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).
Evolutionary Conservation
Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf.
Publication Abstract from PubMed
Ricin is a heterodimeric plant protein that is potently toxic to mammalian cells. Toxicity results from the catalytic depurination of eukaryotic ribosomes by ricin toxin A chain (RTA) that follows toxin endocytosis to, and translocation across, the endoplasmic reticulum membrane. To ultimately identify proteins required for these later steps in the entry process, it will be useful to express the catalytic subunit within the endoplasmic reticulum of yeast cells in a manner that initially permits cell growth. A subsequent switch in conditions to provoke innate toxin action would permit only those strains containing defects in genes normally essential for toxin retro-translocation, refolding or degradation to survive. As a route to such a screen, several RTA mutants with reduced catalytic activity have previously been isolated. Here we report the use of Saccharomyces cerevisiae to isolate temperature-dependent mutants of endoplasmic reticulum-targeted RTA. Two such toxin mutants with opposing phenotypes were isolated. One mutant RTA (RTAF108L/L151P) allowed the yeast cells that express it to grow at 37 degrees C, whereas the same cells did not grow at 23 degrees C. Both mutations were required for temperature-dependent growth. The second toxin mutant (RTAE177D) allowed cells to grow at 23 degrees C but not at 37 degrees C. Interestingly, RTAE177D has been previously reported to have reduced catalytic activity, but this is the first demonstration of a temperature-sensitive phenotype. To provide a more detailed characterization of these mutants we have investigated their N-glycosylation, stability, catalytic activity and, where appropriate, a three-dimensional structure. The potential utility of these mutants is discussed.
The isolation and characterization of temperature-dependent ricin A chain molecules in Saccharomyces cerevisiae.,Allen SC, Moore KA, Marsden CJ, Fulop V, Moffat KG, Lord JM, Ladds G, Roberts LM FEBS J. 2007 Nov;274(21):5586-99. Epub 2007 Oct 4. PMID:17916187[1]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
See Also
References
- ↑ Allen SC, Moore KA, Marsden CJ, Fulop V, Moffat KG, Lord JM, Ladds G, Roberts LM. The isolation and characterization of temperature-dependent ricin A chain molecules in Saccharomyces cerevisiae. FEBS J. 2007 Nov;274(21):5586-99. Epub 2007 Oct 4. PMID:17916187 doi:10.1111/j.1742-4658.2007.06080.x
