Description, Distribution, Activity and Phylogenetic Relationship of Ribosome-Inactivating Proteins in Plants, Fungi and Bacteria

Evolution and natural selection of ribosome-inactivating proteins in bacteria, fungi, and plants

Ribosome-inactivating proteins (RIPs) are found in bacteria, fungi, and plants, with a wide range of biological resistances such as anti-fungal, anti-viral, anti-insect, and anti-tumor. They can be roughly divided into proactive defense bacterial or fungal types and passive defense plant types. We identified 1592 RIP genes in bacteria, fungi, and plants. Approximately 88 % of the 764 bacterial RIPs were Shiga or Shiga-like toxins which were exotoxins and could rapidly enter cells to possess strong biotoxicity, and about 98 % of fungal RIPs were predicted as secreted proteins. RIPs were not detected in non-seed plants such as algae, bryophytes, and ferns. However, we found RIPs in some flowering and non-flowering seed plants. The existence of plant RIPs might be related to the structure of seeds or fruits, which might be associated with whether seeds are easy to survive and spread. The evolutionary characteristics of RIPs were different between dicotyledons and monocotyledons. In addition, we also found that RIP2 genes might emerge very early and be plant-specific. Some plant RIP1 genes might evolve from RIP2 genes. This study provides new insights into the evolution of RIPs.

MAP30 and luffin-α: Novel ribosome-inactivating proteins induce plant systemic resistance against plant viruses

Ribosome-inactivating proteins (RIPs) are toxic N-glycosylase that act on eukaryotic and prokaryotic rRNAs, resulting in arrest protein synthesis. RIPs are widely found in higher plant species and display strong antiviral activity. Previous studies have shown that PAP and α-MMC have antiviral activity against TMV. However, the localization of RIPs in plant cells and the mechanism by which RIPs activate plant defense against several plant viruses remain unclear. In this study, we obtained four RIPs (the C-terminal deletion mutant of pokeweed antiviral proteins (PAP-c), alpha-momorcharin (α-MMC), momordica anti-HIV protein of 30 kDa (MAP30) and luffin-α). The subcellular localization results indicated that these four RIPs were located on the plant cell membrane. Heterologous expression of RIPs (PAP-c, α-MMC, MAP30, luffin-α) enhanced tobacco mosaic virus (TMV) resistance in N. benthamiana. Compared with the control treatment, these RIPs significantly reduced the TMV content (149-357 fold) and altered the movement of TMV in the leaves of N. benthamiana. At the same time, heterologous expression of RIPs (MAP30 and luffin-α) could relieve TMV-induced oxidative damage, significantly inducing the expression of plant defense genes including PR1 and PR2. Furthermore, application of these RIPs could inhibit the infection of turnip mosaic virus (TuMV) and potato virus x (PVX). Therefore, this study demonstrated that MAP30 and luffin-α could be considered as new, effective RIPs for controlling plant viruses by activating plant systemic defense.

Xenobiotic-induced ribosomal stress compromises dysbiotic gut barrier aging: A one health perspective

Upon exposure to internal or environmental insults, ribosomes stand sentinel. In particular, stress-driven dysregulation of ribosomal homeostasis is a potent trigger of adverse outcomes in mammalians. The present study assessed whether the ribosomal insult affects the aging process via the regulation of sentinel organs such as the gut. Analyses of the human aging dataset demonstrated that elevated features of ribosomal stress are inversely linked to barrier maintenance biomarkers during the aging process. Ribosome-insulted worms displayed reduced lifespan, which was associated with the disruption of gut barriers. Mechanistically, ribosomal stress-activated Sek-1/p38 signaling, a central platform of ribosomal stress responses, counteracted the gut barrier deterioration through the maintenance of the gut barrier, which was consistent with the results in a murine insult model. However, since the gut-protective p38 signaling was attenuated with aging, the ribosomal stress-induced distress was exacerbated in the gut epithelia and mucosa of the aged animals, subsequently leading to increased bacterial exposure. Moreover, the bacterial community-based evaluation predicted concomitant increases in the abundance of mucosal sugar utilizers and mucin metabolic enzymes in response to ribosomal insult in the aged host. All of the present evidence on ribosomal insulting against the gut barrier integrity from worms to mammals provides new insights into organelle-associated translational modulation of biological longevity in a one health perspective.

Characterization of Lung Injury following Abrin Pulmonary Intoxication in Mice: Comparison to Ricin Poisoning

Abrin is a highly toxic protein obtained from the seeds of the rosary pea plant Abrus precatorius, and it is closely related to ricin in terms of its structure and chemical properties. Both toxins inhibit ribosomal function, halt protein synthesis and lead to cellular death. The major clinical manifestations following pulmonary exposure to these toxins consist of severe lung inflammation and consequent respiratory insufficiency. Despite the high similarity between abrin and ricin in terms of disease progression, the ability to protect mice against these toxins by postexposure antibody-mediated treatment differs significantly, with a markedly higher level of protection achieved against abrin intoxication. In this study, we conducted an in-depth comparison between the kinetics of in vivo abrin and ricin intoxication in a murine model. The data demonstrated differential binding of abrin and ricin to the parenchymal cells of the lungs. Accordingly, toxin-mediated injury to the nonhematopoietic compartment was shown to be markedly lower in the case of abrin intoxication. Thus, profiling of alveolar epithelial cells demonstrated that although toxin-induced damage was restricted to alveolar epithelial type II cells following abrin intoxication, as previously reported for ricin, it was less pronounced. Furthermore, unlike following ricin intoxication, no direct damage was detected in the lung endothelial cell population following abrin exposure. Reduced impairment of intercellular junction molecules following abrin intoxication was detected as well. In contrast, similar damage to the endothelial surface glycocalyx layer was observed for the two toxins. We assume that the reduced damage to the lung stroma, which maintains a higher level of tissue integrity following pulmonary exposure to abrin compared to ricin, contributes to the high efficiency of the anti-abrin antibody treatment at late time points after exposure.

