View All Items
(1 - 3 of 3)
- Title
- CELLULAR AND MOLECULAR MECHANISMS OF TOXIN RESISTANCE FOR ENDOPLASMIC RETICULUM TRANSLOCATING TOXINS.
- Creator
-
Massey, Christopher, Teter, Kenneth, University of Central Florida
- Abstract / Description
-
The endoplasmic reticulum (ER) is the site of co- and post-translational modification for secretory proteins. In order to prevent vesicular transport and secretion of misfolded or misassembled proteins, a highly regulated mechanism called ER-associated degradation (ERAD) is employed. This pathway recognizes misfolded proteins in the ER lumen and targets them to the cytosol for ubiquitination and subsequent degradation via the 26S proteasome. Sec61 and Derlin-1 are ER pores through which...
Show moreThe endoplasmic reticulum (ER) is the site of co- and post-translational modification for secretory proteins. In order to prevent vesicular transport and secretion of misfolded or misassembled proteins, a highly regulated mechanism called ER-associated degradation (ERAD) is employed. This pathway recognizes misfolded proteins in the ER lumen and targets them to the cytosol for ubiquitination and subsequent degradation via the 26S proteasome. Sec61 and Derlin-1 are ER pores through which export occurs. AB-type protein toxins such as cholera toxin (CT), Shiga toxin (ST), exotoxin A (ETA), and ricin have evolved means of exploiting the ERAD pathway in order to reach their cytosolic targets. AB-type protein toxins consist of a catalytic A-subunit and a cell-binding B-subunit. The B-subunit recognizes cell surface receptors for the toxin. This begins a series of vesicle trafficking events, collectively termed retrograde trafficking, that lead to the ER. Dissociation of the A and B subunits occurs in the ER, and only the A subunit enters the cytosol. The exact mechanism of A subunit translocation from the ER to the cytosol is unknown. Toxin translocation occurs through a pore in the ER membrane. Exit through the pore requires the toxin to be in an unfolded conformation. The current model for toxin translocation proposes that ER chaperones actively unfold the toxin A chain for translocation. After the translocation event, the toxin spontaneously refolds to an active conformation. Our model suggests that unfolding in the ER is spontaneous and refolding in the cytosol is dependent upon cytosolic chaperones. Based on our model, we hypothesize that blockage of the A subunit unfolding and/or the ERAD translocation step will confer a phenotype of non-harmful multi-toxin resistance to cells. In support of this model, we have shown that, at 37ºC, the isolated catalytic subunit of cholera toxin (CTA1) is in an unfolded and protease sensitive confirmation that identifies the toxin as misfolded by the ERAD pathway. Stabilization of CTA1 via glycerol inhibits the loss of its tertiary structure. This stabilization results in decreased translocation from the ER to the cytosol and increased secretion of CTA1 to the extracellular medium. Treatment with glycerol also prevents CTA1 degradation by the 20S proteasome in vitro. These data indicate that the thermal stability of CTA1 plays an important role in intoxication. These data also suggest that stabilization of CTA1 tertiary structure is a potential target for therapeutic agents. Our model asserts that CTA1 behaves as a normal ERAD substrate upon dissociation from the holotoxin. In support of this model, we have shown that the ER luminal protein HEDJ, known to be involved in ERAD, interacts with CTA1. The interactions between HEDJ and CTA1 occur only at temperatures in which the toxin is in an unfolded conformation. We have also shown that HEDJ does not affect the thermally stability of CTA1 since there is no alteration in its pattern of temperature-dependent protease sensitivity. Alteration of the normal HEDJ-CTA1 interaction via a dominant-negative HEDJ construct resulted in decreased translocation from the ER to the cytosol and, as a result, decreased intoxication. Our work demonstrated toxin resistance can result through effects on toxin structure or ERAD chaperones. To identify other potential inhibitors, we developed a novel assay to detect the activity of other AB toxins and compared it with an established toxicity assay. We generated a Vero cell line that expressed a destabilized variant of enhanced green fluorescent protein (EGFP). These cells were used to monitor the Stx-induced inhibition of protein synthesis by monitoring the loss of EGFP fluorescence from cells. We screened a panel of 13 plant compounds, and indentified grape seed extract and grape pomace extract as inhibitors of Stx activity. Grape seed extract and grape pomace extract were also shown to block the toxic activities of ETA and ricin, providing the basis for a future high-throughput screen for multi-toxin inhibitors.
Show less - Date Issued
- 2009
- Identifier
- CFE0002925, ucf:47999
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002925
- Title
- Unraveling PDI and its Interaction with AB Toxins.
