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Description

Ricin is a dimeric toxin derived from Ricinus communis (Caster bean). It is composed of a sugar-binding subunit (B chain) that attached to cell surface receptors and facilitate the entry of toxin into the target cell and a second subunit (A chain), which has glycosidase activity that inactivates ribosomes by depurinating a single adenosine residue from an exposed loop of the 28S ribosomal RNA. The toxic effects of Ricin are attributed to the A chain. Ricin B chain is shown to be a lectin that binds to galactosides found at the cell surface in a non-cooperative manner. It has two Ricin-B type lectin domains (aa 7-134 and 137-261). The mode of galactose binding is reported to be nearly identical at the two sites. Clone RBC11 is shown to block binding of Ricin to the cell. (Ref.: Maddaloni, M., et al. (2004). J. Immunol. 172, 6221-6228, Rutenber, E., et al. (1987). Nature. 326(6113):624-626).