Sapovaccarin-S1 and -S2, Two Type I RIP Isoforms from the Seeds of Saponaria vaccaria L

Type I ribosome-inactivating proteins (RIPs) are plant toxins that inhibit protein synthesis by exerting rRNA N-glycosylase activity (EC 3.2.2.22). Due to the lack of a cell-binding domain, type I RIPs are not target cell-specific. However once linked to antibodies, so called immunotoxins, they are promising candidates for targeted anti-cancer therapy. In this study, sapovaccarin-S1 and -S2, two newly identified type I RIP isoforms differing in only one amino acid, were isolated from the seeds of Saponaria vaccaria L. Sapovaccarin-S1 and -S2 were purified using ammonium sulfate precipitation and subsequent cation exchange chromatography. The determined molecular masses of 28,763 Da and 28,793 Da are in the mass range typical for type I RIPs and the identified amino acid sequences are homologous to known type I RIPs such as dianthin 30 and saporin-S6 (79% sequence identity each). Sapovaccarin-S1 and -S2 showed adenine-releasing activity and induced cell death in Huh-7 cells. In comparison to other type I RIPs, sapovaccarin-S1 and -S2 exhibited a higher thermostability as shown by nano-differential scanning calorimetry. These results suggest that sapovaccarin-S1 and -S2 would be optimal candidates for targeted anti-cancer therapy.

Ribosome inactivating proteins - An unfathomed biomolecule for developing multi-stress tolerant transgenic plants

Transgenic crops would serve as a tool to overcome the forthcoming crisis in food security and environmental safety posed by degrading land and changing global climate. Commercial transgenic crops developed so far focus on single stress; however, sustaining crop yield to ensure food security requires transgenics tolerant to multiple environmental stresses. Here we argue and demonstrate the untapped potential of ribosome inactivating proteins (RIPs), translation inhibitors, as potential transgenes in developing transgenics to combat multiple stresses in the environment. Plant RIPs target the fundamental processes of the cell with very high specificity to the infecting pests. While controlling pathogens, RIPs also cause ectopic expression of pathogenesis-related proteins and trigger systemic acquired resistance. On the other hand, during abiotic stress, RIPs show antioxidant activity and trigger both enzyme-dependent and enzyme-independent metabolic pathways, alleviating abiotic stress such as drought, salinity, temperature, etc. RIPs express in response to specific environmental signals; therefore, their expression obviates additional physiological load on the transgenic plants instead of the constitutive expression. Based on evidence from its biological significance, ecological roles, laboratory- and controlled-environment success of its transgenics, and ethical merits, we unravel the potential of RIPs in developing transgenic plants showing co-tolerance to multiple environmental stresses.

Natural Products with Inhibitory Activity against Human Immunodeficiency Virus Type 1

Infections caused by human immunodeficiency virus (HIV) are considered one of the main public health problems worldwide. Antiretroviral therapy (ART) is the current modality of treatment for HIV-1 infection. It comprises the combined use of several drugs and can decrease the viral load and increase the CD4⁺ T cell count in patients with HIV-1 infection, thereby proving to be an effective modality. This therapy significantly decreases the rate of morbidity and mortality owing to acquired immunodeficiency syndrome (AIDS) and prolongs and improves the quality of life of infected patients. However, nonadherence to ART may increase viral resistance to antiretroviral drugs and transmission of drug-resistant strains of HIV. Therefore, it is necessary to continue research for compounds with anti-HIV-1 activity, exhibiting a potential for the development of an alternative or complementary therapy to ART with low cost and fewer side effects. Natural products and their derivatives represent an excellent option owing to their therapeutic potential against HIV. Currently, the derivatives of natural products available as anti-HIV-1 agents include zidovudine, an arabinonucleoside derivative of the Caribbean marine sponge (Tectitethya crypta), which inhibits the reverse transcriptase of the virus. This was the first antiviral agent approved for treatment of HIV infection. Additionally, bevirimat (isolated from Syzygium claviflorum) and calanolide A (isolated from Calophyllum sp.) are inhibitors of viral maturation and reverse transcription process, respectively. In the present review, we aimed to describe the wide repertoire of natural compounds exhibiting anti-HIV-1 activity that can be considered for designing new therapeutic strategies to curb the HIV pandemic.

Enzymes as a Reservoir of Host Defence Peptides

Host defence peptides (HDPs) are powerful modulators of cellular responses to various types of insults caused by pathogen agents. To date, a wide range of HDPs, from species of different kingdoms including bacteria, plant and animal with extreme diversity in structure and biological activity, have been described. Apart from a limited number of peptides ribosomally synthesized, a large number of promising and multifunctional HDPs have been identified within protein precursors, with properties not necessarily related to innate immunity, consolidating the fascinating hypothesis that proteins have a second or even multiple biological mission in the form of one or more bio-active peptides. Among these precursors, enzymes constitute certainly an interesting group, because most of them are mainly globular and characterized by a fine specific internal structure closely related to their catalytic properties and also because they are yet little considered as potential HDP releasing proteins. In this regard, the main aim of the present review is to describe a panel of HDPs, identified in all canonical classes of enzymes, and to provide a detailed description on hydrolases and their corresponding HDPs, as there seems to exist a striking link between these structurally sophisticated catalysts and their high content in cationic and amphipathic cryptic peptides.

Chemotherapeutic efficacy of cucurmosin for pancreatic cancer as an alternative of gemcitabine: a comparative metabolomic study

Background

As the preferred drug for single chemotherapeutic application in pancreatic cancer, gemcitabine often demonstrated low sensitivity and strong chemotherapy resistance in patients. Therefore, the search for other drugs with high efficiency and low side effects has become of high importance. The aim of this study was to assess the therapeutic effects of cucurmosin on pancreatic cancer as an alternative of gemcitabine and explore its underlying biochemical mechanism.

Methods

The subcutaneous xenograft mice with pancreatic cancer were treated by high- and low-dose cucurmosin and gemcitabine, respectively. A comparative metabolomic analysis was performed on the serum samples from the different groups by 1H nuclear magnetic resonance (NMR) techniques and then subjected to univariate and multivariate statistical analysis.

