyses on ANFs from the last 30 years in relation to their function in human health benefits. This review is an endeavor to reevaluate the merit of these natural compounds and explore their potential for both human and animal health.

Prospecting native and analogous peptides with anti-SARS-CoV-2 potential derived from the trypsin inhibitor purified from tamarind seeds

The study aimed to prospect in silico native and analogous peptides with anti-SARS-CoV-2 potential derived from the trypsin inhibitor purified from tamarind seeds (TTIp). From the most stable theoretical model of TTIp (TTIp 56/287), in silico cleavage was performed for the theoretical identification of native peptides and generation of analogous peptides. The anti-SARS-CoV-2 potential was investigated through molecular dynamics (MD) simulation between the peptides and binding sites of transmembrane serine protease 2 (TMPRSS2), responsible for the entry of SARS-CoV-2 into the host cell. Five native and analogous peptides were obtained and validated through chemical and physical parameters. The best interaction potential energy (IPE) occurred between TMPRSS2 and one of the native peptides obtained by cleavage with trypsin and its analogous peptide. Thus, both peptides showed many hydrophobic residues, a common physical-chemical property among the peptides that inhibit the entry of enveloped viruses, such as SARS-CoV-2, present in specific drugs to treat COVID-19.

Plant Toxic Proteins: Their Biological Activities, Mechanism of Action and Removal Strategies

Plants evolve to synthesize various natural metabolites to protect themselves against threats, such as insects, predators, microorganisms, and environmental conditions (such as temperature, pH, humidity, salt, and drought). Plant-derived toxic proteins are often secondary metabolites generated by plants. These proteins, including ribosome-inactivating proteins, lectins, protease inhibitors, α-amylase inhibitors, canatoxin-like proteins and ureases, arcelins, antimicrobial peptides, and pore-forming toxins, are found in different plant parts, such as the roots, tubers, stems, fruits, buds, and foliage. Several investigations have been conducted to explore the potential applications of these plant proteins by analyzing their toxic effects and modes of action. In biomedical applications, such as crop protection, drug development, cancer therapy, and genetic engineering, toxic plant proteins have been utilized as potentially useful instruments due to their biological activities. However, these noxious metabolites can be detrimental to human health and cause problems when consumed in high amounts. This review focuses on different plant toxic proteins, their biological activities, and their mechanisms of action. Furthermore, possible usage and removal strategies for these proteins are discussed.

Peptide modulators of cell migration: Overview, applications and future development

Cell migration is a key physiological process in the development and homeostasis of multicellular organisms; errors in this complex system can trigger the development of cancer or inflammatory disorders. Therefore, modulating cell migration provides opportunities for drug discovery. Peptides are gaining importance on the global therapeutics market, given their unique properties compared with established small-molecule drugs or biologics. In this review, we identified over 470 peptides modulating cell migration and analyzed their characteristics. Over 95% of these peptides are in the discovery or preclinical stage, because the transition of peptide hits into drug leads often results in a bottleneck in the development process. We summarize chemical strategies in (pre-)clinical development to enhance drug-like properties of bioactive peptides.

Relationship between Protein Digestibility and the Proteolysis of Legume Proteins during Seed Germination

Legume seed protein is an important source of nutrition, but generally it is less digestible than animal protein. Poor protein digestibility in legume seeds and seedlings may partly reflect defenses against herbivores. Protein changes during germination typically increase proteolysis and digestibility, by lowering the levels of anti-nutrient protease inhibitors, activating proteases, and breaking down storage proteins (including allergens). Germinating legume sprouts also show striking increases in free amino acids (especially asparagine), but their roles in host defense or other processes are not known. While the net effect of germination is generally to increase the digestibility of legume seed proteins, the extent of improvement in digestibility is species- and strain-dependent. Further research is needed to highlight which changes contribute most to improved digestibility of sprouted seeds. Such knowledge could guide the selection of varieties that are more digestible and also guide the development of food preparations that are more digestible, potentially combining germination with other factors altering digestibility, such as heating and fermentation. Techniques to characterize the shifts in protein make-up, activity and degradation during germination need to draw on traditional analytical approaches, complemented by proteomic and peptidomic analysis of mass spectrometry-identified peptide breakdown products.

Plant-Derived Compounds and Extracts as Modulators of Plasmin Activity-A Review

Functionality of the fibrinolytic system is based on activity of its central enzyme, plasmin, responsible for the removal of fibrin clots. Besides the hemostasis, fibrinolytic proteins are also involved in many other physiological and pathological processes, including immune response, extracellular matrix degradation, cell migration, and tissue remodeling. Both the impaired and enhanced activity of fibrinolytic proteins may result in serious physiological consequences: prothrombotic state or excessive bleeding, respectively. However, current medicine offers very few options for treating fibrinolytic disorders, particularly in the case of plasmin inhibition. Although numerous attempts have been undertaken to identify natural or to develop engineered fibrinolytic system modulators, structural similarities within serine proteases of the hemostatic system and pleiotropic activity of fibrinolytic proteins constitute a serious problem in discovering anti- or profibrinolytic agents that could precisely affect the target molecules and reduce the risk of side effects. Therefore, this review aims to present a current knowledge of various classes of natural inhibitors and stimulators of the fibrinolytic system being well-defined low-molecular plant secondary metabolites or constituents of plant extracts as well as plant peptides. This work also discusses obstacles caused by low specificity of most of natural compounds and, hence, outlines recent trends in studies aimed at finding more efficient modulators of plasmin activity, including investigation of modifications of natural pharmacophore templates.

