Structure and properties of ricin – the toxic protein of Ricinus communis

Ricin is a heterodimeric protein that consists of A and B subunits that can be produced in the seeds of the castor oil plant Ricinus communis. Its large quantities are accumulated in byproducts generated during the extraction of castor oil, widely used in the cosmetic and pharmaceutical industry. Ricin is one of the most potent toxins. Toxic effects of ricin are caused by its ability to inhibit protein synthesis and the level of toxicity depends on both dose and route of exposure. There are three route of administration of ricin: oral ingestion, parenteral (injectable) or inhalation. The clinical presentation of ricin toxicity depends on the route of administration. Toxin causes inflammation, gastrointestinal haemorrhages, renal tubular necrosis or hypoglycemia. Although ricin can be lethal, it has the potential for therapeutic use. Ricin A-chain is one of the first examples of a toxin coupled to monoclonal antibodies against cell surface proteins and is used experimentally for the treatment of various cancers. This article discusses the structure of ricin, the mechanism of its synthesis and describes the biological activity of this protein.