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Toxins
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Biological Activities of Ribosome-Inactivating Proteins
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Biological Activities of Ribosome-Inactivating Proteins

A special issue of Toxins (ISSN 2072-6651).

Deadline for manuscript submissions: closed (31 July 2022) | Viewed by 35608

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Prof. Dr. José Miguel Ferreras

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Guest Editor
Department of Biochemistry, Molecular Biology and Physiology, Faculty of Sciences, University of Valladolid, E-47011 Valladolid, Spain
Interests: ribosome-inactivating proteins (RIPs); immunotoxins; protein synthesis inhibition; ribotoxins; structure–activity relationship
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Lucía Citores

E-Mail Website1 Website2
Guest Editor
Department of Biochemistry, Molecular Biology and Physiology, Faculty of Sciences, University of Valladolid, E-47011 Valladolid, Spain
Interests: ribosome-inactivating proteins (RIPs); immunotoxins; protein synthesis inhibition; ribotoxins; protein translocation; intracellular transport; apoptosis
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Ribosome-inactivating proteins (RIPs) are rRNA N-glycosylases (EC 3.2.2.22) isolated mainly from plants and some bacteria that specifically catalyze the hydrolysis of the second N-glycosidic bond from the GAGA tetraloop located in the Sarcin Ricin Loop (SRL) of the large ribosomal RNA. Because the SRL is crucial for anchoring the elongation factors on the ribosome, depurination causes the irreversible inactivation of ribosomes. In addition, RIPs usually display other enzymatic activities, being the most relevant their polynucleotide:adenosine glycosylase activity on all kinds of nucleic acids. RIPs have been classified into two types depending on the presence (type 2 RIPs) or the absence (type 1 RIPs) of a lectin chain (B chain). The presence of the B chain may turn type 2 RIPs into powerful toxins, such as ricin or abrin. Regardless, despite the absence of the B chain, type 1 RIPs, at higher concentrations, are also able to enter into cells and display toxicity to cells and animals.

The exact biological role that RIPs play remains unknown, but it is thought to represent a defense mechanism of a plant against pathogens and predators.

As a consequence of their enzymatic action, RIPs display several biological activities, including antiviral, antibacterial, antifungal, antifeedant, and antiproliferative activities, which may be relevant to their functions and biotechnological applications.

The most promising applications of RIPs in experimental medicine, especially in anticancer therapy, are related to their use as a component of immunotoxins, in which the RIP is linked to antibodies that mediate their binding and internalization by malignant cells. In agriculture, RIPs have been shown to increase resistance against viruses, fungi, and insects in transgenic plants.

The focus of this Special Issue of Toxins will be on the biological activities of RIPs that may be relevant to their biological functions and biotechnological applications, as well as on the elucidation of the structure-activity relationships of these proteins.

Prof. Dr. José Miguel Ferreras
Prof. Dr. Lucía Citores
Guest Editors

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Keywords

  • antifeedant
  • antifungal
  • antitumoral
  • antiviral
  • apoptosis
  • immunotoxin
  • ribosome-inactivating protein (RIP)
  • rRNA N-glycosylase

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Related Special Issue

Published Papers (11 papers)

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Editorial

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4 pages, 223 KiB  
Editorial
Biological Activities of Ribosome-Inactivating Proteins
by Lucía Citores and José M. Ferreras
Toxins 2023, 15(1), 35; https://doi.org/10.3390/toxins15010035 - 1 Jan 2023
Cited by 6 | Viewed by 1881
Abstract
After more than 50 years of research, studies on the structure and biological activities of ribosome-inactivating proteins (RIPs) continue to provide a field of great interest within the scientific community, both for the health risks they pose and their applications in medicine and [...] Read more.
After more than 50 years of research, studies on the structure and biological activities of ribosome-inactivating proteins (RIPs) continue to provide a field of great interest within the scientific community, both for the health risks they pose and their applications in medicine and biotechnology [...] Full article
(This article belongs to the Special Issue Biological Activities of Ribosome-Inactivating Proteins)

