Ribosome-inactivating Protein Type Research Articles

Induction of the PERK-eIF2α-ATF4 Pathway in M1 Macrophages under Endoplasmic Reticulum Stress.

Translation inhibition can activate two cell death pathways. The first pathway is activated by translational aberrations, the second by endoplasmic reticulum (ER) stress. In this work, the effect of ribosome-inactivating protein type II (RIP-II) viscumin on M1 macrophages derived from the THP-1 cell line was investigated. The number of modified ribosomes was evaluated by real-time PCR. Transcriptome analysis revealed that viscumin induces the ER stress activated by the PERK sensor.

Reducing the Immunogenicity of Pulchellin A-Chain, Ribosome-Inactivating Protein Type 2, by Computational Protein Engineering for Potential New Immunotoxins

Pulchellin is a plant biotoxin categorized as a type 2 ribosome-inactivating protein (RIPs) which potentially kills cells at very low concentrations. Biotoxins serve as targeting immunotoxins (IT), consisting of antibodies conjugated to toxins. ITs have two independent protein components, a human antibody and a toxin with a bacterial or plant source; therefore, they pose unique setbacks in immunogenicity. To overcome this issue, the engineering of epitopes is one of the beneficial methods to elicit an immunological response. Here, we predicted the tertiary structure of the pulchellin A-chain (PAC) using five common powerful servers and adopted the best model after refining. Then, predicted structure using four distinct computational approaches identified conformational B-cell epitopes. This approach identified some amino acids as a potential for lowering immunogenicity by point mutation. All mutations were then applied to generate a model of pulchellin containing all mutations (so-called PAM). Mutants’ immunogenicity was assessed and compared to the wild type as well as other mutant characteristics, including stability and compactness, were computationally examined in addition to immunogenicity. The findings revealed a reduction in immunogenicity in all mutants and significantly in N146V and R149A. Furthermore, all mutants demonstrated remarkable stability and validity in Molecular Dynamic (MD) simulations. During docking and simulations, the most homologous toxin to pulchellin, Abrin-A was applied as a control. In addition, the toxin candidate containing all mutations (PAM) disclosed a high level of stability, making it a potential model for experimental deployment. In conclusion, by eliminating B-cell epitopes, our computational approach provides a potential less immunogenic IT based on PAC.

Ricin in Castor Bean (Ricinus communis L.) Seeds: A Review on its Anticancer Activity and The Role of Cytotoxicity Enhancers

Ribosome-inactivating proteins (RIPs) are toxins that are capable to permanently inhibit the synthesis of protein. RIP type II is a heterodimeric protein consisting of an A subunit linked to a lectin-like B chain by a disulfide bridge. Ricin contained in the seeds of Ricinus communis L. is a type II RIP which possesses cytotoxicity activity. However, due to the non-selectivity of the B-lectin chain, ricin needs delivering-vehicles to enhance its cytotoxicity. This article is devoted to reviewing the anticancer activity of ricin in castor bean seeds (a plant type II RIPs) and its various types of cytotoxicity enhancers.

Therapeutic Application of Genetically Engineered Ribosome-Inactivating Toxin Proteins for Cancer

Recently, Ribosome-Inactivating Proteins (RIPs) as a class of anticancer medicines have garnered considerable attention due to their novel anticancer mechanism. Although the medications are small, RIPs utilize the Large-Size Effect (LSE) to block the efflux procedure that are regulated through Drug Resistance Transporters (DRTs), and protect host cells from drug transfection. There are many significant challenges for their therapeutic applications that seriously restrict their usefulness, particularly their strategy towards tumor cells. The primary objective of this review is to emphasize Trichosanthin (TCS) along with Gelonin (Gel) and additional types of RIPs, particularly scorpion venom-derived RIPs, to demonstrate that they should be grappling through what kinds of bio-barriers to overcome in cancer therapeutic science. Next, we will emphasize the latest state-of-the-art in providing cancer treatment RIPs.

New ribosome-inactivating proteins and other proteins with protein synthesis-inhibiting activities.

