Ricin plant toxins

Olsnes, S., and Pihl, A. (1976) Abrin, ricin, and their associated agglutinins. In The Specificity of Animal, Bacterial and Plant Toxins. Receptors and Recognition (P. Cuatrecasas, ed.), Series B, Vol. 1, pp. 129-173. Chapman Hall, London. 

C. botulinum toxins belong to the AB group of toxins, which also includes diphtheria toxin, pseudomonas exotoxin A, anthrax toxin, Shiga(like) toxin, cholera toxin, pertussis toxin, and plant toxins, e.g., ricin. Moiety A has an enzymatic activity and usually modified cellular-target entering cytosol. Moiety B consists of one or more components and binds the toxin to surface receptors, and is responsible for translocation of the A component into cells. AB toxins are produced in a non-active form and are activated by a split between two cysteine residues within a region (Falnes and Sandvig, 2000). 

Ricin is the deadliest plant toxin known. It also has the advantage of being impossible to detect at an autopsy. (Note - Work is currently being done at the University of Leeds in England to develop a means of... 

A major application of LC/ESI/MS is the characterization and detection of toxins, ranging from relatively small molecules, such as mycotoxins and some marine toxins, to the large proteinaceous toxins such as ricin and botulinum toxins. The marine toxin saxitoxin and the plant toxin ricin are specifically listed in Schedule 1 of the CWC as examples of toxins. A comprehensive review of LC/MS in toxin analysis would require a major chapter in its own right. Hancock and D Agostino 1711 reviewed approaches to the mass spectrometric identification of selected low molecular mass toxins. This chapter will describe examples of LC/MS in the analysis of marine, fungal, bacterial, and plant toxins, which are of possible relevance to the CWC. 

Diphtheria toxin is produced as a single polypeptide chain (Fig. la) yyhich is easily cleaved ("nicked") by trypsin and trypsin-like proteases into two disulfide-linked fragments, A and B (Pappenheimer, 1977). The structure of the nicked toxin resembles that of the plant toxins ricin, abrin, modeccin, viscumin and others (Olsnes and Sandvig, 1985). 

Selected Review Articles for Ricin and Related Plant Toxins Title or Topic Area... 

Ricin and related type 2 RIP plant toxins are comparably lethal to laboratory mice under controlled conditions (Table 17.3). Variations in the LD50 values for a single toxin reported by different laboratories are comparable with variations among different toxins. Few controlled animal studies are available for several of these toxins, and comparisons among laboratories are limited by differences in toxin preparations, animal strains, and methodologies employed. The postexposure observation period is a particularly important variable for example, the literature values for the acute toxicity of abrin vary by 80-fold depending on whether intoxicated animals are observed for 24 or 48 h after exposure (Dickers et al., 2003). 

There are likely differences among species in susceptibility to related plant toxins but, as with ricin, these are often obscured by interlaboratory variability. In one comparative study of abrin (i.v.) lethality in different animals, the MED for mice was 10-fold greater (0.7 pg/kg) than that for rabbits (0.03-0.06 pg/kg), with rats and guinea pigs showing intermediate sensitivity (Fodstad et al., 1979) these findings parallel those for ricin (Table 17.2). 

Heating a 1% (w/v) solution of ricin to >85°C for 30 min results in complete inactivation as judged by toxicity in laboratory mice (Hunt et al., 1918). Dry heat of >100°C for 60 min in an ashing oven or steam autoclave treatment at >121 °C for 1 h reduces the activity of pure ricin by >99% (Wannemacher et al., 1989). Heat inactivation of impure toxin preparations (e.g., crude ricin plant extracts) may vary. Heat-denatured ricin can undergo limited refolding (<1%) to yield active toxin. Isolated RTA and RTB are more easily inactivated by heating than is the holotoxin (Olsnes et al., 1975 Taira et al., 1978). 

Figure 5.26 Reaction catalysed by ricin A subunit and similar plant toxins.

Abrin is a plant toxin, which is closely related to ricin in terms of its structure and chemical properties. It is obtained from the seeds of Abrus pre-catorius (commonly known as jequirity bean or rosary pea ), a tropical vine cultivated as an ornamental plant in many locations. Jequirity beans are usually scarlet in colour with a black spot at one end (though less common different coloured varieties exist) and are approximately 3x8 mm in size. 

Various plant toxins, mostly ribosome-inactivating proteins (RIPs), have been identified that bind to any mammalian cell surface expressing galactose units and are subsequently internalized by RME (67). Toxins such as nigrin b (68), a-sarcin (69), ricin and saporin (70), viscumin (71), and modeccin (72) are highly toxic upon oral administration (i.e., are rapidly internalized). The possibility exists, therefore, that modified and, most important, less toxic subunits of these compound can be used to facilitate the uptake of macro-molecular compounds or microparticulates. 

Wiley RG and Oeltmann TN (1991). Ricin and related plant toxins mechanisms of action and neurobiological applications. In Keeler RF and Tu AT (eds.). Handbook of Natural Toxins. Marcel Dekker, Inc., New York. 

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