Ricin protein synthesis inhibition

Montesano, L., Cawley, D., and Herschman, H.R. (1982) Disuccinimidyl suberate cross-linked ricin does not inhibit cell-free protein synthesis. Biochem. Biophys. Res. Comm. 109, 7-13. 

Delayed-action cytotoxin that inhibits protein synthesis (ribosomal inactivating protein) that is obtained from castor beans (Ricinus communis). Waste from production of castor oil contains about 5% ricin by weight. It is a white powder that is soluble in water and relatively heat stable. Aqueous solutions are resistant to chlorine at 10 ppm. It is persistent in the environment. 

Caution Ricin is extremely toxic to cells and acts by inhibiting protein synthesis. After aerosol exposure, signs and symptoms would depend on the dose inhaled. Humans can be expected to develop severe lung inflammation with progressive cough, dyspnea, cyanosis, and pulmonary edema. 

Ricin is a potent cellular protein toxin contained in the beans of the castor been plant (Ricinus communis), which is extensively cultivated for oil production and is also a common ornamental garden plant. Ricin is able to inhibit ribosomal protein synthesis eventually causing cell death, and owing to these properties it has been allegedly used in terrorist and criminal activities. After trypsin digestion of castor bean crude extracts, Ostin et al. [105] were able to unambiguously... 

Highly potent bacterial toxins such as ricin and diphtheria can completely inhibit cellular protein synthesis at very low levels [26]. The bacterial toxin exerts cytotoxicity through enzymatic inactivation of factors essential for protein synthesis (e.g., riboso-mal RNA, elongation factor 2 or EF2). Inactivation of these proteins, which are... 

RIPs are plant protein toxins that are able to inhibit enzymatically ribosomal activity and are therefore highly cytotoxic [98]. RIPs are taken up in the cells by means of endocytosis, and only a small fraction (5% or less) are translocated to the cytosol where the toxins inhibit the protein synthesis and eventually kill the cell. PCI may be used to increase both the efficacy and specificity of these toxins. RIPs are divided into two groups, type I and type II. Type II RIPs, like ricin, consists of two polypeptide chains, one cytotoxic A-chain with /V-glycosidase activity and one B-chain which binds to the cell surface. Type I RIPs, like gelonin, agrostin, and saporin, lack the B chain, which make them poorly transported over the cell- and intracellular membranes to the cell cytosol. Hence, the cytotoxic effect of these protein toxins is usually absent or very low. A considerable cytotoxic effect of type I RIPs has been shown in combination with PCI, both in vitro and in vivo [25, 99]. 

Ricin is extremely toxic to eukaryotic cells.32,150,194,642,844,646,647,649,657 The experiments of Olsnes and Pihl150,639,649 and Pappenheimer and coworkers658 demonstrated that one of the two subunits binds to the cell membrane, presumably by way of a carbohydrate structure, whereas the second subunit inhibits protein synthesis by a catalytic mechanism in a cell-free system. This suggests that toxicity may result from the... 

Abrin exerts its toxic action in the same way as ricin. The abrin B-chain avidly binds to a variety of cell types, in particular reticuloendothehal cells which bear the appropriate mannose receptors. The abrin B-chain also binds to the galactosyl-terminated receptors on the cell membrane to allow the entry of the abrin A-chain. Once internalized, the abrin A-chain is transported from the cell membrane to the ribosomes, where it catalytically inactivates the 60S ribosomal subunit by removing adenine from positions 4 and 324 of 28S rRNA, thereby inhibiting protein synthesis and causing cell death (Stripe and Barbieri, 1986). 

Skilleter, D.N., Paine, A.J., Stirpe, F. (1981). A comparison of the accumulation of ricin by hepatic parenchymal and nonparenchymal cells and its inhibition of protein synthesis. Bio-chim. Biophys. Acta 677 495-500. 

DOT CLASSIFICATION 9 Label None SAFETY PROFILE Deadly poison by ingestion in humans. The seeds contain the deadly poison ricin, a plant lectin (toxalbumin) which inhibits protein synthesis in the intestinal wall. Ingestion of the seeds can cause after a delay period of several hours nausea, vomiting, diarrhea, and intestinal dysfunction. There may be massive fluid and electrolyte loss. Ingestion of as few as 2 seeds could be fatal. A potent allergen. When heated to decomposition it emits toxic fumes of NOx. See also RICIN. 

The glycoproteins (ricin) are poorly absorbed from the gastrointestinal tract however, once absorbed, they most likely follow a distribution pattern similar to that of albumin. Many cell surfaces contain receptors specific for the ricin molecules. This molecule consists of two subunits, A and B, bound by a disulfide link. When this link is broken, the B subunit binds to galactose-containing receptors in the cell wall and is transported intracellularly. The A subunit inhibits protein synthesis. The liver, spleen, adrenal cortex, and bone marrow are the primary sites of distribution. The biotransformation and elimination of toxalbumins are poorly understood. The elimination half-life in one patient was 2 days. The reported disappearance of ricin from the plasma is according to first-order kinetics when... 

Viscum contain lectins that are cytotoxic by inhibiting protein synthesis on the ribosomal level in a manner similar to the toxalbumins ricin and abrin. Viscotoxin and phoratoxin are cardiac toxins and vasoconstrictors. Both produced reflex bradycardia, negative inotropic effects, and, in high doses, vasoconstriction of skin and skeletal muscle vessels in animals. 