Results

Cucurmosin demonstrated a dose-dependent inhibition to the pancreatic tumors. High-dose cucurmosin provided similar chemotherapeutic efficacy with gemcitabine by positively regulating pyruvate metabolism, glycolysis or gluconeogenesis, and cysteine and methionine metabolism. Inactivating GFR signaling pathway and further inducing apoptosis of tumor cells are the important mechanism of anti-tumor function of cucurmosin.

Conclusions

Cucurmosin is a promising chemotherapeutic drug for pancreatic cancer. However, the dose selection and surface modification should be optimized according to the stage of pancreatic cancer, and an expanded study in both laboratory and clinical regimes needs to be performed.

Plant-Derived Natural Compounds in Genetic Vaccination and Therapy for HPV-Associated Cancers

Simple Summary

DNA vaccination represents a useful approach for human papillomavirus (HPV) cancer therapy. The therapeutic potential of plant-based natural compounds for control of HPV- associated cancers has been also widely explored. Genetic vaccines for HPV-associated tumors that include plant protein-encoding gene sequences, used alone or in combinations with plant metabolites, are being investigated but are still in their infancy. Main focus of this paper is to provide an overview of the current state of novel therapeutic strategies employing genetic vaccines along with plant-derived compounds and genes. We highlight the importance of multimodality treatment regimen such as combining immunotherapy with plant-derived agents.

Abstract

Antigen-specific immunotherapy and, in particular, DNA vaccination provides an established approach for tackling human papillomavirus (HPV) cancers at different stages. DNA vaccines are stable and have a cost-effective production. Their intrinsic low immunogenicity has been improved by several strategies with some success, including fusion of HPV antigens with plant gene sequences. Another approach for the control of HPV cancers is the use of natural immunomodulatory agents like those derived from plants, that are able to interfere in carcinogenesis by modulating many different cellular pathways and, in some instances, to reduce chemo- and radiotherapy resistance of tumors. Indeed, plant-derived compounds represent, in many cases, an abundantly available, cost-effective source of molecules that can be either harvested directly in nature or obtained from plant cell cultures. In this review, an overview of the most relevant data reported in literature on the use of plant natural compounds and genetic vaccines that include plant-derived sequences against HPV tumors is provided. The purpose is also to highlight the still under-explored potential of multimodal treatments implying DNA vaccination along with plant-derived agents.

An unusual type I ribosome-inactivating protein from Agrostemma githago L

Agrostemma githago L. (corn cockle) is an herbaceous plant mainly growing in Europe. The seeds of the corn cockle are toxic and poisonings were widespread in the past by consuming contaminated flour. The toxic principle of Agrostemma seeds was attributed to triterpenoid secondary metabolites. Indeed, this is in part true. However Agrostemma githago L. is also a producer of ribosome-inactivating proteins (RIPs). RIPs are N-glycosylases that inactivate the ribosomal RNA, a process leading to an irreversible inhibition of protein synthesis and subsequent cell death. A widely known RIP is ricin from Ricinus communis L., which was used as a bioweapon in the past. In this study we isolated agrostin, a 27 kDa RIP from the seeds of Agrostemma githago L., and determined its full sequence. The toxicity of native agrostin was investigated by impedance-based live cell imaging. By RNAseq we identified 7 additional RIPs (agrostins) in the transcriptome of the corn cockle. Agrostin was recombinantly expressed in E. coli and characterized by MALDI-TOF–MS and adenine releasing assay. This study provides for the first time a comprehensive analysis of ribosome-inactivating proteins in the corn cockle and complements the current knowledge about the toxic principles of the plant.

Unexpected Toxicity of Green Tea Polyphenols in Combination with the Sambucus RIL Ebulin

The safety of concentrated food complements intake is a major health concern. It has been well established that green tea polyphenols (GTPs) consumption promotes healthy effects. However, the ingestion of large amounts of GTPs is a matter of controversy due to reported adverse effects. We underwent a preliminary exploration of the effects of the oral administration of a standardized concentrated GTPs preparation on mice which suffered from reversible intestinal derangement promoted by sublethal amounts of the antiribosomal lectin ebulin f from dwarf elder (Sambucus ebulus L.). Neither independent oral administration of 30 mg/kg body weight Polyphenon 60 nor intraperitoneal administration of 2.5 mg/kg body weight ebulin f triggered lethal toxicity. In contrast, the simultaneous administration of these same doses of both Polyphenon 60 and ebulin f triggered an important and unexpected synergistic toxic action featured by the biphasic reduction of weight, which continued after eight days, reaching a reduction of 40%. Lethality appeared 2 days after the onset of the combined treatment and reached more than 50% after 10 days.

Atomic-resolution structures of type I ribosome inactivating protein alpha-momorcharin with different substrate analogs

Alpha-momorcharin (Alpha-MMC) from the seed of bitter melon is a type I ribosome inactivating protein (RIP) that removes a specific adenine from 28S rRNA and inhibits protein biosynthesis. Here, we report seven crystal complex structures of alpha-MMC with different substrate analogs (adenine, AMP, cAMP, dAMP, ADP, GMP, and xanthosine) at 1.08 Å to 1.52 Å resolution. These structures reveal that not only adenine, but also guanine and their analogs can effectively bind to alpha-MMC. The side chain of Tyr93 adopts two conformations, serving as a switch to open and close the substrate binding pocket of alpha-MMC. Although adenine, AMP, GMP, and guanine are located in a similar active site in different RIPs, residues involved in the interaction between RIPs and substrate analogs are slightly different. Complex structures of alpha-MMC with different substrate analogs solved in this study provide useful information on its enzymatic mechanisms and may enable the development of new inhibitors to treat the poisoning of alpha-MMC.

