A systemic antiviral resistance-inducing protein isolated from Clerodendrum inerme Gaertn. is a polynucleotide:adenosine glycosidase (ribosome-inactivating protein)

Antiviral activity of ribosome inactivating proteins for management of plant viral infection

In nature, plants exhibit various defense mechanisms to protect themselves from viral infection. Reported to harbor virus-inhibiting compounds like Ribosome inactivating proteins (RIPs). It's a matter of how we explore, identify, and utilize RIPs in managing a given stress. RIPs have been found to contain antiviral, anticancer, and neurotoxic effects and are used in various biomedical and agricultural fields. The expression of RIPs could be enhanced in plants to improve their defense against biotic and abiotic stresses. Identification of new RIPs and genetic sequencing led to the development of new phylogenetic theories. Studies on the interaction between RIPs and cells have increased the knowledge regarding the handling of exogenous proteins by cells. The review provides a brief historical preview, classification, mode of action, and broader applications with a special focus on managing plant viral diseases and concerns to mankind.

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.

Therapeutic options in coronavirus treatment

This chapter details the various therapeutic options available for the treatment of the novel coronavirus, SARS-CoV-2, that has brought the world to a standstill. As at 3.53 CEST, June 28, 2020, WHO reported 9,843,073 confirmed cases of COVID-19, with a death toll of 495,760. The rate of the spread of this disease is alarming posing serious threat to the world healthcare system. Clinical investigations and research are on the way for the development of vaccines or antiviral drugs. Despite this effort, no medication has been found to be very effective for its treatment. In this chapter, emphasis was laid on the need for repurposing of antiviral drugs to combat COVID-19 along with other alternatives such as convalescent plasma therapy and exploitation of drugs from medicinal plants and other natural resources.

A comparison of induced antiviral resistance by the phytoprotein CAP-34 and isolate P1f of the rhizobacterium Pseudomonas putida

CAP-34 is a previously reported phytoprotein isolated from Clerodendrum aculeatum (syn. Volkameria aculeata), inducing systemic antiviral resistance against plant virus infection in susceptible plants. This paper compares the resistance inducing efficacy of CAP-34 and a rhizobacterial isolate P1f on tomato (systemic) and tobacco Xanthi-nc (hypersensitive), against tobacco mosaic virus (TMV). The PGPR isolate was identified as an isolate of Pseudomonas putida through molecular and biochemical characterization, and it exhibited PGPR traits such as production of auxin and siderophore. GC-MS examination of the volatiles produced by P1f included several that are implicated in antimicrobial activity, growth promotion and induced systemic resistance. Foliar treatment of tobacco plants with P1f and CAP-34 led to an induced antiviral state in hypersensitive tobacco that persisted for 5 and 3 days, post-treatment, respectively, with a percent reduction in lesion number greater than 90. A higher accumulation of hydrogen peroxide and production of peroxidase enzyme was recorded in P1f-treated leaves, in comparison to those with CAP-34 treatment. The disease incidence in tomato plants treated with CAP-34 and P1f was 30 and 60 percent, respectively, 28dpi. A significant increase was noted in growth parameters such as number of branches and flowers in CAP-34 treated plants, while a significant enhancement in plant height and dry shoot and root weight was observed in P1f-treated set, compared to the control set. ELISA values for the presence of TMV were significantly lower in the infected tomato plants in the treated sets, as compared to the control set, with CAP-34 treatment exhibiting better results as against the P1f-treated set. In the resistant plants from either set, no viral RNA or viral coat protein was detected through RT-PCR and serology. These results suggest that CAP-34 affords more pronounced protection against virus infection compared to the rhizobacterial isolate P1f.

COVID-19 challenges and its therapeutics

COVID-19, an infectious disease, has emerged as one of the leading causes of death worldwide, making it one of the severe public health issues in recent decades. nCoV, the novel SARS coronavirus that causes COVID-19, has brought together scientists in the quest for possible therapeutic and preventive measures. The development of new drugs to manage COVID-19 effectively is a challenging and time-consuming process, thus encouraging extensive investigation of drug repurposing and repositioning candidates. Several medications, including remdesivir, hydroxychloroquine, chloroquine, lopinavir, favipiravir, ribavirin, ritonavir, interferons, azithromycin, capivasertib and bevacizumab, are currently under clinical trials for COVID-19. In addition, several medicinal plants with considerable antiviral activities are potential therapeutic candidates for COVID-19. Statistical data show that the pandemic is yet to slow down, and authorities are placing their hopes on vaccines. Within a short period, four types of vaccines, namely, whole virus, viral vector, protein subunit, and nucleic acid (RNA/DNA), which can confer protection against COVID-19 in different ways, were already in a clinical trial. SARS-CoV-2 variants spread is associated with antibody escape from the virus Spike epitopes, which has grave concerns for viral re-infection and even compromises the effectiveness of the vaccines. Despite these efforts, COVID-19 treatment is still solely based on clinical management through supportive care. We aim to highlight the recent trends in COVID-19, relevant statistics, and clinical findings, as well as potential therapeutics, including in-line treatment methods, preventive measures, and vaccines to combat the prevalence of COVID-19.

