7mlt
Crystal structure of ricin A chain in complex with 5-(2-ethylphenyl)thiophene-2-carboxylic acid
Structural highlights
FunctionRICI_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 PubMedRicin toxin A subunit (RTA) is the catalytic subunit of ricin, which depurinates an adenine from the sarcin/ricin loop in eukaryotic ribosomes. There are no approved inhibitors against ricin. We used a new strategy to disrupt RTA-ribosome interactions by fragment screening using surface plasmon resonance. Here, using a structure-guided approach, we improved the affinity and inhibitory activity of small-molecular-weight lead compounds and obtained improved compounds with over an order of magnitude higher efficiency. Four advanced compounds were characterized by X-ray crystallography. They bind at the RTA-ribosome binding site as the original compound but in a distinctive manner. These inhibitors bind remotely from the catalytic site and cause local conformational changes with no alteration of the catalytic site geometry. Yet they inhibit depurination by ricin holotoxin and inhibit the cytotoxicity of ricin in mammalian cells. They are the first agents that protect against ricin holotoxin by acting directly on RTA. Synthesis and Structural Characterization of Ricin Inhibitors Targeting Ribosome Binding Using Fragment-Based Methods and Structure-Based Design.,Li XP, Harijan RK, Cao B, Kahn JN, Pierce M, Tsymbal AM, Roberge JY, Augeri D, Tumer NE J Med Chem. 2021 Oct 28;64(20):15334-15348. doi: 10.1021/acs.jmedchem.1c01370., Epub 2021 Oct 14. PMID:34648707[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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