Ricin and Saporin: Plant Enzymes for the Research and the Clinics

Many plants produce enzymes with N-glycosidase activity, also known as Ribosome Inactivating Proteins. These proteins remove a specific adenine residue from the ribosomal RNA (28S in eukaryotes) inducing the block of protein synthesis by inhibiting the binding of the Elongation Factor 2. Both eukaryotic and prokaryotic ribosomes (with different sensitivity) can irreversibly be damaged by the action of these enzymes, suggesting their use as cytotoxic drugs. In fact several applications of targeted N-glycosidases have been developed (i.e. immunotoxins) for the treatment of human diseases such as leukaemia, but biotechnological development has furthermore suggested new applications of targeted N-glycosidases (i.e. Ig192-saporin) that are now used as powerful tools for cell biology research. The high number of enzymes available and the possibility to express these proteins as recombinant products, allow to predict new formulations and applications discussed in this paper starting from the example of the model toxins ricin and saporin.