A Brief Overview of Potential Treatments for Viral Diseases Using Natural Plant Compounds: The Case of SARS-Cov

The COVID-19 pandemic, as well as the more general global increase in viral diseases, has led researchers to look to the plant kingdom as a potential source for antiviral compounds. Since ancient times, herbal medicines have been extensively applied in the treatment and prevention of various infectious diseases in different traditional systems. The purpose of this review is to highlight the potential antiviral activity of plant compounds as effective and reliable agents against viral infections, especially by viruses from the coronavirus group. Various antiviral mechanisms shown by crude plant extracts and plant-derived bioactive compounds are discussed. The understanding of the action mechanisms of complex plant extract and isolated plant-derived compounds will help pave the way towards the combat of this life-threatening disease. Further, molecular docking studies, in silico analyses of extracted compounds, and future prospects are included. The in vitro production of antiviral chemical compounds from plants using molecular pharming is also considered. Notably, hairy root cultures represent a promising and sustainable way to obtain a range of biologically active compounds that may be applied in the development of novel antiviral agents.

A Simple, Fast and Portable Method for Electrochemical Detection of Adenine Released by Ricin Enzymatic Activity

International authorities classify ricin toxin present in castor seed as a potential agent for use in bioterrorism. Therefore, the detection, identification, and characterization of ricin in various sample matrices are considered necessary actions for risk assessment during a suspected exposure. This study reports a portable electrochemical assay for detecting active ricin based on the adenine electro-oxidation released from herring sperm DNA substrate by its catalytic action. Also, kinetic parameters were calculated, and the values were K_m of 3.14 µM and K_cat 2107 min⁻¹. A linear response was found in optimized experimental conditions for ricin concentrations ranging from 8 to 120 ng/mL, and with a detection limit of 5.14 ng/mL. This proposed detection strategy emphasizes the possibility of field detection of active ricin in food matrices and can be applied to other endonucleolytic activities.

Antiviral Activity of Ribosome-Inactivating Proteins

Ribosome-inactivating proteins (RIPs) are rRNA N-glycosylases from plants (EC 3.2.2.22) that inactivate ribosomes thus inhibiting protein synthesis. The antiviral properties of RIPs have been investigated for more than four decades. However, interest in these proteins is rising due to the emergence of infectious diseases caused by new viruses and the difficulty in treating viral infections. On the other hand, there is a growing need to control crop diseases without resorting to the use of phytosanitary products which are very harmful to the environment and in this respect, RIPs have been shown as a promising tool that can be used to obtain transgenic plants resistant to viruses. The way in which RIPs exert their antiviral effect continues to be the subject of intense research and several mechanisms of action have been proposed. The purpose of this review is to examine the research studies that deal with this matter, placing special emphasis on the most recent findings.

The role of enzymatic activities of antiviral proteins from plants for action against plant pathogens

Antiviral proteins (AVPs) from plants possess multiple activities, such as N-glycosidase, RNase, DNase enzymatic activity, and induce pathogenesis-related proteins, salicylic acid, superoxide dismutase, peroxidase, and catalase. The N-glycosidase activity releases the adenine residues from sarcin/ricin (S/R) loop of large subunit of ribosomes and interfere the host protein synthesis process and this activity has been attributed for antiviral activity in plant. It has been shown that AVP binds directly to viral genome-linked protein of plant viruses and interfere with protein synthesis of virus. AVPs also possess the RNase and DNase like activity and may be targeting nucleic acid of viruses directly. Recently, the antifungal, antibacterial, and antiinsect properties of AVPs have also been demonstrated. Gene encoding for AVPs has been used for the development of transgenic resistant crops to a broad range of plant pathogens and insect pests. However, the cytotoxicity has been observed in transgenic crops using AVP gene in some cases which can be a limiting factor for its application in agriculture. In this review, we have reviewed various aspects of AVPs particularly their characteristics, possible mode of action and application.