Protease inhibitor from Libidibia ferrea seeds attenuates inflammatory and nociceptive responses in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Libidibia ferrea (Mart. ex. Tul.) L.P. Queiroz is a Brazilian native tree locally known as jucá and pau-ferro, and it has been used in folk medicine for relieving, asthma, bronchitis, sore throat, rheumatism, enterocolitis and fever. The anti-inflammatory properties of L. ferrea were confirmed for its stem, fruit, leaves, bark and seeds extracts, however little is known about the natural compounds that may be associated with that response.

AIM OF THIS STUDY

In a normal physiological condition, many enzymes play an important role in catalyzing biological functions. Among them, proteases are of great interest. Although they take part of many biological systems, as the inflammatory process, when deregulated, proteases may cause system malfunctions, such as under- or overproduction of cytokines, or immune cells activation. Thus, protease inhibitors prevent these immune responses by regulating proteases. The objective of this study was to evaluate the anti-inflammatory and anti-nociceptive response of a protease inhibitor purified from L. ferrea seeds (LfTI).

MATERIALS AND METHODS

In vitro (5, 50 and 250 μg/mL of LfTI) and in vivo (0.6, 3 e 15 mg/kg of LfTI) assays were performed. Male Swiss mice weighing 18-25 g were used for cell harvesting and for the in vivo assays. The anti-inflammatory activity was analyzed in vitro by macrophage cytotoxicity, hydrogen peroxide (H₂O₂) production, and cell adhesion assays; and in vivo by leukocyte recruitment, nitric oxide (NO) production, vascular permeability, paw edema and mast cell degranulation assays. The anti-nociceptive activity was evaluated through abdominal writhing test induced by acetic acid and formalin sensitization.

RESULTS

Our results showed that, in vitro, LfTI is not cytotoxic. Also, LfTI (50 μg/mL) inhibited macrophage H₂O₂ production (48.2%), and adhesion (48.4%). LfTI (0.6, 3 e 15 mg/kg) decreased polymorphonuclear cell recruitment dose-dependently, and it inhibited NO production (53%), vascular permeability (40.7%) and paw edema at 3 mg/kg at different time, but it did not inhibit mast cell degranulation. Besides, LfTI did not inhibit either the number of writhing or the licking time in the formalin test in the second phase (inflammatory). However, LfTI (3 mg/kg) inhibited licking time at the first phase (neurogenic) in the formalin sensitization (46.1%).

CONCLUSIONS

Our results show that LfTI has anti-inflammatory and antinociceptive (neurogenic pain) effects, and these effects might be associated with the inhibition of inflammatory proteases and/or protease-activated receptors activation hindering.

The roles of plant proteases and protease inhibitors in drought response: a review

Upon exposure to drought, plants undergo complex signal transduction events with concomitant changes in the expression of genes, proteins and metabolites. For example, proteomics studies continue to identify multitudes of drought-responsive proteins with diverse roles in drought adaptation. Among these are protein degradation processes that activate enzymes and signalling peptides, recycle nitrogen sources, and maintain protein turnover and homeostasis under stressful environments. Here, we review the differential expression and functional activities of plant protease and protease inhibitor proteins under drought stress, mainly focusing on comparative studies involving genotypes of contrasting drought phenotypes. We further explore studies of transgenic plants either overexpressing or repressing proteases or their inhibitors under drought conditions and discuss the potential roles of these transgenes in drought response. Overall, the review highlights the integral role of protein degradation during plant survival under water deficits, irrespective of the genotypes' level of drought resilience. However, drought-sensitive genotypes exhibit higher proteolytic activities, while drought-tolerant genotypes tend to protect proteins from degradation by expressing more protease inhibitors. In addition, transgenic plant biology studies implicate proteases and protease inhibitors in various other physiological functions under drought stress. These include the regulation of stomatal closure, maintenance of relative water content, phytohormonal signalling systems including abscisic acid (ABA) signalling, and the induction of ABA-related stress genes, all of which are essential for maintaining cellular homeostasis under water deficits. Therefore, more validation studies are required to explore the various functions of proteases and their inhibitors under water limitation and their contributions towards drought adaptation.

