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Inactivation of Ras by Clostridium sordellii lethal toxin-catalyzed glucosylation
1Institut für Pharmakologie und Toxikologie der Universität Freiburg, Hermann-Herder-Strasse 5, D-79104 Freiburg, Germany.
Abstract:
The lethal toxin (LT) from Clostridium sordellii belongs to the family of large clostridial cytotoxins causing morphological alterations in cultured cell lines accompanied by destruction of the actin cytoskeleton. C. sordellii LT exhibits 90% homology to Clostridium difficile toxin B, which has been recently identified as a monoglucosyltransferase (Just, I., Selzer, J., Wilm, M., von Eichel-Streiber, C., Mann, M., and Aktories, K. (1995) Nature 375, 500-503). We report here that LT too is a glucosyltransferase, which uses UDP-glucose as cosubstrate to modify low molecular mass GTPases. LT selectively modifies Rac and Ras, whereas the substrate specificity of toxin B is confined to the Rho subfamily proteins Rho, Rac, and Cdc42, which participate in the regulation of the actin cytoskeleton. In Rac, both toxin B and LT share the same acceptor amino acid, threonine 35. Glucosylation of Ras by LT results in inhibition of the epidermal growth factor-stimulated p42/p44 MAP-kinase signal pathway. LT is the first bacterial toxin to inactivate Ras in intact cells.
Insights
Clostridium sordellii lethal toxin (LT) is a glucosyltransferase that modifies GTPases. Unlike Clostridium difficile toxin B, LT also inactivates Ras, inhibiting a key cell signaling pathway.
Area of Science:
- Microbiology
- Cell Biology
- Toxicology
Background:
- Large clostridial cytotoxins, including Clostridium sordellii lethal toxin (LT), disrupt cell morphology and the actin cytoskeleton.
- Clostridium difficile toxin B is a known monoglucosyltransferase with specificity for Rho subfamily GTPases.
- LT shares high homology with C. difficile toxin B, suggesting a similar enzymatic mechanism.
Purpose of the Study:
- To determine the enzymatic activity and substrate specificity of Clostridium sordellii lethal toxin (LT).
- To compare the substrate modification of LT with that of Clostridium difficile toxin B.
- To investigate the effect of LT-mediated modification on cellular signaling pathways.
Main Methods:
- Enzymatic assays using UDP-glucose as a cosubstrate to identify LT's target proteins.
- Analysis of substrate specificity by examining modifications of low molecular mass GTPases.
- Investigation of the impact of LT on the epidermal growth factor-stimulated p42/p44 MAP-kinase pathway.
Main Results:
- Clostridium sordellii LT functions as a glucosyltransferase, modifying low molecular mass GTPases.
- LT selectively modifies Rac and Ras proteins; toxin B modifies Rho, Rac, and Cdc42.
- LT-mediated glucosylation of Ras inhibits the p42/p44 MAP-kinase signaling pathway.
- LT is the first bacterial toxin identified to inactivate Ras in intact cells.
Conclusions:
- Clostridium sordellii LT possesses distinct substrate specificity compared to Clostridium difficile toxin B, targeting Ras in addition to Rac.
- The inactivation of Ras by LT has significant implications for understanding bacterial toxin mechanisms and cellular signaling.
- LT represents a novel bacterial toxin capable of disrupting Ras-mediated cellular processes.