COVID-19: Environment concern and impact of Indian medicinal system

The COVID-19 outbreak has came in existence in late December 2019 at Wuhan, China. It is declared as an epidemic by WHO. The rationale of this study is to provide the details regarding prevention, environment concern, social economic consequences, and medicines for COVID-19. Social distancing, screening, lockdown, use of mask and application of sanitizer or soap at regular time interval is the best prevention against COVID-19. The "oral-feces" transmission of COVID-19 is threat to environment. Improper disposal of medical/biomedical and human waste may harm the total environment. Nitrifying-enriched activated sludge i.e. NAS approach can play important role to clean the environment compartments like sludge and waste. COVID-19 has shown impact on social and economic life, but there is no alternate until the drug discovery. In medicine or treatment of COVID-19 point of views, an integrated approach between modern and traditional medicine system may ensure an early prevention of further viral spread. Based on the symptoms of COVID-19, list of herbs and drugs of Indian Medicine System has been searched and reported. To develop the potential drug against COVID-19, the detailed experimentation and clinical trials to be performed for future prospective.

COVID-19: A promising cure for the global panic

The novel Coronavirus disease 2019 (COVID-19) is caused by SARS-CoV-2, which is the causative agent of a potentially fatal disease that is of great global public health concern. The outbreak of COVID-19 is wreaking havoc worldwide due to inadequate risk assessment regarding the urgency of the situation. The COVID-19 pandemic has entered a dangerous new phase. When compared with SARS and MERS, COVID-19 has spread more rapidly, due to increased globalization and adaptation of the virus in every environment. Slowing the spread of the COVID-19 cases will significantly reduce the strain on the healthcare system of the country by limiting the number of people who are severely sick by COVID-19 and need hospital care. Hence, the recent outburst of COVID-19 highlights an urgent need for therapeutics targeting SARS-CoV-2. Here, we have discussed the structure of virus; varying symptoms among COVID-19, SARS, MERS and common flu; the probable mechanism behind the infection and its immune response. Further, the current treatment options, drugs available, ongoing trials and recent diagnostics for COVID-19 have been discussed. We suggest traditional Indian medicinal plants as possible novel therapeutic approaches, exclusively targeting SARS-CoV-2 and its pathways.

Structure and Activity of a Cytosolic Ribosome-Inactivating Protein from Rice

Ribosome-inactivating proteins (RIPs) are cytotoxic enzymes that inhibit protein translation by depurinating ribosomal RNA. Although most plant RIPs are synthesized with leader sequences that sequester them away from the host ribosomes, several RIPs from cereals lack these signal peptides and therefore probably reside in the cytosol near the plant ribosomes. More than 30 RIP genes have been identified in the rice (Oryza sativa spp. japonica) genome, many of them lacking a signal peptide. This paper focuses on a presumed cytosolic type-1 RIP from rice, referred to as OsRIP1. Using 3D modeling it is shown that OsRIP1 structurally resembles other cereal RIPs and has an active site that meets the requirements for activity. Furthermore, localization studies indicate that OsRIP1-eGFP fusion proteins reside in the nucleocytoplasmic space when expressed in epidermal cells of Nicotiana benthamiana or Arabidopsis thaliana suspension cells. Finally, OsRIP1 was recombinantly produced in Escherichia coli and was demonstrated to possess catalytic activity. Interestingly, this recombinant RIP inactivates wheat ribosomes far less efficiently than rabbit ribosomes in an in vitro system. These findings raise some interesting questions concerning the mode of action and physiological role of OsRIP1. This is the first time a RIP from rice is investigated at protein level and is shown to possess biological activity.

Whole-Cell Multiparameter Assay for Ricin and Abrin Activity-Based Digital Holographic Microscopy

Ricin and abrin are ribosome-inactivating proteins leading to inhibition of protein synthesis and cell death. These toxins are considered some of the most potent and lethal toxins against which there is no available antidote. Digital holographic microscopy (DHM) is a time-lapse, label-free, and noninvasive imaging technique that can provide phase information on morphological features of cells. In this study, we employed DHM to evaluate the morphological changes of cell lines during ricin and abrin intoxication. We showed that the effect of these toxins is characterized by a decrease in cell confluence and changes in morphological parameters such as cell area, perimeter, irregularity, and roughness. In addition, changes in optical parameters such as phase-shift, optical thickness, and effective-calculated volume were observed. These effects were completely inhibited by specific neutralizing antibodies. An enhanced intoxication effect was observed for preadherent compared to adherent cells, as was detected in early morphology changes and confirmed by annexin V/propidium iodide (PI) apoptosis assay. Detection of the dynamic changes in cell morphology at initial stages of cell intoxication by DHM emphasizes the highly sensitive and rapid nature of this method, allowing the early detection of active toxins.