Molecular cloning and in-depth bioinformatics analysis of type II ribosome-inactivating protein isolated from Sambucus ebulus

Plant ribosome-inactivating proteins (RIPs) are N-glycosidases which inhibit protein synthesis through depurination of the ribosomal RNA sequence. Type II RIPs are heterodimer proteins which can bind to cell surfaces. The cytotoxicity of these RIPs is different. Sambucus spp. are a rich source of RIP proteins with different properties. In the present study, a type II RIP was isolated from S. ebulus plant that grows widely in the north of Iran, and different bioinformatics tools were used for the evaluation of physicochemical, functional and 3D protein characteristics. The results showed significant differences among isolated RIP and other Sambucus RIP proteins. The study of these differences can not only expand our insight into the functioning mechanisms of plant RIPs but also provide information about a novel RIP protein with potential biological applications.

How Ricin Damages the Ribosome

Ricin belongs to the group of ribosome-inactivating proteins (RIPs), i.e., toxins that have evolved to provide particular species with an advantage over other competitors in nature. Ricin possesses RNA N-glycosidase activity enabling the toxin to eliminate a single adenine base from the sarcin-ricin RNA loop (SRL), which is a highly conserved structure present on the large ribosomal subunit in all species from the three domains of life. The SRL belongs to the GTPase associated center (GAC), i.e., a ribosomal element involved in conferring unidirectional trajectory for the translational apparatus at the expense of GTP hydrolysis by translational GTPases (trGTPases). The SRL represents a critical element in the GAC, being the main triggering factor of GTP hydrolysis by trGTPases. Enzymatic removal of a single adenine base at the tip of SRL by ricin blocks GTP hydrolysis and, at the same time, impedes functioning of the translational machinery. Here, we discuss the consequences of SRL depurination by ricin for ribosomal performance, with emphasis on the mechanistic model overview of the SRL modus operandi.

Purification of a ribosome-inactivating protein with antioxidation and root developer potencies from Celosia plumosa

Considering Celosia plumosa as a potent antiviral plant, the attempt was made to determine, purify and characterize its proteinaceous antiviral elements against tobacco mosaic virus hypersensitive response on Nicotiana glutinosa. By using 60% ammonium sulphate-precipitation, FPLC-based anion and cation-exchange chromatography in 10 and 50 mM NaCl, size-exclusion chromatography in 50 mM NaCl and SDS-PAGE 10%, a 25 kD antiviral protein with ribosome-inactivating/28S rRNase ability was purified from the leaves of C. plumosa at vegetative growth stage. The purified protein showed FRAP-based antioxidant activity in vitro and caused 1.7-fold and 1.4-fold increases in the growth rate of root system upon carborundum-based application on the root growth medium of N. glutinosa. The present work reports an antiviral protein with ribosome-inactivating, antioxidation and root developer potencies in C. plumosa as an edible or ornamental plant that may be useful in health and agricultural biotechnology in the future.

Influence of Food Matrices on the Stability and Bioavailability of Abrin

Abrin, a highly toxic plant toxin, is a potential bioterror weapon. Work from our laboratory and others have shown that abrin is highly resistant to both thermal and pH inactivation methods. We sought to evaluate the effectiveness of selected food processing thermal inactivation conditions against abrin in economically important food matrices (whole milk, non-fat milk, liquid egg, and ground beef). The effectiveness of toxin inactivation was measured via three different assays: (1) In vitro cell free translation (CFT) assay, (2) Vero cell culture cytotoxicity; and the in vivo mouse intraperitoneal (ip) bioassay. For both whole and non-fat milk, complete inactivation was achieved at temperatures of ≥80 °C for 3 min or 134 °C for 60 s, which were higher than the normal vat/batch pasteurization or the high temperature short time pasteurization (HTST). Toxin inactivation in liquid egg required temperatures of ≥74 °C for 3 min higher than suggested temperatures for scrambled eggs (22% solids) and plain whole egg. Additionally, the ground beef (80:20%) matrix was found to be inhibitory for full toxin activity in the mouse bioassay while retaining some activity in both the cell free translation assay and Vero cell culture cytotoxicity assay.

Fruticulosin: A novel type 2 ribosome-inactivating protein from Abrus fruticulosus seeds that exhibits toxic and antileishmanial activity

Plant ribosome-inactivating proteins (RIPs) are a family of toxins that inhibit protein synthesis. In this study, we have isolated a novel type 2 ribosome-inactivating protein (RIP) present in seeds of the Abrus fruticulosus, named of fruticulosin. Fruticulosin, shows characteristics common to other type 2 RIPs, as specificity by galactosides (d-galactose, N-acetyl-d-galactosamine, and d-lactose), mass of approximately 60 kDa and presence of the of disulfide bonds. The N-terminal amino acid sequence (26 residues) of A-chain fruticulosin, determined by Edman degradation, revealed high similarity of the A-chain with those of other type 2 RIPs. The secondary structure of fruticulosin was analysed by circular dichroism, which showed that fruticulosin contains α-helices (22.3%), β-sheets (43.5%), and random coils and corners (34.2%). Furthermore, fruticulosin showed high toxicity in Artemia sp. (3.12 μg/mL), inhibited in vitro protein synthesis by a cell-free system and showed RNA N-glycosidase activity. Fruticulosin presented biological activities such as agglutination and antileishmanial activity on promastigote forms of Leishmania major.

Fordin: A novel type I ribosome inactivating protein from Vernicia fordii modulates multiple signaling cascades leading to anti-invasive and pro-apoptotic effects in cancer cells in vitro

Fordin, which is derived from Vernicia fordii, is a novel type I ribosome inactivating protein (RIP) with RNA N-glycosidase activity. In the present study, fordin was expressed by Escherichia coli and purified using nickel affinity chromatography. Previous studies have demonstrated RIP toxicity in a variety of cancer cell lines. To understand the therapeutic potential of fordin on tumors, the present study investigated the effects of fordin on the viability of several tumor and normal cell lines. The results demonstrated that fordin induced significant cytotoxicity in four cancer cell lines, compared with the normal cell line. Specifically, profound apoptosis and inhibition of cell invasion were observed following fordin exposure in U-2 OS and HepG2 cells; however, the molecular mechanism underlying the action of RIP remains to be fully elucidated. In the present study, it was found that the anticancer effects of fordin were associated with suppression of the nuclear factor (NF)-κB signaling pathway. In U-2 OS and HepG2 cells, fordin inhibited the expression of inhibitor of NF-κB (IκB) kinase, leading to downregulation of the phosphorylation level of IκB, which quelled the nuclear translocation of NF-κB. Fordin also reduced the mRNA and protein levels of NF-κB downstream targets associated with cell apoptosis and metastasis, particularly B-cell lymphoma-2-related protein A1 (Blf-1) and matrix metalloproteinase (MMP)-9. The inactivation of NF-κB and the reduction in the expression levels of Blf-1 and MMP-9 mediated by fordin were also confirmed by co-treatment with lipopolysaccharide or p65 small interfering RNA. These findings suggested a possible mechanism for the fordin-induced effect on tumor cell death and metastasis. The results of the present study demonstrated the multiple anticancer effects of fordin in U-2 OS and HepG2 cells, in part by inhibiting activation of the NF-κB signaling pathway.