Ribosome-inactivating proteins (RIPs) consist of three varieties. Type 1 RIPs are single-chained and approximately 30-kDa in molecular weight. Type 2 RIPs are double-chained and composed of a type 1 RIP chain and a lectin chain. Type III RIPs, such as maize b-32 barley and JIP60 which are produced as single-domain proenzymes, possess an N-terminal domain corresponding to the A domain of RIPs and fused to a C-terminal domain. In addition to the aforementioned three types of RIPs originating from flowering plants, there are recently discovered proteins and peptides with ribosome-inactivating and protein synthesis inhibitory activities but which are endowed with characteristics such as molecular weights distinctive from those of the regular RIPs. These new/unusual RIPs discussed in the present review encompass metazoan RIPs from Anopheles and Culex mosquitos, antimicrobial peptides derived from RIP of the pokeweed Phytolacca dioica, maize RIP (a type III RIP derived from a precursor form), RIPs from the garden pea and the kelp. In addition, RIPs with a molecular weight smaller than those of regular type 1 RIPs are produced by plants in the Cucurbitaceae family including the bitter gourd, bottle gourd, sponge gourd, ridge gourd, wax gourd, hairy gourd, pumpkin, and Chinese cucumber. A small type II RIP from camphor tree (Cinnamomum camphora) seeds and a snake gourd type II RIP with its catalytic chain cleaved into two have been reported. RIPs produced from mushrooms including the golden needle mushroom, king tuber mushroom, straw mushroom, and puffball mushroom are also discussed in addition to a type II RIP from the mushroom Polyporus umbellatus. Bacterial (Spiroplasma) RIPs associated with the fruitfly, Shiga toxin, and Streptomyces coelicolor RIP are also dealt with. The aforementioned proteins display a diversity of molecular weights, amino acid sequences, and mechanisms of action. Some of them are endowed with exploitable antipathogenic activities.

Targeted suicide gene transfections reveal promising results in nu/nu mice with aggressive neuroblastoma

Neuroblastoma represents the third most common malign neoplasm occurring in children and the most common in newborn. Although mortality in childhood cancer declined in the last decade, high-risk patients have poor prospects, due to the aggressiveness of the cancer. In the recent past, we underlined the potential of sapofectosid as novel and efficient transfection enhancer, demonstrating non-toxic gene delivery, but its value in tumor therapies has yet to be elucidated. A suicide gene, coding for saporin, a ribosome-inactivating protein type I, was incorporated into targeted, peptide-based nanoplexes. The nanoplexes were characterized for their size, zeta potential and appearance by electron microscopy. Gene delivery was observed via confocal imaging. In vitro transfections were conducted to monitor the real-time cell viability. After initial tolerability studies, NMRI nu/nu-mice bearing tumors from Neuro-2A-Luc-cells (murine neuroblastoma cells, transduced with a luciferase gene), were treated with targeted nanoplexes (30 μg saporin-DNA i.v./treatment) and sapofectosid (30 μg s.c. treatment). The treatment was compared to a vehicle (PBS) control and treatment without sapofectosid in terms of body weight, tumor growth and integrated density of tumor luminescence. The study revealed an anti-tumoral effect of the sapofectosid mediated gene therapy in the Neuro-2A-tumor model. The treatments were well tolerated by the animals indicating the applicability of this approach. With these results, we were able to proof the efficacy of a therapy, consisting of targeted suicide gene nanoplexes and sapofectosid, a novel and potent transfection enhancer. This study points out the enormous value for future targeted cancer and gene therapies.

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.

Impact of Mistletoe Triterpene Acids on the Uptake of Mistletoe Lectin by Cultured Tumor Cells.