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.

Total Body Irradiation Mitigates Inflammation and Extends the Therapeutic Time Window for Anti-Ricin Antibody Treatment against Pulmonary Ricinosis in Mice

Ricin, a highly toxic plant-derived toxin, is considered a potential weapon in biowarfare and bioterrorism due to its pronounced toxicity, high availability, and ease of preparation. Pulmonary exposure to ricin results in the generation of an acute edematous inflammation followed by respiratory insufficiency and death. Massive neutrophil recruitment to the lungs may contribute significantly to ricin-mediated morbidity. In this study, total body irradiation (TBI) served as a non-pharmacological tool to decrease the potential neutrophil-induced lung injury. TBI significantly postponed the time to death of intranasally ricin-intoxicated mice, given that leukopenia remained stable following intoxication. This increase in time to death coincided with a significant reduction in pro-inflammatory marker levels, and led to marked extension of the therapeutic time window for anti-ricin antibody treatment.

Hyperuricaemia, Xanthine Oxidoreductase and Ribosome-Inactivating Proteins from Plants: The Contributions of Fiorenzo Stirpe to Frontline Research

The enzymes called ribosome-inactivating proteins (RIPs) that are able to depurinate nucleic acids and arrest vital cellular functions, including protein synthesis, are still a frontline research field, mostly because of their promising medical applications. The contributions of Stirpe to the development of these studies has been one of the most relevant. After a short biographical introduction, an overview is offered of the main results obtained by his investigations during last 55 years on his main research lines: hyperuricaemia, xanthine oxidoreductase and RIPs.

Quantitative profiling of the in vivo enzymatic activity of ricin reveals disparate depurination of different pulmonary cell types

The plant-derived toxins ricin and abrin, operate by site-specific depurination of ribosomes, which in turn leads to protein synthesis arrest. The clinical manifestation following pulmonary exposure to these toxins is that of a severe lung inflammation and respiratory insufficiency. Deciphering the pathways mediating between the catalytic activity and the developing lung inflammation, requires a quantitative appreciation of the catalytic activity of the toxins, in-vivo. In the present study, we monitored truncated cDNA molecules which are formed by reverse transcription when a depurinated 28S rRNA serves as template. We found that maximal depurination after intranasal exposure of mice to 2LD50 ricin was reached 48h, where nearly 40% of the ribosomes have been depurinated and that depurination can be halted by post-exposure administration of anti-ricin antibodies. We next demonstrated that the effect of ricin intoxication on different cell types populating the lungs differs greatly, and that outstandingly high levels of damage (80% depurination), were observed in particular for pulmonary epithelial cells. Finally, we found that the magnitude of depurination induced by the related plant-derived toxin abrin, was significantly lower in comparison to ricin, and can be attributed mostly to reduced depurination of pulmonary epithelial cells by abrin. This study provides for the first time vital information regarding the scope and timing of the catalytic performance of ricin and abrin in the lungs of intact animals.

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.

BDP-30, a systemic resistance inducer from Boerhaavia diffusa L., suppresses TMV infection, and displays homology with ribosome-inactivating proteins

Root extract of Boerhaavia diffusa L. induced systemic resistance in tobacco against Tobacco mosaic virus. A 30 kDa protein was isolated as the active component, called BDP-30 on the basis of the molecular weight and source plant. BDP-30, a glycoprotein, was found to be temperature and protease resistant. It was basic, possessing a pI greater than 9.0. In-gel proteolytic digestion of BDP-30 generated two peptides that possessed the amino acid sequence KLYDIPPLR and KVTLPYSGNYER by LC/MS/MS. Both peptides shared absolute sequence identity with trichosanthin, a ribosome-inactivating protein from Trichosanthes kirilowii, and a 78 percent and 100 percent homology respectively with an RIP from Bryonia dioica, bryodin. Further, effort was made to look at the fate of TMV in induced resistant Nicotiana tabacum cv. Xanthi, a systemic host of the virus, at specified days after inoculation in control and treated plants. TMV coat protein (CP) was detected by immunoblot 7 days post inoculation up to 21 days in the control set, but not in treated resistant plants. TMV RNA was detected by RT-PCR using TMV-CP specific primers. Resistant tobacco did not show presence of TMV RNA up to 21 days of inoculation. This suggests that BDP-30 may be suppressing TMV replication.

