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

Abstract

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 Nglycosidases (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.

From Immunotoxins to Suicide Toxin Delivery Approaches: Is There a Clinical Opportunity?

“…Otherwise, bacterial toxins such as ETA or DT catalyze transfer from NAD + of ADPribose to elongation-factor EF2, thus inducing an irreversible protein synthesis arrest as a consequence of the inhibition of EF2 binding to the ribosome [16,17]. Some of these enzymes have been extensively studied in the past as toxic components of chimeric proteins called immunotoxins (ITXs) [16,17], made of a chemical or recombinant fusion between the toxin or toxic active domain and a targeting antibody or ligand binding domain. Note that, within the scope of this review, the term "immunotoxin" will be also used to indicate a broader type of chimeric toxins whose targeted domains are not exclusively made by antibodies.…”

“…Otherwise, bacterial toxins such as ETA or DT catalyze transfer from NAD + of ADPribose to elongation-factor EF2, thus inducing an irreversible protein synthesis arrest as a consequence of the inhibition of EF2 binding to the ribosome [16,17]. Some of these enzymes have been extensively studied in the past as toxic components of chimeric proteins called immunotoxins (ITXs) [16,17], made of a chemical or recombinant fusion between the toxin or toxic active domain and a targeting antibody or ligand The RIP enzymes are able to remove a specific adenine from a GAGA loop in 23S/25/28S rRNA (A4324 from rat 28S rRNA) thus irreversibly blocking translation (Figure 2). Otherwise, bacterial toxins such as ETA or DT catalyze transfer from NAD + of ADPribose to elongation-factor EF2, thus inducing an irreversible protein synthesis arrest as a consequence of the inhibition of EF2 binding to the ribosome [16,17].…”

“…Some of these enzymes have been extensively studied in the past as toxic components of chimeric proteins called immunotoxins (ITXs) [16,17], made of a chemical or recombinant fusion between the toxin or toxic active domain and a targeting antibody or ligand The RIP enzymes are able to remove a specific adenine from a GAGA loop in 23S/25/28S rRNA (A4324 from rat 28S rRNA) thus irreversibly blocking translation (Figure 2). Otherwise, bacterial toxins such as ETA or DT catalyze transfer from NAD + of ADPribose to elongation-factor EF2, thus inducing an irreversible protein synthesis arrest as a consequence of the inhibition of EF2 binding to the ribosome [16,17]. Some of these enzymes have been extensively studied in the past as toxic components of chimeric proteins called immunotoxins (ITXs) [16,17], made of a chemical or recombinant fusion between the toxin or toxic active domain and a targeting antibody or ligand binding domain.…”

Ribosome-inactivating proteins (RIPs) and their important health promoting property

“…Mannosecontaining RIPs, such as ricin, bind to mannose receptors of cell membrane through b-1,4 linked galactose residues and are internalized by virtue of clathrin-dependent endocytosis, as evidenced in Vero cells. 49,50 However, some other cytotoxic type II RIPs, such as lanceolin and stenodactylin, are internalized by mechanisms independent of clathrin-coated pits. 51 When ricin molecules enter cells, they are rstly delivered to early endosomes, from where most are recycled back to cell surface or delivered to lysosomes for proteolytical degradation.…”

Aptamer-Modified Graphene-Based Catalytic Micromotors: Off–On Fluorescent Detection of Ricin

“…To demonstrate that the observed “ Off–On ” fluorescence response is produced solely by the specific interaction with the target ricin and not by nonspecific bindings, we evaluated the specificity of the new micromotor detection system in the presence of excess nontarget proteins. For this purpose, bovine serum albumin (BSA) and saporin toxin were selected as a generic soluble protein and alternative RIP toxin, , respectively. Figure A displays the schematic illustration of FAM-aptamer-modified-rGO/Pt micromotors in a sample mixture containing ricin, BSA and saporin (Figure A­(a)), and the specific interaction of ricin with the surface-bound aptamer, accelerated by the micromotor propulsion (Figure A­(b)).…”