Complementary treatment possibilities for the therapy of cancer are increasing in demand due to the severe side effects of the standard cytostatics used in the first-line therapy. A common approach as a complementary treatment is the use of aqueous extracts of Viscum album L. (Santalaceace). The therapeutic activity of these extracts is attributed to Mistletoe lectins which are Ribosome-inactivating proteins type II. Besides these main constituents the extract of Viscum album L. comprises also a mixture of lipophilic ingredients like triterpene acids of the oleanane, lupane and ursane type. However, these constituents are not contained in commercially available aqueous extracts due to their high lipophilicity and insolubility in aqueous extraction media. To understand the impact of the extract ingredients in cancer therapy, the intracellular uptake of the mistletoe lectin I (ML) by cultured tumor cells was investigated in relation to the mistletoe triterpene acids, mainly oleanolic acid. Firstly, these hydrophobic triterpene acids were solubilized using cyclodextrins (“TT” extract). Afterwards, the uptake of either single compounds (isolated ML and the aqueous “viscum” extract) or in combination with the TT extract (ML+TT, viscumTT), was analyzed. The uptake of ML was studied inTHP-1-, HL-60-, 143B- and Ewing TC-71-cells and determined after 30, 60 and 120 minutes by an enzyme linked immunosorbent assay which quantifies the A-chain of the hololectin. It could be shown that the intracellular uptake after 120 minutes amounted to 20% in all cell lines after incubation with viscumTT. The studies further revealed that the uptake in THP-1-, HL-60- and Ewing TC-71-cells was independent of the addition of TT extract. Interestingly, the uptake of ML by 143B-cells could only be measured after addition of triterpenes pointing to resistance to mistletoe lectin.

Stacking Interactions mediate Recognition in Ribosome Inactivating Protein

Ribosome Inactivating Proteins (RIPs) are capable of inhibiting protein synthesis by catalytically hydrolyzing at specific purine residues from the sarcin / ricin loop of large ribosomal RNA. There are two types of RIPs: type 1 - RIPs (RIP-1) are single polypeptide chain proteins while type 2 - RIPs contain two polypeptide chains which are covalently linked by a disulphide bond. Studies have indicated that stacking interactions play a dominant role in the ligand binding to RIPs. However, the structural basis of these interactions with RIPs as well as the nature of stack pairing and associated molecular mechanisms are not clearly understood. In order to examine the significance of these stacking interactions and the role of various aromatic residues involved, we have carried out the structural analysis of the complexes of RIP-1 from Momordica balsamina (MbRIP-1) and crystallized it with six different sugar molecules, ribose, fucose, glucose, fructose, maltose and lactose. The crystals belong to hexagonal space group H3 with approximate cell dimension of a = b = 130 Å, c = 40.5 Å. The r.m.s. deviation for the Calpha atoms in the complexed structures was found to be in the range of 0.5 Å to 0.9 Å. The aromatic rings of sugars are seen to be involved in stacking with aromatic rings of Tyr 70 and Tyr 111. The side chain torsion angles chi1 and chi2 of Tyr 70 in the complexes with ribose, fucose, glucose, fructose, maltose and lactose were found to be 64° / 161°, 166° / 86°, 6° / 172°, 70° / 167°, 64° / 161° and -75° / 178° respectively. The sugars are held firmly in the binding site of RIP-1 with the help of stacking interactions and hydrogen bonds. The results presented here have revealed the significance of aromatic stack pairing and delineated the stabilizing role of tyrosine residue in these interactions.

More triterpenoid bisdesmosidic saponins from Agrostemma githago L. (corn cockle)

The common corn cockle (Agrostemma githago L., Caryophyllaceae) is a slender pink originally european wild-flower. Formerly widespread among wheat fields today the plant is nearly eradicated in modern agriculture and has become an endangered species that is protected by law [1]. In the past Agrostemma githago gained notoriety for its toxicity when poisoning people who consumed grain contaminated with the plant seeds [2]. This toxicity is believed to be a conserved defense mechanism based on a synergistic cytotoxicity of the contained saponins and the ribosome-inactivating protein type I (RIP-I) agrostin. Hebestreit et al. could approve this assumption. Both, the saponins as well as the RIP-I did only show little cytotoxicity when applied separately but revealed an increase in the RIP-I cytotoxicity in a synergistic manner when applied in combination in a cell culture model. Moreover Hebestreit et al. found an extraordinary high synergistic cytotoxicity when agrostin was combined with Agrostemma saponins instead of other triterpenoic saponins of similar molecular mass [3]. In 1974 Tschesche et al. and in 1998 Siepmann et al. published the structures of respectively two saponins isolated from Agrostemma githago L. [4, 5]. However other sources claim the isolation of further saponins, the accurate used species are usually not clear. We isolated four bisdesmosidic oleanane-type saponins with masses from 1527.8 g/mol to 1690.8 g/mol which partially enhanced the cytotoxicity of the RIP-I agrostin and saporin.