Alpha-momorcharin enhances Tobacco mosaic virus resistance in tobaccoNN by manipulating jasmonic acid-salicylic acid crosstalk

Alpha-momorcharin (α-MMC) is a type-I ribosome inactivating protein (RIP) with a molecular weight of 29 kDa found in plants. This protein has been shown to be effective against a broad range of human viruses and also has anti-tumor activities. However, the mechanism by which α-MMC induces plant defense responses and regulates the N gene to promote resistance to the Tobacco mosaic virus (TMV) is still not clear. By using pharmacological and infection experiments, we found that α-MMC enhances TMV resistance of tobacco plants containing the N gene (tobaccoNN). Our results showed that plants pretreated with 0.5 mg/ml α-MMC could relieve TMV-induced oxidative damage, had enhanced the expression of the N gene and increased biosynthesis of jasmonic acid (JA) and salicylic acid (SA). Moreover, transcription of JA and SA signaling pathway genes were increased, and their expression persisted for a longer period of time in plants pretreated with α-MMC compared with those pretreated with water. Importantly, exogenous application of 1-Aminobenzotriazole (ABT, SA inhibitor) and ibuprofen (JA inhibitor) reduced α-MMC induced plant resistance under viral infection. Thus, our results revealed that α-MMC enhances TMV resistance of tobaccoNN plants by manipulating JA-SA crosstalk.

Purification and functional characterization of recombinant balsamin, a ribosome-inactivating protein from Momordica balsamina

Balsamin, a type I ribosome-inactivating protein (RIP), has been shown to inhibit HIV-1 replication at the translation step. Our recent studies have shown that balsamin also possess anti-tumor, antibacterial and DNase-like activity, however, the amount of natural balsamin in Momordica balsamina seeds is limited and preclinical studies require large quantities of pure, bioactive balsamin. Therefore, in this study, we cloned the balsamin gene, expressed it in E.coli BL21 (DE3) strain and purified it by nickel affinity chromatography. Functional analysis indicated that balsamin exhibits both RNA N-glycosidase activity, releasing the Endo-fragment from rabbit reticulocyte rRNA, and DNase-like activity, converting the supercoiled form of a plasmid into the linear form in a concentration-dependent manner. Analysis of secondary structure revealed that recombinant balsamin mainly consisted of α-helical and random coiled with minimal turns and β-sheets. Recombinant balsamin was found to be stable in the temperature range of 20-60 °C and pH range of 6-9. Antimicrobial assays showed that the minimum inhibitory concentrations of recombinant balsamin for various pathogens ranged between 1.56 and 12.5 μg/ml. Heterologous expression and purification of balsamin carries great importance as it provides an alternative approach for large-scale preparation of biologically active recombinant balsamin, which is difficult from its natural source.

The Plant Ribosome-Inactivating Proteins Play Important Roles in Defense against Pathogens and Insect Pest Attacks

Ribosome-inactivating proteins (RIPs) are toxic N-glycosidases that depurinate eukaryotic and prokaryotic rRNAs, thereby arresting protein synthesis during translation. RIPs are widely found in various plant species and within different tissues. It is demonstrated in vitro and in transgenic plants that RIPs have been connected to defense by antifungal, antibacterial, antiviral, and insecticidal activities. However, the mechanism of these effects is still not completely clear. There are a number of reviews of RIPs. However, there are no reviews on the biological functions of RIPs in defense against pathogens and insect pests. Therefore, in this report, we focused on the effect of RIPs from plants in defense against pathogens and insect pest attacks. First, we summarize the three different types of RIPs based on their physical properties. RIPs are generally distributed in plants. Then, we discuss the distribution of RIPs that are found in various plant species and in fungi, bacteria, algae, and animals. Various RIPs have shown unique bioactive properties including antibacterial, antifungal, antiviral, and insecticidal activity. Finally, we divided the discussion into the biological roles of RIPs in defense against bacteria, fungi, viruses, and insects. This review is focused on the role of plant RIPs in defense against bacteria, fungi, viruses, and insect attacks. The role of plant RIPs in defense against pathogens and insects is being comprehended currently. Future study utilizing transgenic technology approaches to study the mechanisms of RIPs will undoubtedly generate a better comprehending of the role of plant RIPs in defense against pathogens and insects. Discovering additional crosstalk mechanisms between RIPs and phytohormones or reactive oxygen species (ROS) against pathogen and insect infections will be a significant subject in the field of biotic stress study. These studies are helpful in revealing significance of genetic control that can be beneficial to engineer crops tolerance to biotic stress.

Which Plant Proteins Are Involved in Antiviral Defense? Review on In Vivo and In Vitro Activities of Selected Plant Proteins against Viruses

Plants have evolved a variety of defense mechanisms to tackle virus attack. Endogenous plant proteins can function as virus suppressors. Different types of proteins mediate defense responses against plant viruses. Pathogenesis-related (PR) proteins are activated upon pathogen infections or in different stress situations and their production is one of many components in plant defense. Ribosome-inactivating proteins (RIPs) suppress translation by enzymatically damaging ribosomes and they have been found to have antiviral activity. RNA-binding proteins (RBPs) bind to target RNAs via specialized RNA-binding domain and can directly or indirectly function in plant defense system against RNA viruses. Proteins involved in silencing machinery, namely Dicer-like (DCL) proteins, Argonaute (AGO) proteins, and RNA-dependent RNA polymerases (RDRs) confer innate antiviral defense in plants as they are able to degrade foreign RNA of viral origin. This review aims to provide a comprehensive and up-to-date picture of plant proteins participating in antiviral defense. As a result we discuss proteins conferring plant antiviral resistance and their potential future applications in different fields of life including agriculture and medicine.