Research

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14 pages, 2299 KiB  
Article
LRP1-Mediated Endocytosis May Be the Main Reason for the Difference in Cytotoxicity of Curcin and Curcin C on U2OS Osteosarcoma Cells
by Siying Qin, Xueying Wang, Pan Han, Zhiping Lai, Yingying Ren, Rui Ma, Cheng Cheng, Ting Wang and Ying Xu
Toxins 2022, 14(11), 771; https://doi.org/10.3390/toxins14110771 - 8 Nov 2022
Cited by 3 | Viewed by 2693
Abstract
Curcin and Curcin C, both of the ribosome-inactivating proteins of Jatropha curcas, have apparent inhibitory effects on the proliferation of osteosarcoma cell line U20S. However, the inhibitory effect of the latter is 13-fold higher than that of Curcin. The mechanism responsible for [...] Read more.
Curcin and Curcin C, both of the ribosome-inactivating proteins of Jatropha curcas, have apparent inhibitory effects on the proliferation of osteosarcoma cell line U20S. However, the inhibitory effect of the latter is 13-fold higher than that of Curcin. The mechanism responsible for the difference has not been studied. This work aimed to understand and verify whether there are differences in entry efficiency and pathway between them using specific endocytosis inhibitors, gene silencing, and labeling techniques such as fluorescein isothiocyanate (FITC) labeling. The study found that the internalization efficiency of Curcin C was twice that of Curcin for U2OS cells. More than one entering pathway was adopted by both of them. Curcin C can enter U2OS cells through clathrin-dependent endocytosis and macropinocytosis, but clathrin-dependent endocytosis was not an option for Curcin. The low-density lipoprotein receptor-related protein 1 (LRP1) was found to mediate clathrin-dependent endocytosis of Curcin C. After LRP1 silencing, there was no significant difference in the 50% inhibitory concentration (IC50) and endocytosis efficiency between Curcin and Curcin C on U2OS cells. These results indicate that LRP1-mediated endocytosis is specific to Curcin C, thus leading to higher U2OS endocytosis efficiency and cytotoxicity than Curcin. Full article
(This article belongs to the Special Issue Biological Activities of Ribosome-Inactivating Proteins)
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14 pages, 3323 KiB  
Article
Characterization of Lung Injury following Abrin Pulmonary Intoxication in Mice: Comparison to Ricin Poisoning
by Anita Sapoznikov, Yoav Gal, Ron Alcalay, Yentl Evgy, Tamar Sabo, Chanoch Kronman and Reut Falach
Toxins 2022, 14(9), 614; https://doi.org/10.3390/toxins14090614 - 2 Sep 2022
Cited by 3 | Viewed by 1919
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Biological Activities of Ribosome-Inactivating Proteins)
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29 pages, 3103 KiB  
Article
Structure and Biological Properties of Ribosome-Inactivating Proteins and Lectins from Elder (Sambucus nigra L.) Leaves
by Rosario Iglesias, Rosita Russo, Nicola Landi, Mariangela Valletta, Angela Chambery, Antimo Di Maro, Andrea Bolognesi, José M. Ferreras and Lucía Citores
Toxins 2022, 14(9), 611; https://doi.org/10.3390/toxins14090611 - 1 Sep 2022
Cited by 7 | Viewed by 2942
Abstract
Ribosome-inactivating proteins (RIPs) are a group of proteins with rRNA N-glycosylase activity that catalyze the removal of a specific adenine located in the sarcin–ricin loop of the large ribosomal RNA, which leads to the irreversible inhibition of protein synthesis and, consequently, cell death. [...] Read more.
Ribosome-inactivating proteins (RIPs) are a group of proteins with rRNA N-glycosylase activity that catalyze the removal of a specific adenine located in the sarcin–ricin loop of the large ribosomal RNA, which leads to the irreversible inhibition of protein synthesis and, consequently, cell death. The case of elderberry (Sambucus nigra L.) is unique, since more than 20 RIPs and related lectins have been isolated and characterized from the flowers, seeds, fruits, and bark of this plant. However, these kinds of proteins have never been isolated from elderberry leaves. In this work, we have purified RIPs and lectins from the leaves of this shrub, studying their main physicochemical characteristics, sequences, and biological properties. In elderberry leaves, we found one type 2 RIP and two related lectins that are specific for galactose, four type 2 RIPs that fail to agglutinate erythrocytes, and one type 1 RIP. Several of these proteins are homologous to others found elsewhere in the plant. The diversity of RIPs and lectins in the different elderberry tissues, and the different biological activities of these proteins, which have a high degree of homology with each other, constitute an excellent source of proteins that are of great interest in diagnostics, experimental therapy, and agriculture. Full article