Precursor genes of Bowman-Birk-type serine proteinase inhibitors comprise multiple inhibitory domains to promote diversity

BACKGROUND

Proteinase inhibitors are important for the regulation of the activity of enzymes essential for the survival and maintenance of all organisms, and they may hold medicinal and agricultural value. Hyacinthus orientalis L. serine protease inhibitors (HOSPIs), belonging to the Bowman-Birk type inhibitor (BBI) family, have strong inhibitory activities against mammalian serine proteinases. This study explored the relationship between gene structure and multiple isoinhibitor production of these diversified BBIs by analyzing sequences of HOSPI precursor genes.

METHODS

Genomic DNA of H. orientalis roots was obtained and fragmented using 13 specific restriction enzymes, which were amplified by inverse and nested polymerase chain reactions, cloned into the pBluescript II SK (+) vector, and directly sequenced using specific primers. HOSPI gene and protein expression were assessed by quantitative real-time PCR and western blot, respectively. Proteinase inhibitory activity of hyacinth bulb extracts was evaluated by fluorescein isothiocyanate-labeled casein.

RESULTS

Four distinct HOSPI precursor genes were identified, encoding 2-4 different HOSPI domains that were surrounded by additional sequences (named head, linker, and tail sequences) and some introns. Moreover, 3' splicing of the linker sequence may occur through introns inserted between linker sequences. HOSPI gene and protein expression was higher during the stem elongation and the flowering periods.

CONCLUSIONS

These results indicate that gene duplication of the HOSPI precursor as a single set, including tandem repeated HOSPI domains, leads to diversity and effective production of mature HOSPIs by posttranslational processing.

GENERAL SIGNIFICANCE

These findings shed light on the diversity of proteinase inhibitors.

An Overview of the Potentialities of Antimicrobial Peptides Derived from Natural Sources

Antimicrobial peptides (AMPs) are constituents of the innate immune system in every kind of living organism. They can act by disrupting the microbial membrane or without affecting membrane stability. Interest in these small peptides stems from the fear of antibiotics and the emergence of microorganisms resistant to antibiotics. Through membrane or metabolic disruption, they defend an organism against invading bacteria, viruses, protozoa, and fungi. High efficacy and specificity, low drug interaction and toxicity, thermostability, solubility in water, and biological diversity suggest their applications in food, medicine, agriculture, animal husbandry, and aquaculture. Nanocarriers can be used to protect, deliver, and improve their bioavailability effectiveness. High cost of production could limit their use. This review summarizes the natural sources, structures, modes of action, and applications of microbial peptides in the food and pharmaceutical industries. Any restrictions on AMPs' large-scale production are also taken into consideration.

Resistant Protein: Forms and Functions

Several global health risks are related to our dietary lifestyle. As a consequence of the overconsumption of ultra-processed and highly digestible protein (150–200% of the recommended value), excess dietary proteins reach the colon, are hydrolysed to peptides and amino acids by bacterial proteases and fermented to various potentially toxic end products. A diet reformulation strategy with reduced protein content in food products appears to be the most effective approach. A potential approach to this challenge is to reduce food digestibility by introducing resistant protein into the diet that could positively influence human health and gut microbiome functionality. Resistant protein is a dietary constituent not hydrolysed by digestive enzymes or absorbed in the human small intestine. The chemical conformation and the amino acid composition strictly influence its structural stability and resistance to in vivo proteolysis and denaturation. Responding to the important gap in our knowledge regarding the digestibility performance of alternative proteins, we hypothesise that resistant proteins can beneficially alter food functionality via their role in improving metabolic properties and health benefits in human nutrition, similar to fibres and resistant starches. A multidisciplinary investigation of resistant protein will generate tremendous scientific impact for other interlinked societal, economic, technological and health and wellbeing aspects of human life.

Lipid oxidation in pathophysiology of atherosclerosis: Current understanding and therapeutic strategies

A marked increase in the global prevalence of ischemic heart disease demands focused research for novel and more effective therapeutic strategies. At present, atherosclerotic cardiovascular disease (ACVD) is the leading cause of the global incidence of heart attacks and a major contributor to many peripheral cardiac diseases. Decades of research have unearthed the complex and multidimensional pathophysiology of ACVD encompassing oxidative stress, redox imbalance, lipid peroxidation, pro-inflammatory signaling, hyperglycemic stress and diabetes mellitus, chronic low-grade inflammation and aging, immune dysregulation, vascular dysfunction, loss of hemostasis, thrombosis, and fluid shear stress. However, the scientific basis of therapeutic interventions using conventional understandings of the disease mechanisms has been subject to renewed scrutiny with novel findings in recent years. This critical review attempts to revise the pathophysiological mechanisms of atherosclerosis using a recent body of literature, with a focus on lipid metabolism and associated cellular and biochemical processes. The comprehensive study encompasses different molecular perspectives in the development and progression of coronary atherosclerosis. The review also summarizes currently prescribed small molecule therapeutics in inflammation and ACVD, and overviews prospective management measures under development including peptides and microRNA therapeutics. The study provides updated insights into the current knowledge of coronary atherosclerosis, and highlights the need for effective prevention, management and development of novel intervention approaches to overcome this chronic epidemic.