Curcin C, a novel type I ribosome-inactivating protein from the post-germinating cotyledons of Jatropha curcas

A novel type I ribosome-inactivating protein (RIP), designated as curcin C, was purified from Jatropha curcas, an important feedback source of bio-fuel. Molecular mass and isoelectric point of curcin C were 31.398 kDa and 7.12 as detected by MALTI-TOF assay and capillary electrophoresis assay, respectively. N-terminal sequence and LC-MS/MS analyses confirmed that curcin C is a type I RIP having high homology, but not the exactly the same with curcin, another type 1 RIP isolated from the endosperm of J. curcas. It exhibited N-glycosidase activity and in vitro translation inhibition activity. Moreover, curcin C displayed a strong selectively anti-tumor activity on human cancer cells. Its cytotoxicity against osteosarcoma cell line U20S is even higher than that of Paclitaxel with IC₅₀ of 0.019 μM. Purification and identification of curcin C not only suggested its potential in natural anticancer drug development, but also provide chance to understanding different cytotoxic action among different RIPs.

Ribosome Inactivating Proteins from an evolutionary perspective

Ribosome Inactivating Proteins (RIPs) are rRNA N-glycosidases that inhibit protein synthesis through the elimination of a single adenine residue from 28S rRNA. Many of these toxins have been characterized in depth from a biochemical and molecular point of view. In addition, their potential use in medicine as highly selective toxins is being explored. In contrast, the evolutionary history of RIP encoding genes has remained traditionally underexplored. In recent years, accumulation of large genomic data has fueled research on this issue and revealed unexpected information about the origin and evolution of RIP toxins. In this review we summarize the current evidence available on the occurrence of different evolutionary mechanisms (gene duplication and losses, horizontal gene transfer, synthesis de novo and domain combination) involved in the evolution of the RIP gene family. Finally, we propose a revised nomenclature for RIP genes based on their evolutionary history.

Metazoan Ribosome Inactivating Protein encoding genes acquired by Horizontal Gene Transfer

Ribosome inactivating proteins (RIPs) are RNA N-glycosidases that depurinate a specific adenine residue in the conserved sarcin/ricin loop of 28S rRNA. These enzymes are widely distributed among plants and their presence has also been confirmed in several bacterial species. Recently, we reported for the first time in silico evidence of RIP encoding genes in metazoans, in two closely related species of insects: Aedes aegypti and Culex quinquefasciatus. Here, we have experimentally confirmed the presence of these genes in mosquitoes and attempted to unveil their evolutionary history. A detailed study was conducted, including evaluation of taxonomic distribution, phylogenetic inferences and microsynteny analyses, indicating that mosquito RIP genes derived from a single Horizontal Gene Transfer (HGT) event, probably from a cyanobacterial donor species. Moreover, evolutionary analyses show that, after the HGT event, these genes evolved under purifying selection, strongly suggesting they play functional roles in these organisms.

Novel purification method and antibiotic activity of recombinant Momordica charantia MAP30

Ribosome-inactivating proteins (RIPs) are a group of enzymes originally isolated from plants that possess the ability to damage ribosomes in an irreversible manner, leading to inhibition of protein synthesis in eukaryotic cells. In this study, we aimed to purify recombinant RIPs, investigate their function in the treatment of bacterial infection, and determine their toxicity in mice. We employed a pMAL protein fusion and purification system using E. coli transformed with a plasmid containing MBP-tagged MAP30 cDNA. MBP-tagged MAP30 was purified using a modified novel protocol to effectively produce highly active MAP30 of high purity. In an acute toxicity study in mice, no mortality occurred at doses lower than 1.25 mg/kg. MAP30 at both 0.42 and 0.14 mg/kg induced anti-MAP30 IgG, which reached a maximum titer at week 3. In conclusion, recombinant MAP30 prepared using our purification method possesses bioactivity, and has a synergistic bacteria-killing effect that can significantly reduce the required dosages of chloramphenicol and erythromycin. Therefore, when MAP30 is used in combination with chloramphenicol or erythromycin, it may of benefit in terms of reducing the side effects of the antibiotics, as lower concentrations of antibiotics are required.

Effectively enhancing cytotoxic and apoptotic effects of alpha-momorcharin by integrating a heparin-binding peptide

Alpha-momorcharin (α-MMC), a type I ribosome-inactivating protein, has attracted a great deal of attention because of its antitumor activity. However, the cytotoxicity of α-MMC is limited due to insufficient cellular internalization in cancer cells. To enhance the cytotoxicity of α-MMC, a heparin-binding domain derived from heparin-binding epidermal growth factor (named heparin-binding peptide [HBP]) was used as a cell-penetrating peptide and fused to the C-terminus of α-MMC. This novel α-MMC-HBP fusion protein was expressed and purified with a Ni²⁺ -resin. The N-glycosidase activity and DNase activity assay indicated that the introduction of HBP did not interfere with the intrinsic bioactivities of α-MMC. HBP was able to efficiently carry α-MMC into the tested cancer cells and significantly enhance the cytotoxic effects of α-MMC in a dose-dependent manner. This enhanced cytotoxic ability occurred due to the higher level of cell apoptosis induced by α-MMC-HBP, which was demonstrated in western blot analysis in which α-MMC-HBP triggered caspase 8, caspase 9, casapase 3, and PARP more intensely than α-MMC alone. α-MMC-HBP led to an upregulation of cleaved PARP and an increase in the Bax/Bcl-2 ratio. Our study provided a new practical way to greatly improve the antitumor activity of α-MMC, which could significantly expand the pharmaceutical applications of α-MMC.