- Creator
-
Guyette, Jessica, Teter, Kenneth, Self, William, Jewett, Travis, Tatulian, Suren, University of Central Florida
- Abstract / Description
-
Protein disulfide isomerase (PDI) is an essential endoplasmic reticulum (ER) protein that acts as both an oxidoreductase and chaperone. It exhibits substantial flexibility and undergoes cycles of unfolding and refolding in its interaction with cholera toxin (Ctx), which is a unique property of PDI. This unfolding allows PDI to disassemble the Ctx holotoxin, which is required for Ctx activity. Here, we investigated the unfolding and refolding property of PDI and how this affects its...
Show moreProtein disulfide isomerase (PDI) is an essential endoplasmic reticulum (ER) protein that acts as both an oxidoreductase and chaperone. It exhibits substantial flexibility and undergoes cycles of unfolding and refolding in its interaction with cholera toxin (Ctx), which is a unique property of PDI. This unfolding allows PDI to disassemble the Ctx holotoxin, which is required for Ctx activity. Here, we investigated the unfolding and refolding property of PDI and how this affects its interaction with bacterial toxins. PDI showed remarkable redox-linked conformational resilience that allows it to refold after being thermally stressed. Deletion constructs of PDI showed that both active domains play opposing roles in stability, and can both refold from an unfolded state, indicating that either domain could unfold during its interaction with Ctx. Its ability to refold suggests that the cycle of unfolding and refolding with Ctx is a normal mechanism that prevents protein aggregation. Disruption of this cycle with the polyphenol, quercetin-3-rutinoside, prevented the disassembly of Ctx, which blocked Ctx intoxication of cultured cells. Loss of PDI function was also found to inhibit intoxication with Escherichia coli heat-labile toxin but not with ricin and Shiga toxins. Toxin structure also contributes to efficiency of PDI binding and disassembly, which may explain the differential potencies between toxins. While Ctx and Ltx share similar structures, Ctx is more potent and efficiently disassembled compared to Ltx. We believe that PDI-mediated disassembly is the rate-limiting step in intoxication, thus dictating toxin potency. Overall, PDI can be targeted for a potential therapeutic for many bacterial toxins because of its unique unfolding properties and its key role in cell intoxication.
Show less - Date Issued
- 2019
- Identifier
- CFE0007646, ucf:52511
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007646
- Title
- The Anti-toxin Properties of Grape Seed Phenolic Compounds.
- Creator
-
Cherubin, Patrick, Teter, Kenneth, Zervos, Antonis, Roy, Herve, Phanstiel, Otto, University of Central Florida
- Abstract / Description
-
Corynebacterium diphtheriae, Pseudomonas aeruginosa, Ricinus communis, Shigella dysentariae, and Vibrio cholerae produce AB toxins which share the same basic structural characteristics: a catalytic A subunit attached to a cell-binding B subunit. All AB toxins have cytosolic targets despite an initial extracellular location. AB toxins use different methods to reach the cytosol and have different effects on the target cell. Broad-spectrum inhibitors against these toxins are therefore hard to...
Show moreCorynebacterium diphtheriae, Pseudomonas aeruginosa, Ricinus communis, Shigella dysentariae, and Vibrio cholerae produce AB toxins which share the same basic structural characteristics: a catalytic A subunit attached to a cell-binding B subunit. All AB toxins have cytosolic targets despite an initial extracellular location. AB toxins use different methods to reach the cytosol and have different effects on the target cell. Broad-spectrum inhibitors against these toxins are therefore hard to develop because they use different surface receptors, entry mechanisms, enzyme activities, and cytosolic targets.We have found that grape seed extract provides resistance to five different AB toxins: diphtheria toxin (DT), P. aeruginosa exotoxin A (ETA), ricin, Shiga toxin, and cholera toxin (CT). To identify individual compounds in grape seed extract that are capable of inhibiting the activities of these AB toxins, we screened twenty common phenolic compounds of grape seed extract for anti-toxin properties. Three compounds inhibited DT, four inhibited ETA, one inhibited ricin, and twelve inhibited CT. Additional studies were performed to determine the mechanism of inhibition against CT. Two compounds inhibited CT binding to the cell surface and even stripped bound CT off the plasma membrane of a target cell. Two other compounds inhibited the enzymatic activity of CT. We have thus identified individual toxin inhibitors from grape seed extract and some of their mechanisms of inhibition against CT. This work will help to formulate a defined mixture of phenolic compounds that could potentially be used as a therapeutic against a broad range of AB toxins.
Show less - Date Issued
- 2014
- Identifier
- CFE0005315, ucf:50510
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005315
