Structural highlights
Function
RICI_RICCO 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).
Publication Abstract from PubMed
Ricin toxin A-chain (RTA), a toxic protein from Ricinus communis, inactivates ribosomes to induce toxicity. The active site of RTA consists of two binding pockets. Many studies have focused on developing RTA inhibitors that can simultaneously bind to these critical pockets; however, almost all the inhibitors developed so far interact with only one pocket. In the present study, we discovered that pterin-7-carboxamides with aromatic l-amino acid pendants interacted with the active site of the enzyme in a 2-to-1 mode, where one inhibitor molecule bound to the primary pocket and the second one entered the secondary pocket in the active site of RTA. X-ray crystallographic analysis of inhibitor/RTA complexes revealed that the conformational changes of Tyr80 and Asn122 in RTA were critical for triggering the entry of inhibitor molecules into the secondary pocket of the RTA active site.
Conformational change in ricin toxin A-Chain: A critical factor for inhibitor binding to the secondary pocket.,Goto M, Higashi S, Ohba T, Kawata R, Nagatsu K, Suzuki S, Anslyn EV, Saito R Biochem Biophys Res Commun. 2022 Oct 30;627:1-4. doi: 10.1016/j.bbrc.2022.08.008. , Epub 2022 Aug 13. PMID:35998389[1]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Goto M, Higashi S, Ohba T, Kawata R, Nagatsu K, Suzuki S, Anslyn EV, Saito R. Conformational change in ricin toxin A-Chain: A critical factor for inhibitor binding to the secondary pocket. Biochem Biophys Res Commun. 2022 Oct 30;627:1-4. doi: 10.1016/j.bbrc.2022.08.008. , Epub 2022 Aug 13. PMID:35998389 doi:http://dx.doi.org/10.1016/j.bbrc.2022.08.008