How does toxalbumin relate to ricin Toxalbumins consist of two subunits (A and B) which are joined by a disulfide bond. The A subunit irreversibly binds the 60S ribosomal subunit, which blocks protein synthesis. The B subunit allows for binding and penetration across the gastrointestinal cell wall. Sufficient doses of ricin can cause cell death due to continued inhibition of protein synthesis. 

Shiga toxin produced by Shigella dysenteriae has similar structural features. The toxin binds to a glycolipid (Gb3), undergoes endocytosis, and the enzymatie Ai fragment, which is a specific N-glycosidase, removes adenine from one particular adenosine residue in the 28S RNA of the 60S ribosomal subunit. Removal of the adenine inactivates the 60S ribosome, blocking protein synthesis. Ricin, abrin, and a number of related plant proteins inhibit eukaryotic protein synthesis in a similar manner (Chapter 25). 

A group of plant lectins, such as abrin, ricin, and mod-eccin, are highly toxic to eukaryotic cells. Their mode of action consists of inhibition of protein synthesis by enzymatically inactivating the EF-2 binding region of the 60S ribosomal subunit, whereas the diphtheria toxin inactivates the EF-2 protein itself. Ricin is isolated from castor beans and has a molecular weight of 66,000. Like most plant and bacterial toxic proteins, ricin contains two... 

Ricin Is an N-Glycosidase That Inhibits Protein Synthesis... 

Ricin is a biomolecule frequently in the news because of its potential use as a bioterrorism agent. Ricin is a small protein (65 kd) found in the seeds of the castor oil plant, Riemus communis. It is indeed a deadly molecule, because as little as 500 xg is lethal to an adult human, and a single molecule can inhibit all protein synthesis in a cell, resulting in cell death. 

Many clinically important antibiotics function by inhibiting protein synthesis. All steps of protein synthesis are susceptible to inhibition by one antibiotic or another. Diphtheria toxin inhibits protein synthesis by covalently modifying an elongation factor, thereby preventing elongation. Ricin, a toxin from castor beans, inhibits elongation by removing a crucial adenine from rRNA. 

Da. The toxins are made up of two polypeptide chains (A and B) connected by a disulfide bond. The cytotoxicity of ricin is due to inhibition of protein synthesis, caused when the B chain binds to cell-surface receptors and the toxin-receptor complex is taken into the cell, and the A chain that has endonuclease activity and, at extremely low concentrations, will inhibit DNA replication and protein synthesis (USAMRICD, 2005). Ricin is stable under ambient conditions and can be detoxified by heat at 80°C for 10 min, or 50°C for an hour at a pH of 7.8. Chlorine inactivates over 99.4% by 100 mg/L FAC in 20 min. Low chlorine concentrations, such as 10 mg/L FAC, as well as iodine at up to 16 mg/L will have no effect on ricin (USAMRICD, 2005). 

Complete elucidation of the mechanisms by which ricin kills target cells remains an area of active study, but it is clear that the A -glycosidase activity of RTA is the essential triggering event. Inhibition of protein synthesis precedes other detectable alterations in target cell biochemistry. Ricin blocks amino acid incorporation in cmde microsome preparations before changes occur in energy metabohsm or oxidative phosphorylation the toxin has essentially no effect on mitochondrial respiration in isolated mitochondria or tumor cells (Waller et al., 1966 Dirheimer et al., 1968 Lin et al., 1971). Likewise, the first observable cytotoxic effect of ricin in cell culture is typically the inhibition of protein synthesis, followed by a reduction in DNA synthesis (Lin et al., 1970 Lin et al., 1971 Onozaki et al., 1972 Refsnes et al., 1974 Nicolson et al., 1975 Olsnes et al., 1976 Refsnes et al., 1977). 

After addition of ricin, abrin, or modeccin to cell culture medium in vitro, there is a characteristic time delay before the inhibition of protein synthesis becomes apparent the lag time decreases with increasing toxin concentration, but even at high concentrations it is as long as 20-30 min (Refsnes et al., 1974 Olsnes et al., 1976). The cause of this time delay is unknown, but it may partly reflect the complex intracellular trafficking of the toxins. 

Different cell types exhibit different sensitivities to ricin in vitro. For example, the concentration of ricin in tissue culture medium that leads to an approximately 50% inhibition of protein synthesis is 13-22 pM for human lymphoma (Daudi cells), AKR/A, lipopolysaccharide blasts, or mice spleen cells, but it is 0.4 pM for nonparenchymal rat liver cells (Fulton et al., 1986). Ricin causes cytotoxicity in cultured human HeLa cells at concentrations as low as 15 pM (Eiklid et al., 1980 Rao et al., 2005), with an approximately 50% loss of viable cells occurring after a 12 h exposure to... 

Ricin may inhibit the synthesis of specific proteins to different extents in a myeloma cell line, for example, the synthesis of IgA is inhibited more rapidly than is bulk protein synthesis (Ko and Kaji, 1975). There is currently insufficient experimental evidence, however, to conclude that preferential inhibition of the synthesis of specific proteins significantly influences ricin cytotoxicity in vivo. 

It is generally accepted that ricin-induced apoptosis requires RTA, and is a downstream consequence of the inhibition of protein synthesis (Williams et al., 1997 Langer et al., 1999 Oda et al., 1999 Vervecken et al., 2000). There is recent evidence, however, to suggest that apoptosis in yeast cells exposed to ricin may require more than RTA catalytic activity, perhaps involving the subcellullar trafficking of the toxin (Tamura et al., 2002a Li et al., 2006). 

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