Updated: Jan 9, 2022
Author: Roy Xu
Editor: Kira Tian and Michael Zhu
Artist: Aurora Chen
Ricin is a molecule produced by the castor bean plant. It is considered one of the most lethal toxins ever discovered—a single molecule can kill an entire cell. The molecule is composed of two chains: the B chain that is responsible for the molecule’s targeting mechanism, and the A chain that contains the toxic substances. These two components, however, can be used for many different purposes.
Ricin travels through the cell by binding to the cell surface components through a form of active transport. Then, it gets engulfed in the endosome before moving to the Golgi. Then, the molecule releases its toxic component (chain A), disrupts the processes of translation by removing a specific adenine residue from the ribosomal RNA, and removes the adenine through the ribosomal elongation cycle. The ribosome would be inhibited from binding onto the translation factors that inhibit protein synthesis, disrupting cellular respiration.
Unlike amatoxin in mushrooms or batrachotoxin that helps protect pretty-looking frogs, ricin can be turned into a weapon. Due to its toxicity and how easy it is to extract the molecule, ricin has been used in many target attacks. Often the toxins are spread onto a small metal pellet where they can be delivered to the target by shooting it with an umbrella. In 1978, this strategy was used to assassinate a diplomat in London. Powdered ricin was also recently found in mail addressed to senators and the White House.
In recent years, researchers have found a way to synthesize an immunotoxin. When the molecule combines the ability of the antibody with the ricin A chain that contains the toxic substance, the molecule is then used to bind onto specific cancer cells, delivering the A chain, and thus killing pathological cells that are desirable to destroy.
Despite the hope of using ricin as a treatment for devastating diseases, there are still many who have tried to serve the “true” purpose of the molecule. Since 2010, there have been a number of arrests with ricin-related threats due to the toxicity of this molecule, punishable by up to 20-40 years. Still, it is interesting to see how we could turn poison into life-saving molecules.
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“Pdb101: Molecule of the Month: Ricin.” RCSB, pdb101.rcsb.org/motm/161.