Molecular Characterization of Kunitz-Type Protease Inhibitors from Blister Beetles (Coleoptera, Meloidae)

Protease inhibitors are widely studied since the unrestricted activity of proteases can cause extensive organ lesions. In particular, elastase activity is involved in the pathophysiology of acute lung injury, for example during SARS-CoV-2 infection, while serine proteases and thrombin-like proteases are involved in the development and/or pathology of the nervous system. Natural protease inhibitors have the advantage to be reversible and with few side effects and thus are increasingly considered as new drugs. Kunitz-type protease inhibitors (KTPIs), reported in the venom of various organisms, such as wasps, spiders, scorpions, and snakes, have been studied for their potent anticoagulant activity and widespread protease inhibitor activity. Putative KTPI anticoagulants have been identified in transcriptomic resources obtained for two blister beetle species, Lydus trimaculatus and Mylabris variabilis. The KTPIs of L. trimaculatus and M. variabilis were characterized by combined transcriptomic and bioinformatics methodologies. The full-length mRNA sequences were divided on the base of the sequence of the active sites of the putative proteins. In silico protein structure analyses of each group of translational products show the biochemical features of the active sites and the potential protease targets. Validation of these genes is the first step for considering these molecules as new drugs for use in medicine.

Health Benefits of Cereal Grain- and Pulse-Derived Proteins

Pulses and whole grains are considered staple foods that provide a significant amount of calories, fibre and protein, making them key food sources in a nutritionally balanced diet. Additionally, pulses and whole grains contain many bioactive compounds such as dietary fibre, resistant starch, phenolic compounds and mono- and polyunsaturated fatty acids that are known to combat chronic disease. Notably, recent research has demonstrated that protein derived from pulse and whole grain sources contains bioactive peptides that also possess disease-fighting properties. Mechanisms of action include inhibition or alteration of enzyme activities, vasodilatation, modulation of lipid metabolism and gut microbiome and oxidative stress reduction. Consumer demand for plant-based proteins has skyrocketed primarily based on the perceived health benefits and lower carbon footprint of consuming foods from plant sources versus animal. Therefore, more research should be invested in discovering the health-promoting effects that pulse and whole grain proteins have to offer.

Characterization of a thermostable, protease-tolerant inhibitor of α-glycosidase from carrot: A potential oral additive for treatment of diabetes

Inhibiting α-glucosidase activity is important in controlling postprandial hyperglycemia and, thus, helping to manage type-2 diabetes mellitus (T2DM). In the present study, we purified a hypothetical protein of carrots called DCHP (Daucus Carrot hypoglycemic peptide), and their inhibitory effects on α-glucosidase, as well as related mechanisms, were investigated. The recombinant DCHP protein with a molecular weight of 8 kDa showed strong inhibitory activity against α-glycosidase and maintained good stability in solution. DCHP exhibited no inhibitory activity but was tolerant to trypsin and chymotrypsin. Cellular experiments demonstrated that glucose consumption and lactic acid production increased rapidly when treated with DCHP in Caco-2 and HepG2 cells. DCHP crystal was generated, and the crystal structure, which was similar to that of rBTI and consisted of a central α-helix and a two-stranded β-sheet with a unique loop region. The interaction between DCHP and α-glycosidase was investigated by molecular docking and site-directed mutation, which revealed that Glu43, Pro46, Thr47 Thr48 and Gln49 are the key residues in DCHP that inhibit α-glycosidase activity. This work provides potential bioactive peptides as functional foods or nutraceutical supplements in preventing and managing T2DM.

Arginine-containing dipeptides decrease affinity of gut trypsins and compromise soybean pest development

The design and production of molecules capable of mimicking the binding or/and functional sites of proteins inhibitors represent a promising strategy for the exploration and modulation of gut trypsin function in insect pests, specifically Lepidoptera. Here, for the first time, we characterized the trypsin activity present in the gut, performance and development of Anticarsia gemmatalis (Lepidoptera: Noctuidae) larvae when exposed to arginine-containing dipeptides. In silico assessment showed that arginine-containing dipeptides have a greater affinity for the active site of A. gemmatalis trypsins than lysine-containing peptides due to the presence of the double-charged guanidinium group that enhances the interaction at the S1 subsite of trypsins. Furthermore, the inhibitory and anti-insect potential of the peptides was demonstrated through kinetic and larval life cycle parameters, respectively. These dipeptides showed structural stability, binding to the active site, corroborated in vitro (competitive inhibition), and significant reduction of trypsin enzyme activity in the gut, survival, and weight of the A. gemmatalis larvae. Our findings reinforce the idea that small peptides are promising candidates for lepidopteran pest management. The optimization of DI2 and DI1 peptides, enhancing uptake and affinity to trypsins, may turn the use of these molecules feasible in agriculture.

