Abstract

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 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.

Notes

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Graduation Date

2019

Semester

Summer

Advisor

Teter, Kenneth

Degree

Doctor of Philosophy (Ph.D.)

College

College of Medicine

Department

Biomedical Sciences

Degree Program

Biomedical Sciences

Format

application/pdf

Identifier

CFE0007646

URL

http://purl.fcla.edu/fcla/etd/CFE0007646

Language

English

Release Date

August 2019

Length of Campus-only Access

None

Access Status

Doctoral Dissertation (Open Access)

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