Ricin
Cleaved into the following 3 chains:
- Ricin A chain EC=3.2.2.22 (Alternative name(s):rRNA N-glycosidase)
- Linker peptide
- Ricin B chain
- Organism
- Ricinus communis (Castor bean)
- Function
- Ricin is highly toxic to animal cells and to a lesser extent to plant cells. The A chain acts as a glycosidase that removes a specific adenine residue from an exposed loop of the 28S rRNA (A4324 in mammals), leading to rRNA breakage. As this loop is involved in elongation factor binding, modified ribosomes are catalytically inactive and unable to support protein synthesis. The A chain can inactivate a few thousand ribosomes per minute, faster than the cell can make new ones. Therefore a single A chain molecule can kill an animal cell. The B chain binds to beta-D-galactopyranoside moieties on cell surface glycoproteins and glycolipids and facilitates the entry into the cell of the A chain; B chains are also responsible for cell agglutination (Lectin activity).
- Catalytic activity
- Endohydrolysis of the N-glycosidic bond at one specific adenosine on the 28S rRNA.
- Subunit structure
- Disulfide-linked dimer of A and B chains.
- Domain
- The B chain is composed of two domains, each domain consists of 3 homologous subdomains (alpha, beta, gamma).
- Biotechnological use
- A deglycosylated A chain may be linked to monoclonal antibodies to produce immunotoxins exploited in cancer treatment. However, a point mutation should be introduced to eliminate vascular leak syndrome, a side effect resulting from endothelial damage.
LSequence similarities:In the N-terminal section; belongs to the ribosome-inactivating protein family. Type 2 RIP subfamily.
Contains 2 ricin B-type lectin domains.