Lectin Digestibility and Stability of Elderberry Antioxidants to Heat Treatment In Vitro

Elderberry contains healthy low molecular weight nutraceuticals and lectins which are sequence-related to the elderberry allergen Sam n1. Some of these lectins are type II ribosome-inactivating proteins. The sensitivity of native lectins present in elderberry fruits and bark to the proteolysis triggered by in vitro simulated gastric and duodenal fluids has been investigated. It was found that these lectins are refractory to proteolysis. Nonetheless, incubation for 5-10 min in a boiling water bath completely sensitized them to the hydrolytic enzymes in vitro. Under these conditions neither total Folin-Ciocalteau's reagent reactive compounds, total anthocyanins and the mixture of cyanidin-3-glucoside plus cyanidin-3-sambubioside, nor antioxidant and free-radical scavenging activities were affected by more than 10% for incubations of up to 20 min. Therefore, short-time heat treatment reduces potential allergy-related risks deriving from elderberry consumption without seriously affecting its properties as an antioxidant and free-radical scavenging food.

Ribosome-Inactivating Proteins from Plants: A Historical Overview

This review provides a historical overview of the research on plant ribosome-inactivating proteins (RIPs), starting from the first studies at the end of eighteenth century involving the purification of abrin and ricin, as well as the immunological experiments of Paul Erlich. Interest in these plant toxins was revived in 1970 by the observation of their anticancer activity, which has given rise to a large amount of research contributing to the development of various scientific fields. Biochemistry analyses succeeded in identifying the enzymatic activity of RIPs and allowed for a better understanding of the ribosomal machinery. Studies on RIP/cell interactions were able to detail the endocytosis and intracellular routing of ricin, thus increasing our knowledge of how cells handle exogenous proteins. The identification of new RIPs and the finding that most RIPs are single-chain polypeptides, together with their genetic sequencing, has aided in the development of new phylogenetic theories. Overall, the biological properties of these proteins, including their abortifacient, anticancer, antiviral and neurotoxic activities, suggest that RIPs could be utilized in agriculture and in many biomedical fields, including clinical drug development.

Structures and Ribosomal Interaction of Ribosome-Inactivating Proteins

Ribosome-inactivating proteins (RIPs) including ricin, Shiga toxin, and trichosanthin, are RNA N-glycosidases that depurinate a specific adenine residue (A-4324 in rat 28S ribosomal RNA, rRNA) in the conserved α-sarcin/ricin loop (α-SRL) of rRNA. RIPs are grouped into three types according to the number of subunits and the organization of the precursor sequences. RIPs are two-domain proteins, with the active site located in the cleft between the N- and C-terminal domains. It has been found that the basic surface residues of the RIPs promote rapid and specific targeting to the ribosome and a number of RIPs have been shown to interact with the C-terminal regions of the P proteins of the ribosome. At present, the structural basis for the interaction of trichosanthin and ricin-A chain toward P2 peptide is known. This review surveys the structural features of the representative RIPs and discusses how they approach and interact with the ribosome.

Functional Analysis of a Type-I Ribosome Inactivating Protein Balsamin from Momordica balsamina with Anti-Microbial and DNase Activity

Ribosome inactivating proteins (RIPs) have received considerable attention in biomedical research because of their unique activities towards tumor and virus-infected cells. We extracted balsamin, a type-I RIP, from Momordica balsamina. In the present study, a detailed investigation on DNase activity, antioxidant capacity and antibacterial activity was conducted using purified balsamin. DNase-like activity of balsamin towards plasmid DNA was pH, incubation time and temperature dependent. Moreover, the presence of Mg(2+) (10-50 mM) influenced the DNA cleavage activity. Balsamin also demonstrated reducing power and a capacity to scavenge free radicals in a dose dependent manner. Furthermore, the protein exhibited antibacterial activity against Staphylococcus aureus, Salmonella enterica, Staphylococcus epidermidis and Escherichia coli, which suggests potential utility of balsamin as a nutraceutical.

Biocompatible ELR-Based Polyplexes Coated with MUC1 Specific Aptamers and Targeted for Breast Cancer Gene Therapy

The search for new and biocompatible materials with high potential for improvement is a challenge in gene delivery applications. A cell type specific vector made of elastin-like recombinamer (ELR) and aptamers has been specifically designed for the intracellular delivery of therapeutic material for breast cancer therapy. A lysine-enriched ELR was constructed and complexed with plasmid DNA to give positively charged and stable polyplexes. Physical characterization of these polyplexes showed a particle size of around 140 nm and a zeta potential of approximately +40 mV. The incorporation of MUC1-specific aptamers into the polyplexes resulted in a slight decrease in zeta potential but increased cell transfection specificity for MCF-7 breast cancer cells with respect to a MUC1-negative tumor line. After showing the transfection ability of this aptamer-ELR vector which is facilitated mainly by macropinocytosis uptake, we demonstrated its application for suicide gene therapy using a plasmid containing the gene of the toxin PAP-S. The strategy developed in this work about using ELR as polymeric vector and aptamers as supplier of specificity to deliver therapeutic material into MUC1-positive breast cancer cells shows promising potential and continues paving the way for ELRs in the biomedical field.

Antifungal activity of the ribosome-inactivating protein BE27 from sugar beet (Beta vulgaris L.) against the green mould Penicillium digitatum

The ribosome-inactivating protein BE27 from sugar beet (Beta vulgaris L.) leaves is an apoplastic protein induced by signalling compounds, such as hydrogen peroxide and salicylic acid, which has been reported to be involved in defence against viruses. Here, we report that, at a concentration much lower than that present in the apoplast, BE27 displays antifungal activity against the green mould Penicillium digitatum, a necrotrophic fungus that colonizes wounds and grows in the inter- and intracellular spaces of the tissues of several edible plants. BE27 is able to enter into the cytosol and kill fungal cells, thus arresting the growth of the fungus. The mechanism of action seems to involve ribosomal RNA (rRNA) N-glycosylase activity on the sarcin-ricin loop of the major rRNA which inactivates irreversibly the fungal ribosomes, thus inhibiting protein synthesis. We compared the C-terminus of the BE27 structure with antifungal plant defensins and hypothesize that a structural motif composed of an α-helix and a β-hairpin, similar to the γ-core motif of defensins, might contribute to the specific interaction with the fungal plasma membranes, allowing the protein to enter into the cell.