Structure–activity relationships of saponins enhancing the cytotoxicity of ribosome-inactivating proteins type I (RIP-I)

Saponins are amphiphilic secondary plant compounds able to interfere with surfaces and permeabilize membranes. In addition to antimicrobial and anti-inflammatory features, anti-neoplastic activities are described which base on various mechanisms. A very promising anti-cancer strategy is the synergistic enhancement of the cytotoxicity of ribosome-inactivating proteins type I (RIP-I) by suitable saponins. The cytotoxicity of the naturally low cytotoxic activity showing RIP-I can be augmented up to 100,000-fold, if they are applied in combination with appropriate saponins. These saponins have to hold certain structural features.We analyzed 56 different saponins for their non-synergistic, as well as their synergistic cytotoxicity with the RIP-I saporin from Saponaria officinalis L. (Caryophyllaceae). The saponins were assorted into categories, according to their structural features and their cytotoxic behavior, to build up structure–activity relationships. A non-synergistic cytotoxicity as low as possible and a synergistic cytotoxicity as high as possible were desired.The investigations suggest that ideal saponins consist of an oleanane-type scaffold, preferably gypsogenin or quillaic acid, three branched sugars at the C-3–OH-group including glucuronic acid, galactose, xylose and four branched sugars at the C-28–OH-group, including deoxy-sugars and acetyl-residues.

The investigation of structural requirements for saponins to enable synergistic cytotoxicity with type-I-RIP/lectins

Saponins and lectins, especially the naturally very low cytotoxic activity showing type-I-RIP (ribosome-inactivating proteins type I)/lectins exhibit a synergistic cytotoxicity when applied to cancer cells [1]. The pre-appliance of certain saponins can drastically amplify the cytotoxicity of the type-I-RIP [2, 3] and has become a promising strategy in anti-cancer research [2]. These saponins may also minimize the required effective dose of these very expensive (especially when linked to human antibodies and natural ligands) and time-consuming to purify/to create substances [5].

New results on saponins and saponin-rich plant-extracts enabling synergistic cytotoxicity with type-I-RIPs/lectins

The synergistic cytotoxicity between saponins and lectins, especially the naturally very low cytotoxic activity showing type-I-RIPs (ribosome-inactivating protein type I)/lectins is known for years by now [1]. It has become a promising strategy in anti-cancer research [2]. While the pre-appliance of certain saponins can drastically amplify the cytotoxicity of the type-I-RIPs [3, 4], it may also minimize the required effective dose of these very expensive (especially when linked to human antibodies) and time-consuming to purify/to create substances [5].

Plant ribosome-inactivating proteins type II induce the unfolded protein response in human cancer cells.

Cytotoxic ribosome-inactivating proteins (RIPs) of type II such as ricin were investigated as anti-cancer agents, but also pose a threat as biological weapons. The molecular mechanism leading to their toxic effects is, however, not yet clear. The current paradigm, which states that the irreversible depurination of 28S rRNA results in a general translational arrest eventually leading to cell death, has been questioned. Using micro-array, qRT-PCR and Western blot, we identified the unfolded protein response (UPR), a cellular mechanism activated in response to endoplasmic reticulum stress, that is induced in HCT116 and MDA-MB-231 cells exposed to the plant type II RIPs ricin, riproximin and volkensin. Apoptosis was induced by concentrations at which translation of UPR-related genes still occurred, despite concomitant ribosomal depurination. We conclude that UPR induction represents a model that better describes the cellular effects of RIP exposure at concentrations at which selected proteins are translated despite ribosomal depurination.

Different Functions and Expression Profiles of Curcin and Curcin-L in Jatropha curcas L.