In vitro Inhibition of HIV-1 by Cyclotide-Enriched Extracts of Viola tricolor

Since viral infectious diseases continue to be a global health threat, new antiviral drugs are urgently needed. A unique class of therapeutic compounds are antimicrobial peptides (AMPs). They can be found in humans, bacteria and plants. Plants express a wide variety of such defense peptides as part of their innate immune system to protect from invading pathogens. Cyclotides are non-classical AMPs that share a similar structure. Their unique topology consists of a circular peptide backbone and disulfide bonds. In previous studies they have been attributed to a wide range of biological activities. To identify novel cyclotides with antiviral activity, we established a library of plant extracts largely consisting of cyclotide-rich species and screened them as inhibitors of HIV-1 infection. Subsequent extraction and fractionation revealed four cyclotide-containing subfractions from Viola tricolor with antiviral activity. These subfractions inhibited HIV-1 infection with IC₅₀ values between 0.6 and 11.2 μg/ml, and selectivity indices of up to 8.1. The identification and characterization of antiviral cyclotides and the determination of the antiviral mechanisms may allow to develop novel agents to combat viral infections. Therefore, cyclotides represent a natural source of bioactive molecules with prospects for development as therapeutics.

Virtual screening and molecular dynamics simulation study of plant protease inhibitors against SARS-CoV-2 envelope protein

Due to the outbreak of a new strain of pandemic coronavirus, there is a huge loss of economy and health. In 2021, some vaccines are recommended as emergency licensed vaccines to protect against the virus, and efforts are continuously ongoing to evaluate the vaccine safety measures for licensed vaccines. Recently, there was an increase in the cases of a new variant of coronavirus (omicron). Envelope protein plays an important role in virus packaging and assembly. If viral assembly is blocked, there is less chance of spreading the infection to another cell.In the present study, the plant protease inhibitors (PPIs) were screened against the envelope protein of SARS CoV 2. The structures were downloaded from the protein data bank. The plant protease inhibitors cystatin-I, Eravatmin, squash, Kunitz, Bowman-Birk, Alpha-amylase inhibitors, and potato serine protease inhibitors were screened and out of them Kunitz, alpha-amylase, and squash protease inhibitors have shown maximum binding energy. The molecular dynamics simulation was performed for docked complexes showing the lowest binding energy by NMA (normal mode analysis) to visualize the motion and stability of complexes. These plant-based protease inhibitors are a good target to fight against the new emerging strain of coronavirus because plant extracted compounds are natural and there is fewer side effect than synthetic compounds.

Evaluating the pesticidal impact of plant protease inhibitors: lethal weaponry in the co-evolutionary battle

In the arsenal of plant defense, protease inhibitors (PIs) are well-designed defensive products to counter field pests. PIs are produced in plant tissues by means of 'stable defense metabolite' and triggered on demand as the perception of the signal and well established as a part of plant active defense. PIs have been utilized for approximately four decades, initially as a gene-alone approach that was later replaced by multiple gene pyramiding/gene stacking due to insect adaptability towards the PI alone. By considering the adaptive responses of the pest to the single insecticidal gene, the concept of gene pyramiding gained continuous appreciation for the development of transgenic crops to deal with co-evolving pests. Gene pyramiding approaches are executed to bypass the insect's adaptive responses against PIs. Stacking PIs with additional insecticidal proteins, plastid engineering, recombinant proteinase inhibitors, RNAi-based methods and CRISPR/Cas9-mediated genome editing are the advanced tools and methods for next-generation pest management. Undoubtedly, the domain associated with the mechanism of PIs in the course of plant-pest interactions will occupy a central role for the advancement of more efficient and sustainable pest control strategies. © 2021 Society of Chemical Industry.

Protease Inhibitors from Plants as Therapeutic Agents- A Review

Plant-based diets are a great source of protease inhibitors (PIs). Two of the most well-known families of PIs are Bowman-Birk inhibitors (BBI) and Kunitz-type inhibitors (KTI). The first group acts mainly on trypsin, chymotrypsin, and elastase; the second is on serine, cysteine, and aspartic proteases. PIs can retard or inhibit the catalytic action of enzymes; therefore, they are considered non-nutritional compounds; nevertheless, animal studies and cell line experiments showed promising results of PIs in treating human illnesses such as obesity, cardiovascular diseases, autoimmune diseases, inflammatory processes, and different types of cancer (gastric, colorectal, breast, and lung cancer). Anticarcinogenic activity's proposed mechanisms of action comprise several inhibitory effects at different molecular levels, i.e., transcription, post-transcription, translation, post-translation, and secretion of cancer cells. This work reviews the potential therapeutic applications of PIs as anticarcinogenic and anti-inflammatory agents in human diseases and the mechanisms by which they exert these effects.

