Abstract
Experiments were done to help localize the minimum essential domain within the botulinum toxin molecule that is necessary for binding and transport across human gut epithelial cells. The data demonstrated that the neurotoxin alone, in the absence of auxiliary proteins, undergoes transcytosis. The neurotoxin by itself was examined in the single chain (unnicked serotype B) and dichain (nicked serotype B, nicked serotype A) forms, and all displayed the ability to bind and penetrate epithelial barriers. In addition, the single chain and dichain molecules were examined in the oxidized and reduced states, and again all forms were transported. To further define the minimum essential domain, experiments were done with two toxin fragments: 1) the heavy chain, which was derived from native toxin, and 2) the carboxy-terminal portion of the heavy chain, which was generated by recombinant techniques. Interestingly, both fragments were fully competent in crossing epithelial barriers. These data suggest that a polypeptide derived from the toxin could be used as a carrier domain to transport other molecules across epithelial cells. In related experiments, physiological (i.e., potassium depletion) and pharmacological (i.e., chlorpromazine) manipulations were used to implicate clathrin-coated pits/vesicles as the structures responsible for endocytosis of toxin.
Footnotes
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This work was supported by National Institutes of Health Grants NS-22153 and GM57342 and by National Institutes of Health Contracts AI56456 and AI30028.
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DOI: 10.1124/jpet.104.066845.
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ABBREVIATIONS: BoNT, botulinum neurotoxin; HC-100, 100-kDa toxin heavy chain; HC-50, 50-kDa carboxy-terminal heavy chain fragment; HA, hemagglutinin; NTNH, nontoxin nonhemagglutinin; DTT, dithiothreitol; MDCK, Madin-Darby canine kidney; TEER, transepithelial electrical resistance; SAR, structure-activity relationships.
- Received February 11, 2004.
- Accepted May 12, 2004.
- The American Society for Pharmacology and Experimental Therapeutics
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