To date, two types of ribosome-inactivating proteins (RIPs) have been found in Jatropha curcas. One is curcin, which has been isolated from the endosperm, and the other is curcin-L, which is expressed in leaves upon stress treatment. Phylogenetic analysis of the predicted amino acid sequences of the RIPs in plants revealed that these belong to a major subfamily and are close to trichosanthin (TCS). Studies on the mRNA and protein levels showed that both curcin and curcin-L have an organ-specific expression pattern. Curcin is only expressed and accumulated in the endosperm; its expression begins in the globular embryo period and peaks during the mature embryo period. In contrast, curcin-L is only expressed in the leaves, but its expression is induced by certain conditions such as treatment with phytohormones or polyethylene glycol, exposure to high and low temperatures, and fungal infection. Analysis of the 5' flanking regions of curcin and curcin-L revealed that the 5' flanking region of curcin-L has three major inserted fragments, which are not present in the corresponding region of curcin. Comparison of characteristic cis-elements suggests the presence of several motifs that are involved in the endosperm-specific expression in the 5' flanking region of curcin, while in curcin-L some stress- and defense-responsive motifs are found to be mainly located in the three inserted fragments. Comparison of the antifungal activity of the two RIPs showed that the one of curcin-L is higher than that of curcin. Differences in the expression and activity of curcin and curcin-L suggest that these two RIPs have different functions.

Comparative Study of the Sensitivity of Lymphoblastoid and Transformed Monocytic Cell Lines to the Cytotoxic Effects of Viscum album Extracts of Different Origin

Viscum album (VA) preparations consist of aqueous extracts of V. album, the European mistletoe. VA extracts contain mistletoe lectins, which are members of the ribosome-inactivating protein type II family. VA preparations have cytotoxic and immunomodulatory properties. Cytotoxicity induced by VA extracts may differ greatly according to the origin of the preparation (host tree, fermented extract) and the cell type. This work was performed to assess the cytotoxicity of various VA preparations, i.e. VA Qu FrF, Qu Spez, M Spez and VA P, in lymphoblastoid and monocytic cell lines. VA Qu FrF, Qu Spez and M Spez induced dose-dependent cell death and inhibition of cell proliferation in lymphoblastoid T cell lines and in transformed monocytic lines. In contrast, the majority of B cell lines tested were resistant to cytotoxicity induced by VA extracts. While VA Qu FrF, Qu Spez and M Spez were potent inducers of cell death, extracts of VA P, derived from mistletoe plants growing on pine trees, failed to induce any cell death in any of the cell lines examined.

Ribosome-Inactivating Proteins: A Family of Plant Proteins That Do More Than Inactivate Ribosomes

ABSTRACT Many plants contain proteins that are commonly designated as ribosome-inactivating proteins (RIPs). Based on the structure of the genes and the mature proteins a novel system is proposed to unambiguously classify all RIPs in type-1, type-2, and type-3 RIPs. In addition, the concept of one- and two-chain type-1 RIPs is introduced. After an overview of the occurrence, molecular structure, and amino acid sequences of RIPs, the formation of the mature proteins from the primary translation products of the corresponding mRNAs is elaborated in detail in a section dealing with the biosynthesis, posttranslational modifications, topogenesis, and subcellular location of the different types of RIPs. Details about the three-dimensional structure of type-1 RIPs and the A and B chains of type-2 RIPs are discussed in a separate section. Based on the data given in the previous sections, the phylogenic and molecular evolution of RIPs is critically assessed and a novel model is proposed for the molecular evolution of RIPs. Subsequently, the enzymatic activities of RIPs are critically discussed whereby special attention is given to some presumed novel activities, and a brief overview is given of the biological activities of the different types of RIPs on cells and whole organisms. By combining the data on the enzymatic activities and biological activities of RIPs, and the current knowledge of different plant physiological aspects of these proteins, the role of RIPs in plants is revisited. Thereby the attention is focussed on the role of RIPs in plant defense with the emphasis on protection against plant-eating organisms and viruses. Finally, there is a short discussion on the discovery of a novel class of enzymes called RALyases that use ribosomes damaged by RIPs as a substrate and may act cooperatively with RIPs. There is discussion regarding why the identification of this novel enzyme gives valuable clues to the origin and original function of RIPs and may be helpful to unravel the physiological role of modem RIPs.