A wheat aminocyclopropane-1-carboxylate oxidase gene, TaACO1, negatively regulates salinity stress in Arabidopsis thaliana

TaACO1 could catalyze ACC into ethylene in vitro. Constitutive expression of TaACO1 in Arabidopsis conferred salt sensitivity, and TaACO1 regulates salt stress mainly via the DREB1/CBF signal transduction pathway. Ethylene signaling plays essential roles in mediating plant responses to biotic and abiotic stresses, besides regulating plant growth and development. The roles of ethylene biosynthesis in abiotic stress, however, remain elusive. In this study, an aminocyclopropane-1-carboxylate oxidase gene, TaACO1, affecting the terminal step in ethylene biosynthesis, was isolated from a salt-tolerant bread wheat introgression line Shanrong No. 3 (SR3) and its effect on salt-stress response was examined. Purified recombinant protein of TaACO1 heterogenously expressed in Escherchia coli could catalyze ACC into ethylene in vitro. TaACO1 transcripts were down-regulated by salt, drought, oxidative stress and ABA. TaACO1-transgenic plants conferred salt sensitivity as judged from the seed germination, cotyledon greening and the relative root growth under salt stress. Constitutive expression of TaACO1 in Arabidopsis increased AtMYB15 expression and suppressed the expression of stress-responsive genes AtRAB18, AtCBF1 and AtCBF3. These findings are helpful in understanding the roles of ethylene biosynthesis in plant salt-stress response.

Comparative induction of 28S ribosomal RNA cleavage by ricin and the trichothecenes deoxynivalenol and T-2 toxin in the macrophage

Ribosome-inactivating proteins (RIPs) and sesquiterpenoid trichothecene mycotoxins are known to bind to eukaryotic ribosomes, inhibit translation and activate mitogen-activated protein kinases. Here we compared the capacities of the RIP ricin to promote 28S ribosomal RNA (rRNA) cleavage with that of the trichothecenes, deoxynivalenol (DON), and T-2 toxin (T-2). In a cell-free model, exposure to ricin at 300 ng/ml for 30 min depurinated yeast 28S rRNA, however, neither DON (< or = 4 microg/ml) nor T-2 (< or = 2 microg/ml) exhibited this N-glycosidase activity. Incubation of RAW 264.7 macrophages with ricin (20-320 ng/ml), DON (250-5000 ng/ml), or T-2 (2-80 ng/ml) for 6 h, however, generated 28S rRNA-specific products consistent with cleavage sites near the 3' terminal end of murine 28S rRNA. Oligonucleotide extension analysis of treated RAW 264.7 cells revealed that ricin evoked 28S rRNA damage at one site in the alpha-sarcin/ricin (S/R)-loop (A4256) and two other sites (A3560 and A4045) in the peptidyl transferase center. Although DON or T-2 did not damage the S/R loop, these trichothecenes did promote cleavage at A3560 and A4045. In addition, incubation of the cells with ricin (> or = 20 ng/ml), DON (> or = 250 ng/ml), or T-2 (> or = 10 ng/ml) induced RNase activity as well as RNase L mRNA and protein expression. These data suggest that only ricin directly damaged 28S rRNA under cell-free conditions but that ricin, DON, and T-2 promoted intracellular 28S rRNA cleavage, potentially by facilitating the action of endogenous RNases and/or by upregulating RNase expression.

Molecular characterization and systemic induction of single-chain ribosome-inactivating proteins (RIPs) in sugar beet (Beta vulgaris) leaves

Sugar beet (Beta vulgaris L.) leaves contain virus-inducible type 1 (single chain) ribosome-inactivating proteins that have been named beetins. The structural and functional characterization, the cellular location, and the potential role of beetins as antiviral agents are reported here. Beetins are formed of a single polypeptide chain with a varying degree of glycosylation and strongly inhibited in vitro protein synthesis in rabbit reticulocyte lysates (IC50=1.15 ng ml(-1)) and a Vicia sativa L. cell-free system (IC50=68 ng ml(-1)) through the single depurination of the large rRNA. Beetins trigger the multidepurination of tobacco mosaic virus (TMV) genomic RNA which underwent extensive degradation upon treatment with acid aniline. Beetins are extracellular proteins that were recovered from the apoplastic fluid. Induction of sugar beet RIPs with either H2O2 or artichoke mottled crinkle virus (AMCV) was observed in leaves distant from the site of application of such elicitors. The external application of purified beetin to sugar leaves prevented infection by AMCV which supports the preliminary hypothesis that beetins could be involved in plant systemic acquired resistance subjected to induction by phytopathogens.

