Ricin toxin B-chain (RTB)

Ricin toxin B-chain (RTB) is the 32 kDa lectin subunit of the ricin toxin, a potent type II ribosome-inactivating protein (RIP) derived from the castor bean plant, Ricinus communis (UniProt: P02879). RTB is responsible for the toxin's ability to enter host cells by binding to terminal galactose or N-acetylgalactosamine residues on cell surface glycoproteins and glycolipids (PubMed: 21835361). Following binding, RTB mediates the receptor-mediated endocytosis and subsequent retrograde transport of the toxin from the cell surface through the Golgi apparatus to the endoplasmic reticulum (ER). In the ER, the disulfide bond linking RTB to the catalytic A-chain (RTA) is reduced, allowing RTA to translocate into the cytosol where it halts protein synthesis by depurinating the sarcin/ricin loop of 28S rRNA (StatPearls: Ricin Toxicity). As the essential mediator of cellular entry, RTB is a primary target for the development of neutralizing antibodies and vaccines, such as RiVax and RVEc, designed to provide immunity against ricin poisoning (PubMed: 25547321). Additionally, RTB's high affinity for cell surfaces has led to its investigation as a delivery vehicle for various therapeutic payloads and as a component of immunotoxins in cancer research (PubMed: 12165534).

Other names

RTBRicin B-chainLectin subunit of ricinRicin agglutinin B-chain

Neutralization of cell-surface binding and inhibition of retrograde transport to prevent the catalytic A-chain from entering the cytosol.