(This article belongs to the Special Issue Biological Activities of Ribosome-Inactivating Proteins)
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16 pages, 3023 KiB  
Article
Isolation, Characterization and Biological Action of Type-1 Ribosome-Inactivating Proteins from Tissues of Salsola soda L.
by Nicola Landi, Sara Ragucci, Lucía Citores, Angela Clemente, Hafiza Z. F. Hussain, Rosario Iglesias, José M. Ferreras and Antimo Di Maro
Toxins 2022, 14(8), 566; https://doi.org/10.3390/toxins14080566 - 19 Aug 2022
Cited by 12 | Viewed by 2738
Abstract
Ribosome-inactivating proteins (RIPs) are known as RNA N-glycosylases. They depurinate the major rRNA, damaging ribosomes and inhibiting protein synthesis. Here, new single-chain (type-1) RIPs named sodins were isolated from the seeds (five proteins), edible leaves (one protein) and roots (one protein) of Salsola [...] Read more.
Ribosome-inactivating proteins (RIPs) are known as RNA N-glycosylases. They depurinate the major rRNA, damaging ribosomes and inhibiting protein synthesis. Here, new single-chain (type-1) RIPs named sodins were isolated from the seeds (five proteins), edible leaves (one protein) and roots (one protein) of Salsola soda L. Sodins are able to release Endo’s fragment when incubated with rabbit and yeast ribosomes and inhibit protein synthesis in cell-free systems (IC50 = 4.83–79.31 pM). In addition, sodin 5, the major form isolated from seeds, as well as sodin eL and sodin R, isolated from edible leaves and roots, respectively, display polynucleotide:adenosine glycosylase activity and are cytotoxic towards the Hela and COLO 320 cell lines (IC50 = 0.41–1200 nM), inducing apoptosis. The further characterization of sodin 5 reveals that this enzyme shows a secondary structure similar to other type-1 RIPs and a higher melting temperature (Tm = 76.03 ± 0.30 °C) and is non-glycosylated, as other sodins are. Finally, we proved that sodin 5 possesses antifungal activity against Penicillium digitatum. Full article
(This article belongs to the Special Issue Biological Activities of Ribosome-Inactivating Proteins)
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17 pages, 2961 KiB  
Article
Sapovaccarin-S1 and -S2, Two Type I RIP Isoforms from the Seeds of Saponaria vaccaria L.
by Louisa Schlaak, Christoph Weise, Benno Kuropka and Alexander Weng
Toxins 2022, 14(7), 449; https://doi.org/10.3390/toxins14070449 - 30 Jun 2022
Cited by 3 | Viewed by 2144
Abstract
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, [...] Read more.
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. Full article
(This article belongs to the Special Issue Biological Activities of Ribosome-Inactivating Proteins)
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15 pages, 2915 KiB  
Article
Ebulin l Is Internalized in Cells by Both Clathrin-Dependent and -Independent Mechanisms and Does Not Require Clathrin or Dynamin for Intoxication
by Rosario Iglesias, José M. Ferreras, Alicia Llorente and Lucía Citores
Toxins 2021, 13(2), 102; https://doi.org/10.3390/toxins13020102 - 30 Jan 2021
Cited by 3 | Viewed by 2316
Abstract
Ebulin l is an A-B toxin, and despite the presence of a B chain, this toxin displays much less toxicity to cells than the potent A-B toxin ricin. Here, we studied the binding, mechanisms of endocytosis, and intracellular pathway followed by ebulin l [...] Read more.
Ebulin l is an A-B toxin, and despite the presence of a B chain, this toxin displays much less toxicity to cells than the potent A-B toxin ricin. Here, we studied the binding, mechanisms of endocytosis, and intracellular pathway followed by ebulin l and compared it with ricin. COS-1 cells and HeLa cells with inducible synthesis of a mutant dynamin (K44A) were used in this study. The transport of these toxins was measured using radioactively or fluorescently labeled toxins. The data show that ebulin l binds to cells to a lesser extent than ricin. Moreover, the expression of mutant dynamin does not affect the endocytosis, degradation, or toxicity of ebulin l. However, the inhibition of clathrin-coated pit formation by acidification of the cytosol reduced ebulin l endocytosis but not toxicity. Remarkably, unlike ricin, ebulin l is not transported through the Golgi apparatus to intoxicate the cells and ebulin l induces apoptosis as the predominant cell death mechanism. Therefore, after binding to cells, ebulin l is taken up by clathrin-dependent and -independent endocytosis into the endosomal/lysosomal system, but there is no apparent role for clathrin and dynamin in productive intracellular routing leading to intoxication. Full article