Novel antiviral agents: a medicinal plant perspective

Several hundred plant and herb species that have potential as novel antiviral agents have been studied, with surprisingly little overlap. A wide variety of active phytochemicals, including the flavonoids, terpenoids, lignans, sulphides, polyphenolics, coumarins, saponins, furyl compounds, alkaloids, polyines, thiophenes, proteins and peptides have been identified. Some volatile essential oils of commonly used culinary herbs, spices and herbal teas have also exhibited a high level of antiviral activity. However, given the few classes of compounds investigated, most of the pharmacopoeia of compounds in medicinal plants with antiviral activity is still not known. Several of these phytochemicals have complementary and overlapping mechanisms of action, including antiviral effects by either inhibiting the formation of viral DNA or RNA or inhibiting the activity of viral reproduction. Assay methods to determine antiviral activity include multiple-arm trials, randomized crossover studies, and more compromised designs such as nonrandomized crossovers and pre- and post-treatment analyses. Methods are needed to link antiviral efficacy/potency- and laboratory-based research. Nevertheless, the relative success achieved recently using medicinal plant/herb extracts of various species that are capable of acting therapeutically in various viral infections has raised optimism about the future of phyto-antiviral agents. As this review illustrates, there are innumerable potentially useful medicinal plants and herbs waiting to be evaluated and exploited for therapeutic applications against genetically and functionally diverse viruses families such as Retroviridae, Hepadnaviridae and Herpesviridae

Studies on the anti-mitogenic, anti-phage and hypotensive effects of several ribosome inactivating proteins

An investigation was conducted to compare the anti-mitogenic, anti-phage and hypotensive activities of several ribosome inactivating proteins (RIPs) in order to ascertain whether the RIPs differed in their potencies in the various bioassays. Agrostin, luffin and saporin elicited a dose-dependent suppression of the mitogenic response of murine splenocytes to concanavalin A. The three RIPs were approximately equipotent in this regard, with near maximal inhibition attained at a dose of 83 nM and approximately 50% inhibition at 830 pM. Trichosanthin was slightly more potent than the three aforementioned RIPs. All of these RIPs were capable of inhibiting the replication of phage M13 in the bacterium Escherichia coli, the ranking of potencies being luffin>trichosanthin>agrostin when tested at a concentration of 3.5 microM. The RIPs gelonin and saporin did not exert a conspicuous antiviral effect at the same dose. After intravenous administration into normotensive rats via the external jugular vein, the RIPs saporin, trichosanthin, gelonin and momordin evoked a mild hypotensive response while luffin and agrostin were inactive. The hypotensive response, however, lacked dose dependence. The RIPs trichosanthin, momordin and gelonin did not affect the blood pressure response to angiotensin I. Chemical modification of the arginine residues of the RIPs brought about a reduction in their ability to inhibit cell-free translation. It appears that the ranking of potency of RIPs in one bioassay was different from the rankings in other assays.

A new class of DNA glycosylase/apurinic/apyrimidinic lyases that act on specific adenines in single-stranded DNA

Although the biological function of DNA glycosylases is to protect the genome by removal of potentially cytotoxic or mutagenic bases, this investigation describes the existence of natural DNA glycosylases with activity on undamaged, nonmispaired bases. Gelonin, pokeweed antiviral protein, and ricin, previously described as ribosome-inactivating proteins, are shown to damage single-stranded DNA by removal of a protein-specific set of adenines and cleavage at the resulting abasic sites. Using an oligonucleotide as the substrate reveals that the reaction proceeds via the enzyme-DNA imino intermediate characteristic of DNA glycosylase/AP lyases. The adenine glycosylase activity on single-stranded DNA reported here challenges the concept that a normal base has to be in a mismatch to be specifically removed. By contrast to other glycosylases, these enzymes are expected to damage DNA rather than participate in repair processes. The significance of this DNase activity to the biological function of these plant proteins and to their toxicity to animal cells remains to be determined.