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Structure-based discovery of a pore-binding ligand: towards assembly inhibitors for cholera and related AB5 toxins
B T Hovey1, C L Verlinde, E A Merritt
1Department of Biochemistry, University of Washington, Seattle, 98195, USA.
Abstract:
Cholera toxin (CT) and Escherichia coli heat-labile enterotoxin (LT) are two closely related multi-subunit AB5 proteins responsible for significant morbidity and mortality worldwide. An attractive strategy to prevent disease by these organisms is to interfere with the assembly process of these toxins, since prevention of toxin formation is better than preventing the effects of a toxin which is already formed. The B subunits form a ring with a central pore which surrounds the C-terminal residues of the A subunit. Low molecular mass compounds which would bind in the pore are likely to inhibit proper assembly of the AB5 toxins. In a pharmacophore search based on two side-chains of the A subunit, 3-methylthio-1,4-diphenyl-1H-1, 3,4-triazolium (MDT) was identified as a candidate ligand which might "plug" the pore. A 2.0 A co-crystal structure revealed that a triplet of MDTs indeed bound to the targeted region in two independent LT B pentamers in a remarkably similar manner. Clearly, MDT is a lead for developing assembly antagonists of CT and LT.
Insights
Researchers identified 3-methylthio-1,4-diphenyl-1H-1,3,4-triazolium (MDT) as a potential inhibitor for cholera toxin (CT) and E. coli heat-labile enterotoxin (LT) assembly. MDT may plug the toxin pore, preventing disease.
Area of Science:
- Microbiology
- Structural Biology
- Biochemistry
Background:
- Cholera toxin (CT) and E. coli heat-labile enterotoxin (LT) are AB5 toxins causing significant global disease.
- Interfering with toxin assembly is a promising preventative strategy.
- The B subunits form a pore that interacts with the A subunit.
Purpose of the Study:
- To identify small molecules that inhibit CT and LT assembly.
- To investigate the potential of plugging the B subunit pore to prevent toxin formation.
Main Methods:
- Pharmacophore search based on CT/LT A subunit side-chains.
- Co-crystallization and structural analysis of LT B pentamers with identified ligands.
Main Results:
- 3-methylthio-1,4-diphenyl-1H-1,3,4-triazolium (MDT) was identified as a candidate ligand.
- A crystal structure revealed MDT binding within the LT B pentamer pore.
- MDT triplets bound to the targeted pore region in LT B pentamers.
Conclusions:
- MDT is a lead compound for developing assembly antagonists of CT and LT.
- Targeting the toxin pore offers a novel strategy for preventing bacterial toxin-mediated diseases.