AB-type protein toxins have a catalytic A subunit attached to a cell-binding B subunit. Ricin, Shiga toxin (Stx), exotoxin A, and diphtheria toxin are AB toxins that act within the host cytosol and kill the host cell through pathways involving the inhibition of protein synthesis. Our overall goal is to help elucidate the cellular basis of intoxication for therapeutic development. According to the current model of intoxication, the effect of AB toxins is irreversible. To test this model, we developed a system that uses flow cytometry and a fluorescent reporter to examine the cellular potency of toxins that inhibit protein synthesis. Our data show that cells can recover from intoxication: cells with a partial loss of protein synthesis will, upon removal of the toxin, increase the level of protein production and survive the toxin exposure. This work challenges the prevailing model of intoxication by suggesting ongoing toxin delivery to the cytosol is required to maintain the inhibition of protein synthesis and ultimately cause apoptosis. We also used our system to examine the basis for the greater cellular potency of Stx1 in comparison to Stx2. We found that cells intoxicated with Stx1a behave differently than those intoxicated with Stx2: cells exposed to Stx1a exhibited a population-wide loss of protein synthesis, while cells exposed to Stx2a or Stx2c exhibited a dose-dependent bimodal response in which one subpopulation of cells was unaffected (i.e., no loss of protein synthesis). Additional experiments indicated the identity of the Stx B subunit is a major factor in determining the uniform vs. bimodal response to Stx subtypes. This work provides evidence explaining, in part, the differential toxicity between Stx1 and Stx2. Overall, our collective observations provide experimental support for the development of inhibitors and post-exposure therapeutics that restrict, but not necessarily block, toxin delivery to the host cell.
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Doctor of Philosophy (Ph.D.)
College of Medicine
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Cherubin, Patrick, "AB Toxins: Recovery from Intoxication and Relative Potencies" (2019). Electronic Theses and Dissertations. 6465.
Restricted to the UCF community until August 2020; it will then be open access.