Ribosome-Inactivating Proteins: A Family of Plant Proteins That Do More Than Inactivate Ribosomes

ABSTRACT Many plants contain proteins that are commonly designated as ribosome-inactivating proteins (RIPs). Based on the structure of the genes and the mature proteins a novel system is proposed to unambiguously classify all RIPs in type-1, type-2, and type-3 RIPs. In addition, the concept of one- and two-chain type-1 RIPs is introduced. After an overview of the occurrence, molecular structure, and amino acid sequences of RIPs, the formation of the mature proteins from the primary translation products of the corresponding mRNAs is elaborated in detail in a section dealing with the biosynthesis, posttranslational modifications, topogenesis, and subcellular location of the different types of RIPs. Details about the three-dimensional structure of type-1 RIPs and the A and B chains of type-2 RIPs are discussed in a separate section. Based on the data given in the previous sections, the phylogenic and molecular evolution of RIPs is critically assessed and a novel model is proposed for the molecular evolution of RIPs. Subsequently, the enzymatic activities of RIPs are critically discussed whereby special attention is given to some presumed novel activities, and a brief overview is given of the biological activities of the different types of RIPs on cells and whole organisms. By combining the data on the enzymatic activities and biological activities of RIPs, and the current knowledge of different plant physiological aspects of these proteins, the role of RIPs in plants is revisited. Thereby the attention is focussed on the role of RIPs in plant defense with the emphasis on protection against plant-eating organisms and viruses. Finally, there is a short discussion on the discovery of a novel class of enzymes called RALyases that use ribosomes damaged by RIPs as a substrate and may act cooperatively with RIPs. There is discussion regarding why the identification of this novel enzyme gives valuable clues to the origin and original function of RIPs and may be helpful to unravel the physiological role of modem RIPs.

Pokeweed antiviral protein and its applications.

The genus Phytolacca produces a number of proteins that have antiviral properties. These antiviral proteins are ribosome-inactivating proteins (RIPs) which remove a single adenine from a highly conserved, surface-exposed, stem-loop structure in the large rRNA of eukaryotic and prokaryotic ribosomes. They are found in two general forms: dimeric toxins (type II) containing a cell binding protein linked to the RIP by a disulfide bond, and single chain RIPs (type I), such as those found in pokeweed, composed of a single chain. A number of single-chain RIPs have been isolated from leaves, seeds and roots of a wide variety of plants (for reviews see Irvin and Uckun 1992; Irvin 1995).KeywordsTransgenic PlantAntiviral ActivitySalicylic Acid LevelAntiviral ProteinTobacco Mosaic Virus InfectionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Simultaneous existence of two types of ribosome-inactivating proteins in the seeds of Cinnamonum camphora — characterization of the enzymatic activities of these cytotoxic proteins

Two types of ribosome-inactivating proteins (RIPs), camphorin and cinnamomin, have been purified from the seeds of Cinnamomum camphora. Camphorin is a type I RIP with a molecular mass of 23 kDa. Cinnamomin is a type II RIP having three isoforms, its molecular mass is around 61 kDa. The A- and B-chain derived from cinnamomin isoforms have similar mobilities in SDS-polyacrylamide gel. Camphorin and cinnamomin are both glycoproteins. In phylogenesis, it is particularly significant to find the simultaneous existence of type I and type II RIP as well as three isoforms of the latter in the same organ of a higher plant. The molecular mechanism of action of these two RIPs on mammalian ribosomes was demonstrated to be the specific RNA N-glycosidase activity. They modify 28S RNA among the four species of ribosomal RNAs. The cleavage site is the adenosine at position 4324 (rat liver 28S rRNA) embedded in the highly conserved ‘R/S domain’. It is the first report that an intact type II RIP (cinnamomin) exhibits RNA N-glycosidase activity. Additionally, camphorin and cinnamomin can cleave supercoiled double-stranded DNA into nicked and linear forms (Ling et al. (1994) FEBS Lett. 345, 143–146).