Ricin toxin B subunit (RTB)

The Ricin toxin B subunit (RTB) is the non-catalytic, lectin component of the potent Type II ribosome-inactivating protein (RIP) ricin, derived from the castor bean plant Ricinus communis [2, 10]. RTB functions as the delivery vehicle for the enzymatic A subunit (RTA), binding specifically to terminal galactose and N-acetylgalactosamine residues on cell surface glycoproteins and glycolipids [5, 14]. This binding triggers receptor-mediated endocytosis and initiates the retrograde transport of the toxin through the Golgi apparatus to the endoplasmic reticulum (ER) [10, 16]. In the ER, the disulfide bond connecting the two subunits is reduced, allowing RTA to translocate into the cytosol where it irreversibly inactivates ribosomes [14, 15]. Due to its essential role in mediating toxin entry, RTB is a primary target for the development of neutralizing monoclonal antibodies and vaccines intended to provide protection against ricin poisoning, a significant concern in biodefense [5, 11]. Furthermore, RTB's high affinity for cell surfaces has led to its use in biotechnology as a component of immunotoxins for cancer therapy, where it is engineered to deliver cytotoxic payloads to malignant cells [1, 8]. However, the use of RTB-containing compounds faces challenges such as off-target toxicity and the potential for vascular leak syndrome [1, 15]. Monitoring for ricin exposure often involves detecting the biomarker ricinine or measuring RTB-specific antibody titers in the blood [4, 17].

Other names

Ricin B chainRTBRicinus communis agglutinin B subunitLectin B-chain

Neutralization of toxin binding to cell surface receptors and inhibition of retrograde transport to prevent cellular entry of the toxic A subunit.