(This article belongs to the Special Issue Biological Activities of Ribosome-Inactivating Proteins)
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18 pages, 11777 KiB  
Article
Kirkiin: A New Toxic Type 2 Ribosome-Inactivating Protein from the Caudex of Adenia kirkii
by Massimo Bortolotti, Stefania Maiello, José M. Ferreras, Rosario Iglesias, Letizia Polito and Andrea Bolognesi
Toxins 2021, 13(2), 81; https://doi.org/10.3390/toxins13020081 - 22 Jan 2021
Cited by 11 | Viewed by 3235
Abstract
Ribosome-inactivating proteins (RIPs) are plant toxins that irreversibly damage ribosomes and other substrates, thus causing cell death. RIPs are classified in type 1 RIPs, single-chain enzymatic proteins, and type 2 RIPs, consisting of active A chains, similar to type 1 RIPs, linked to [...] Read more.
Ribosome-inactivating proteins (RIPs) are plant toxins that irreversibly damage ribosomes and other substrates, thus causing cell death. RIPs are classified in type 1 RIPs, single-chain enzymatic proteins, and type 2 RIPs, consisting of active A chains, similar to type 1 RIPs, linked to lectin B chains, which enable the rapid internalization of the toxin into the cell. For this reason, many type 2 RIPs are very cytotoxic, ricin, volkensin and stenodactylin being the most toxic ones. From the caudex of Adenia kirkii (Mast.) Engl., a new type 2 RIP, named kirkiin, was purified by affinity chromatography on acid-treated Sepharose CL-6B and gel filtration. The lectin, with molecular weight of about 58 kDa, agglutinated erythrocytes and inhibited protein synthesis in a cell-free system at very low concentrations. Moreover, kirkiin was able to depurinate mammalian and yeast ribosomes, but it showed little or no activity on other nucleotide substrates. In neuroblastoma cells, kirkiin inhibited protein synthesis and induced apoptosis at doses in the pM range. The biological characteristics of kirkiin make this protein a potential candidate for several experimental pharmacological applications both alone for local treatments and as component of immunoconjugates for systemic targeting in neurodegenerative studies and cancer therapy. Full article
(This article belongs to the Special Issue Biological Activities of Ribosome-Inactivating Proteins)
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13 pages, 2370 KiB  
Article
Antiviral Activity of PD-L1 and PD-L4, Type 1 Ribosome Inactivating Proteins from Leaves of Phytolacca dioica L. in the Pathosystem Phaseolus vulgaris–Tobacco Necrosis Virus (TNV)
by Daniela Bulgari, Nicola Landi, Sara Ragucci, Franco Faoro and Antimo Di Maro
Toxins 2020, 12(8), 524; https://doi.org/10.3390/toxins12080524 - 14 Aug 2020
Cited by 8 | Viewed by 3160
Abstract
Using the pathosystem Phaseolus vulgaris–tobacco necrosis virus (TNV), we demonstrated that PD-L1 and PD-L4, type-1 ribosome inactivating proteins (RIPs) from leaves of Phytolacca dioica L., possess a strong antiviral activity. This activity was exerted both when the RIPs and the virus were [...] Read more.
Using the pathosystem Phaseolus vulgaris–tobacco necrosis virus (TNV), we demonstrated that PD-L1 and PD-L4, type-1 ribosome inactivating proteins (RIPs) from leaves of Phytolacca dioica L., possess a strong antiviral activity. This activity was exerted both when the RIPs and the virus were inoculated together in the same leaf and when they were inoculated or applied separately in the adaxial and abaxial leaf surfaces. This suggests that virus inhibition would mainly occur inside plant cells at the onset of infection. Histochemical studies showed that both PD-L1 and PD-L4 were not able to induce oxidative burst and cell death in treated leaves, which were instead elicited by inoculation of the virus alone. Furthermore, when RIPs and TNV were inoculated together, no sign of H2O2 deposits and cell death were detectable, indicating that the virus could have been inactivated in a very early stage of infection, before the elicitation of a hypersensitivity reaction. In conclusion, the strong antiviral activity is likely exerted inside host cells as soon the virus disassembles to start translation of the viral genome. This activity is likely directed towards both viral and ribosomal RNA, explaining the almost complete abolition of infection when virus and RIP enter together into the cells. Full article
(This article belongs to the Special Issue Biological Activities of Ribosome-Inactivating Proteins)
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Review

