Bacterial Shiga-like toxins are virulence factors that constitute a significant public health threat worldwide, and the plant toxin ricin is a potential bioterror weapon. To gain access to their cytosolic target, ribosomal RNA, these toxins follow the retrograde transport route from the plasma membrane to the endoplasmic reticulum, via endosomes and the Golgi apparatus. Here, we used high-throughput screening to identify small molecule inhibitors that protect cells from ricin and Shiga-like toxins. We identified two compounds that selectively block retrograde toxin trafficking at the early endosome-TGN interface, without affecting compartment morphology, endogenous retrograde cargos, or other trafficking steps, demonstrating an unexpected degree of selectivity and lack of toxicity. In mice, one compound clearly protects from lethal nasal exposure to ricin. Our work discovers the first small molecule that shows efficacy against ricin in animal experiments and identifies the retrograde route as a potential therapeutic target.
Epsilon-toxin is produced by. Here we present evidence that epsilon-toxin cytotoxic activity is correlated with the formation of a large membrane complex (about 155 kDa) and efflux of intracellular K ؉ without entry of the toxin into the cytosol. Epsilon-toxin induced swelling, blebbing, and lysis of MDCK cells. Iodolabeled epsilon-toxin bound specifically to MDCK cell membranes at 4 and 37°C and was associated with a large complex (about 155 kDa). The binding of epsilon-toxin to the cell surface was corroborated by immunofluorescence staining. The complex formed at 37°C was more stable than that formed at 4°C, since it was not dissociated by 5% sodium dodecyl sulfate and boiling.Epsilon-toxin is produced by Clostridium perfringens types B and D and is responsible for a rapidly fatal enterotoxemia in sheep and other animals which causes heavy economic losses (24). It is synthesized as a relatively inactive prototoxin (296 amino acids) which is converted to a highly active mature protein by proteolytic removal of a basic N-terminal peptide (13 amino acids) (3, 16).Epsilon-toxin is lethal and dermonecrotic. It has been reported to increase intestinal permeability (4), to cause kidney damage (9), to elevate blood pressure (27, 39), and to cause contraction of isolated rat ileum (40). A basic property of epsilon-toxin is that it increases vascular permeability. The toxin binds to vascular endothelial cells and causes severe vascular damage and edema in various organs (brain, heart, lung, and kidney) (5, 9). It was reported that the major pathological changes caused by enterotoxemia appear to occur in the brain (12). Moreover, it was shown that labeled toxin specifically accumulates in the brains of mice after intravenous injection and that the lethal activity of the toxin depends on its specific binding in the brain, probably to a sialoglycoprotein (28,29). Certain amino acids of epsilon-toxin, such as histidine, tryptophan, and aspartic or glutamic acid have been found to be essential for its biological activity (35)(36)(37)(38).Recently, it has been found that epsilon-toxin has 20 and 27% identity with Mtx2 and Mtx3 toxins, respectively, of Bacillus sphaericus (22, 43) and 26.5% identity with the open reading frame c53 of Bacillus thuringiensis. However, the mechanism of action of these mosquitocidal toxins is unknown.The Madin-Darby canine kidney (MDCK) cell line was found to be susceptible to epsilon-toxin. The alteration of cell viability determined by the conversion of 5-(3-carboxymethoxyphenyl)-2-(4,5-dimethylthiazolyl)-3-(4-sulfophenyl) tetrazolium to a water-soluble formazan by the mitochondrial cytochrome systems or by the neutral red assay (an indicator of lysosomal integrity) was correlated with the lethal activity of epsilon-toxin in mice (21, 30). The cytotoxic effects were found to be very rapid (2.5 min) and potentiated by EDTA (21). The morphological effects of epsilon-toxin on cells included a condensation of the nucleus and a progressive swelling of the cells (13). The permeability of polarized MD...
At the cellular level, a small number of protein molecules (receptors) can induce significant cellular responses, emphasizing the importance of molecular detection of trace amounts of protein on single living cells. In this study, we designed and synthesized silver nanoparticle biosensors (AgMMUA-IgG) by functionalizing 11.6 +/- 3.5-nm Ag nanoparticles with a mixed monolayer of 11-mercaptoundecanoic acid (MUA) and 6-mercapto-1-hexanol (1:3 mole ratio) and covalently conjugating IgG with MUA on the nanoparticle surface. We found that the nanoparticle biosensors preserve their biological activity and photostability and can be utilized to quantitatively detect individual receptor molecules (T-ZZ), map the distribution of receptors (0.21-0.37 molecule/microm(2)), and measure their binding affinity and kinetics at concentrations below their dissociation constant on single living cells in real time over hours. The dynamic range of detection is 0-50 molecules per cell. We also found that the binding rate (2-27 molecules/min) is highly dependent upon the coverage of receptors on living cells and their ligand concentration. The binding association and dissociation rate constants and affinity constant are k1 = (9.0 +/- 2.6) x 10(3) M(-1) s(-1), k(-1) = (3.0 +/- 0.4) x 10(-4) s(-1), and KB = (4.3 +/- 1.1) x 10(7) M(-1), respectively.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.