Identification of Proteases and Protease Inhibitors in Seeds of the Recalcitrant Forest Tree Species Quercus ilex

Proteases and protease inhibitors have been identified in the recalcitrant species Quercus ilex using in silico and wet methods, with focus on those present in seeds during germination. In silico analyses showed that the Q. ilex transcriptome database contained 2,240 and 97 transcripts annotated as proteases and protease inhibitors, respectively. They belonged to the different families according to MEROPS, being the serine and metallo ones the most represented. The data were compared with those previously reported for other Quercus species, including Q. suber, Q. lobata, and Q. robur. Changes in proteases and protease inhibitors alongside seed germination in cotyledon and embryo axis tissues were assessed using proteomics and in vitro and in gel activity assays. Shotgun (LC-MSMS) analysis of embryo axes and cotyledons in nonviable (NV), mature (T1) and germinated (T3) seeds allowed the identification of 177 proteases and 12 protease inhibitors, mostly represented by serine and metallo types. Total protease activity, as determined by in vitro assays using azocasein as substrate, was higher in cotyledons than in embryo axes. There were not differences in activity among cotyledon samples, while embryo axis peaked at germinated T4 stage. Gel assays revealed the presence of protease activities in at least 10 resolved bands, in the Mr range of 60-260 kDa, being some of them common to cotyledons and embryo axes in either nonviable, mature, and germinated seeds. Bands showing quantitative or qualitative changes upon germination were observed in embryo axes but not in cotyledons at Mr values of 60-140 kDa. Proteomics shotgun analysis of the 10 bands with protease activity supported the results obtained in the overall proteome analysis, with 227 proteases and 3 protease inhibitors identified mostly represented by the serine, cysteine, and metallo families. The combined use of shotgun proteomics and protease activity measurements allowed the identification of tissue-specific (e.g., cysteine protease inhibitors in embryo axes of mature acorns) and stage-specific proteins (e.g., those associated with mobilization of storage proteins accumulated in T3 stage). Those proteins showing differences between nonviable and viable seeds could be related to viability, and those variables between mature and germinated could be associated with the germination process. These differences are observed mostly in embryo axes but not in cotyledons. Among them, those implicated in mobilization of reserve proteins, such as the cathepsin H cysteine protease and Clp proteases, and also the large number of subunits of the CNS and 26S proteasome complex differentially identified in embryos of the several stages suggests that protein degradation via CNS/26S plays a major role early in germination. Conversely, aspartic proteases such as nepenthesins were exclusively identified in NV seeds, so their presence could be used as indicator of nonviability.

Efficient Protein Extraction Protocols for NanoLC-MS/MS Proteomics Analysis of Plant Tissues with High Proteolytic Activity: A Case Study with Pineapple Pulp

Proteomics is an essential tool to uncover the regulatory processes of fruit biology. In fruits with high proteolytic activity, the inhibition of endogenous proteases is key for successful protein extraction. In this chapter, we describe an efficient protocol for total protein extraction to deal with this inconvenience using pineapple pulp as an example. We corroborated the efficacy of our protein extraction protocols by carrying out nano LC-MS/MS analyses using a highly sensitive hybrid mass spectrometer. In doing so, we were able to identify over 3000 proteins in pineapple pulp. Our contribution paves the way for massive comparative proteomics scrutiny in pineapple fruits, as well as others plant tissues with high protease activity such as papaya, fig, and kiwi fruits.

Recent advances in fungal serine protease inhibitors

Four types of antifungal drugs are available that include inhibitors of ergosterol synthesis, of fungal RNA biosynthesis, and of cell wall biosynthesis as well as physiochemical regulators of fungal membrane sterols. Increasing resistance to antifungal drugs can severely limit treatment options of fungal nail infections, vaginal candidiasis, ringworm, blastomycosis, histoplasmosis, and Candida infections of the mouth, throat, and esophagus, among other infections. Development of strategies focused on new fungicides can effectively help tackle troublesome fungal diseases. The virulence and optimal growth of fungi depend on various extracellular secreted factors, among which proteases, such as serine proteases, are of particular interest. A specific extracellular proteolytic system enables fungi to survive and penetrate the tissues. Given the role of fungal proteases in infection, any molecule capable of selectively and specifically inhibiting their activity can lead to the development of potential drugs. Owing to their specific mode of action, fungal protease inhibitors can avoid fungal resistance observed with currently available treatments. Although fungal secreted proteases have been extensively studied as potential virulence factors, our understanding of the substrate specificity of such proteases remains poor. In this review, we summarize the recent advances in the design and development of specific serine protease inhibitors and provide a brief history of the compounds that inhibit fungal serine protease activity.

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 INFORMATION

The online version contains supplementary material available at 10.1007/s10989-021-10331-8.

The direct and indirect effects of bioactive compounds against coronavirus

Emerging viruses are known to pose a threat to humans in the world. COVID‐19, a newly emerging viral respiratory disease, can spread quickly from people to people via respiratory droplets, cough, sneeze, or exhale. Up to now, there are no specific therapies found for the treatment of COVID‐19. In this sense, the rising demand for effective antiviral drugs is stressed. The main goal of the present study is to cover the current literature about bioactive compounds (e.g., polyphenols, glucosinolates, carotenoids, minerals, vitamins, oligosaccharides, bioactive peptides, essential oils, and probiotics) with potential efficiency against COVID‐19, showing antiviral activities via the inhibition of coronavirus entry into the host cell, coronavirus enzymes, as well as the virus replication in human cells. In turn, these compounds can boost the immune system, helping fight against COVID‐19. Overall, it can be concluded that bioactives and the functional foods containing these compounds can be natural alternatives for boosting the immune system and defeating coronavirus.