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23 pages, 727 KiB  
Review
Antiviral Activity of Ribosome-Inactivating Proteins
by Lucía Citores, Rosario Iglesias and José M. Ferreras
Toxins 2021, 13(2), 80; https://doi.org/10.3390/toxins13020080 - 22 Jan 2021
Cited by 45 | Viewed by 5875
Abstract
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Biological Activities of Ribosome-Inactivating Proteins)
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18 pages, 1335 KiB  
Review
Engineering of Ribosome-inactivating Proteins for Improving Pharmacological Properties
by Jia-Qi Lu, Zhen-Ning Zhu, Yong-Tang Zheng and Pang-Chui Shaw
Toxins 2020, 12(3), 167; https://doi.org/10.3390/toxins12030167 - 9 Mar 2020
Cited by 23 | Viewed by 4884
Abstract
Ribosome-inactivating proteins (RIPs) are N-glycosidases, which depurinate a specific adenine residue in the conserved α-sarcin/ricin loop (α-SRL) of rRNA. This loop is important for anchoring elongation factor (EF-G for prokaryote or eEF2 for eukaryote) in mRNA translocation. Translation is inhibited after the attack. [...] Read more.
Ribosome-inactivating proteins (RIPs) are N-glycosidases, which depurinate a specific adenine residue in the conserved α-sarcin/ricin loop (α-SRL) of rRNA. This loop is important for anchoring elongation factor (EF-G for prokaryote or eEF2 for eukaryote) in mRNA translocation. Translation is inhibited after the attack. RIPs therefore may have been applied for anti-cancer, and anti-virus and other therapeutic applications. The main obstacles of treatment with RIPs include short plasma half-life, non-selective cytotoxicity and antigenicity. This review focuses on the strategies used to improve the pharmacological properties of RIPs on human immunodeficiency virus (HIV) and cancers. Coupling with polyethylene glycol (PEG) increases plasma time and reduces antigenicity. RIPs conjugated with antibodies to form immunotoxins increase the selective toxicity to target cells. The prospects for future development on the engineering of RIPs for improving their pharmacological properties are also discussed. Full article
(This article belongs to the Special Issue Biological Activities of Ribosome-Inactivating Proteins)
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