Ricin and related Type II ribosome-inactivating proteins (RIPs)

Ricin is a highly potent Type II ribosome-inactivating protein (RIP) derived from the castor bean plant, Ricinus communis. It consists of two polypeptide chains, A and B, linked by a critical disulfide bond; the B-chain (RTB) acts as a lectin that facilitates cell entry by binding to surface carbohydrates, while the A-chain (RTA) functions as an N-glycosylase that irreversibly inactivates the 28S ribosomal RNA. Once inside the cytosol, the A-chain depurinates the sarcin/ricin loop of the ribosome, effectively halting protein synthesis and leading to rapid cell death and systemic organ failure. Related toxins, such as abrin and Shiga toxin, share this disulfide-linked structure and lethal mechanism of action. Therapeutic research is primarily focused on developing neutralizing antibodies, small-molecule inhibitors of the A-chain, and vaccines to prevent or mitigate the effects of exposure, as there are currently no FDA-approved antidotes.

Other names

Ricinus communis agglutininAbrinShiga toxinModeccinViscuminVolkensinType II RIPs

Irreversible depurination of the adenine residue at position 4324 (A4324) within the sarcin/ricin loop (SRL) of 28S rRNA by the A-chain; B-chain mediated cell entry via binding to galactose or N-acetylgalactosamine residues.