Multimeric Association of Purified Novel Bowman-Birk Inhibitor From the Medicinal Forage Legume Mucuna pruriens (L.) DC

A Bowman-Birk protease, i.e., Mucuna pruriens trypsin inhibitor (MPTI), was purified from the seeds by 55.702-fold and revealed a single trypsin inhibitor on a zymogram with a specific activity of 202.31 TIU/mg of protein. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under non-reducing conditions, the protease trypsin inhibitor fraction [i.e., trypsin inhibitor non-reducing (TINR)] exhibited molecular weights of 74 and 37 kDa, and under reducing conditions [i.e., trypsin inhibitor reducing (TIR)], 37 and 18 kDa. TINR-37 revealed protease inhibitor activity on native PAGE and 37 and 18 kDa protein bands on SDS-PAGE. TINR-74 showed peaks corresponding to 18.695, 37.39, 56.085, and 74.78 kDa on ultra-performance liquid chromatography (UPLC) coupled with electrospray ionization/quadrupole time-of-flight-mass spectrometry (ESI/QTOF-MS). Similarly, TINR-37 displayed 18.695 and 37.39 kDa peaks. Furthermore, TIR-37 and TIR-18 exhibited peaks corresponding to 37.39 and 18.695 kDa. Multiple peaks observed by the UPLC-ESI/QTOF analysis revealed the multimeric association, confirming the characteristic and functional features of Bowman-Birk inhibitors (BBIs). The multimeric association helps to achieve more stability, thus enhancing their functional efficiency. MPTI was found to be a competitive inhibitor which again suggested that it belongs to the BBI family of inhibitors, displayed an inhibitor constant of 1.3 × 10^-6 M, and further demonstrates potent anti-inflammatory activity. The study provided a comprehensive basis for the identification of multimeric associates and their therapeutic potential, which could elaborate the stability and functional efficiency of the MPTI in the native state from M. pruriens.

Inhibition of Serine Protease, α-Amylase and Growth of Phytopathogenic Fungi by Antimicrobial Peptides from Capsicum chinense Fruits

Plant fungal diseases cause major problems for the global economy. Antimicrobial peptides have aroused great interest in the control of phytopathogens, as they are natural molecules and have a broad spectrum of inhibitory activity. Herein, we have tried to identify and characterize antimicrobial peptides present in fruits of Capsicum chinense and to evaluate their enzymatic and antifungal activities. The retained fraction obtained in the anion exchange chromatography with strong antifungal activity was subjected to molecular exclusion chromatography and obtained four fractions named G1, G2, G3, and G4. The 6.0-kDa protein band of G2 showed similarity with protease inhibitors type II, and it was able to inhibit 100% of trypsin and α-amylase activities. The protein band with approximately 6.5 kDa of G3 showed similarity with sequences of protease inhibitors from genus Capsicum and showed growth inhibition of 48% for Colletotrichum lindemuthianum, 49% for Fusarium lateritium, and 51% for F. solani and F. oxysporum. Additionally, G3 causes morphological changes, membrane permeabilization, and ROS increase in F. oxysporum cells. The 9-kDa protein band of G4 fraction was similar to a nsLTP type 1, and a protein band of 6.5 kDa was similar to a nsLTP type 2. The G4 fraction was able to inhibit 100% of the activities of glycosidases tested and showed growth inhibition of 35 and 50% of F. oxysporum and C. lindemuthianum, respectively. C. chinense fruits have peptides with antifungal activity and enzyme inhibition with biotechnological potential.

Cyclotides Isolated From Violet Plants of Cameroon Are Inhibitors of Human Prolyl Oligopeptidase

Traditional medicine and the use of herbal remedies are well established in the African health care system. For instance, Violaceae plants are used for antimicrobial or anti-inflammatory applications in folk medicine. This study describes the phytochemical analysis and bioactivity screening of four species of the violet tribe Allexis found in Cameroon. Allexis cauliflora, Allexis obanensis, Allexis batangae and Allexis zygomorpha were evaluated for the expression of circular peptides (cyclotides) by mass spectrometry. The unique cyclic cystine-rich motif was identified in several peptides of all four species. Knowing that members of this peptide family are protease inhibitors, the plant extracts were evaluated for the inhibition of human prolyl oligopeptidase (POP). Since all four species inhibited POP activity, a bioactivity-guided fractionation approach was performed to isolate peptide inhibitors. These novel cyclotides, alca 1 and alca 2 exhibited IC₅₀ values of 8.5 and 4.4 µM, respectively. To obtain their amino acid sequence information, combinatorial enzymatic proteolysis was performed. The proteolytic fragments were evaluated in MS/MS fragmentation experiments and the full-length amino acid sequences were obtained by de novo annotation of fragment ions. In summary, this study identified inhibitors of the human protease POP, which is a drug target for inflammatory or neurodegenerative disorders.