Ribosome-inactivating proteins (RIPs) and their important health promoting property

Ribosome-inactivating proteins (RIPs), widely present in plants, certain fungi and bacteria, can inhibit protein synthesis by removing one or more specific adenine residues from the large subunit of ribosomal RNAs (rRNAs).

Monoclonal antibody, mAb 4C13, an effective detoxicant antibody against ricin poisoning

Ricin is a glycoprotein produced in castor seeds and consists of two polypeptide chains named Ricin Toxin A Chain (RTA) and Ricin Toxin B Chain (RTB), linked via a disulfide bridge. Due to its high toxicity, ricin is regarded as a high terrorist risk for the public. However, antibodies can play a pivotal role in neutralizing the toxin. In this research, the anti-toxicant effect of mAb 4C13, a monoclonal antibody (mAb) established using detoxicated ricin as the immunized antigen, was evaluated. Compared with mAb 4F2 and mAb 5G6, the effective mechanism of mAb 4C13 was analyzed by experiments relating to its cytotoxicity, epitope on ricin, binding kinetics with the toxin, its blockage on the protein synthesis inhibition induced by ricin and the intracelluar tracing of its complex with ricin. Our result indicated that mAb 4C13 could recognize and bind to RTA, RTB and exert its high affinity to the holotoxin. Both cytotoxicity and animal toxicity of ricin were well blocked by pre-incubating the toxin with mAb 4C13. By intravenous injection, mAb 4C13 could rescue the mouse intraperitoneally (ip) injected with a lethal dose of ricin (20μg/kg) even at 6h after the intoxication and its efficacy was dependent on its dosage. This research indicated that mAb 4C13 could be an excellent candidate for therapeutic antibodies. Its potent antitoxic efficiency was related to its recognition on the specific epitope with very high affinity and its blockage of protein synthesis inhibition in cytoplasm followed by cellular internalization with ricin.

Ribosome-inactivating and related proteins

Ribosome-inactivating proteins (RIPs) are toxins that act as N-glycosidases (EC 3.2.2.22). They are mainly produced by plants and classified as type 1 RIPs and type 2 RIPs. There are also RIPs and RIP related proteins that cannot be grouped into the classical type 1 and type 2 RIPs because of their different sizes, structures or functions. In addition, there is still not a uniform nomenclature or classification existing for RIPs. In this review, we give the current status of all known plant RIPs and we make a suggestion about how to unify those RIPs and RIP related proteins that cannot be classified as type 1 or type 2 RIPs.

Differences in gene expression between natural and artificially induced leaf senescence in barley

Senescence is the last step of leaf development in the life span of an annual plant. Senescence can be induced prematurely by treating leaf tissues with jasmonic acid methyl ester (methyl jasmonate, MeJA). During both senescence programmes, drastic changes occur at the biochemical, cellular and ultra-structural levels that were compared here for primary leaves of barley (Hordeum vulgare L.). Our findings indicate that both types of senescence are similar with respect to the morphological changes including the loss of chlorophyll, disintegration of thylakoids, and formation of plastoglobules. However, the time elapsed for reaching senescence completion was different and ranged from 7 to 8 days for artificially senescing, MeJA-treated plants to 7-8 weeks for naturally senescing plants. Pulse-labelling studies along with RNA and protein gel blot analyses showed differential changes in the expression of both plastid and nuclear genes coding for photosynthetic proteins. Several unique messenger products accumulated in naturally and artificially senescing, MeJA-treated leaves. Detailed expression and crosslinking studies revealed that pheophorbide a oxygenase (PAO), a previously implicated key enzyme of chlorophyll breakdown, is most likely not rate-limiting for chlorophyll destruction under both senescence conditions. Metabolite profiling identified differential changes in the composition of carotenoid derivatives and prenyl-lipids to occur in naturally senescing and artificially senescing plants that underscored the differences between both senescence programmes.

Ebulin from dwarf elder (Sambucus ebulus L.): a mini-review

Sambucus ebulus L. (dwarf elder) is a medicinal plant, the usefulness of which also as food is restricted due to its toxicity. In the last few years, both the chemistry and pharmacology of Sambucus ebulus L. have been investigated. Among the structural and functional proteins present in the plant, sugar-binding proteins (lectins) with or without anti-ribosomal activity and single chain ribosome-inactivating proteins (RIPs) have been isolated. RIPs are enzymes (E.C. 3.2.2.22) that display N-glycosidase activity on the 28S rRNA subunit, leading to the inhibition of protein synthesis by arresting the step of polypeptide chain elongation. The biological role of all these proteins is as yet unknown. The evidence suggests that they could be involved in the defense of the plant against predators and viruses or/and a nitrogen store, with an impact on the nutritional characteristics and food safety. In this mini-review we describe all the isoforms of ebulin that have to date been isolated from dwarf elder, as well as their functional characteristics and potential uses, whilst highlighting concern regarding ebulin toxicity.

Toxicity of the anti-ribosomal Lectin Ebulin f in lungs and intestines in elderly mice

All parts of dwarf elder (Sambucus ebulus L.) studied so far contain a ribosome-inactivating protein with lectin activity (ribosome-inactivating lectin; RIL), known as ebulin. Green fruits contain ebulin f, the toxicity of which has been studied in six-week-old mice, where it was found that the intestines were primary targets for it when administered intraperitoneally (i.p.). We performed experiments to assess whether ebulin f administration to six- and 12-month-old mice would trigger higher toxicity than that displayed in six-week-old mice. In the present report, we present evidence indicating that the toxicological effects of ebulin f after its i.p. administration to elderly mice are exerted on the lungs and intestines by an increased rate of apoptosis. We hypothesize that the ebulin f apoptosis-promoting action together with the age-dependent high rate of apoptosis result in an increase in the lectin’s toxicity, leading to a higher lethality level.