Detection of cysteine-rich peptides in Tragia benthamii Baker (Euphorbiaceae) and in vivo antiinflammatory effect in a chick model

Tragia benthamii (TBM) commonly called the climbing nettle is a tropical plant claimed to have numerous anti inflammatory effects in sub Saharan African ethnomedicine which lacks scientific evidence. Aqueous extracts of TBM were further prepurified on a RP-C18 parked solid phase system to obtain 20% aqueous fraction. This fraction was enzymatically and chemically analyzed (by MALDI TOF MS and MS/MS) to contain interesting low molecular weight cysteine-rich stable peptides within the range of 2.5–3.2 KDa. The 20% aqueous fraction was further tested in vivo using carrageenan-induced foot edema (acute inflammation) in seven-day old chicks with diclofenac as reference drug. The cytotoxicity of this active fraction was investigated using the brine shrimp lethality assay. The brine shrimp cytotoxicity assay produced LC50 above 1000 μg/mL. Pretreatment with the TBM extract (30–300 mg/kg, i.p) dose dependently (P<0.01) reduced foot edema with maximal inhibition of 0.253 ± 0.180 (84.3%) at 300 mg/kg body weight, which was comparable to that of diclofenac with inhibition (P<0.05) of 0.410 ± 0.271 (74.5%) at 10 mg/kg body weight. The study has therefore shown for the first time, the detection of cysteine-rich biologically active peptides in T. benthamii and the stable peptide extracts from this ethnomedicinal plant, which is not toxic to Artemia salina, exhibits anti inflammatory activity in a chick in vivo model. This may provide scientific evidence for its use in the treatment of inflammation and pain in traditional medicine. Further in-depth vivo and in vitro studies will be required to investigate its anti inflammatory activity including effect on HUVEC-TERT, the possible inhibition of ICAM-1 surface expression and the mechanism of the anti inflammatory effect.

PINIR: a comprehensive information resource for Pin-II type protease inhibitors

BACKGROUND

Serine protease inhibitors belonging to the Potato type-II Inhibitor family Protease Inhibitors (Pin-II type PIs) are essential plant defense molecules. They are characterized by multiple inhibitory repeat domains, conserved disulfide bond pattern, and a tripeptide reactive center loop. These features of Pin-II type PIs make them potential molecules for protein engineering and designing inhibitors for agricultural and therapeutic applications. However, the diversity in these PIs remains unexplored due to the lack of annotated protein sequences and their functional attributes in the available databases.

RESULTS

We have developed a database, PINIR (Pin-II type PIs Information Resource), by systematic collection and manual annotation of 415 Pin-II type PI protein sequences. For each PI, the number and position for signature sequences are specified: 695 domains, 75 linkers, 63 reactive center loops, and 10 disulfide bond patterns are identified and mapped. Database analysis revealed novel subcategories of PIs, species-correlated occurrence of inhibitory domains, reactive center loops, and disulfide bond patterns. By analyzing linker regions, we predict that alternative processing at linker regions could generate PI variants in the Solanaceae family.

CONCLUSION

PINIR ( https://pinir.ncl.res.in ) provides a web interface for browsing and analyzing the protein sequences of Pin-II type PIs. Information about signature sequences, spatio-temporal expression, biochemical properties, gene sequences, and literature references are provided. Analysis of PINIR depicts conserved species-specific features of Pin-II type PI protein sequences. Diversity in the sequence of inhibitory domains and reactive loops directs potential applications to engineer Pin-II type PIs. The PINIR database will serve as a comprehensive information resource for further research into Pin-II type PIs.

Natural Products Modulating Angiotensin Converting Enzyme 2 (ACE2) as Potential COVID-19 Therapies

The 2019 coronavirus disease (COVID-19) is a potentially fatal multisystemic infection caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Currently, viable therapeutic options that are cost effective, safe and readily available are desired, but lacking. Nevertheless, the pandemic is noticeably of lesser burden in African and Asian regions, where the use of traditional herbs predominates, with such relationship warranting a closer look at ethnomedicine. From a molecular viewpoint, the interaction of SARS-CoV-2 with angiotensin converting enzyme 2 (ACE2) is the crucial first phase of COVID-19 pathogenesis. Here, we review plants with medicinal properties which may be implicated in mitigation of viral invasion either via direct or indirect modulation of ACE2 activity to ameliorate COVID-19. Selected ethnomedicinal plants containing bioactive compounds which may prevent and mitigate the fusion and entry of the SARS-CoV-2 by modulating ACE2-associated up and downstream events are highlighted. Through further experimentation, these plants could be supported for ethnobotanical use and the phytomedicinal ligands could be potentially developed into single or combined preventive therapeutics for COVID-19. This will benefit researchers actively looking for solutions from plant bioresources and help lessen the burden of COVID-19 across the globe.