Author ORCID Identifier
Date of Award
Spring 5-2026
Document Type
Thesis (Ph.D.)
Department or Program
Chemistry
First Advisor
F. Jon Kull
Second Advisor
Charles R. Midgett
Abstract
Pathogenic Vibrio bacteria, such as V. cholerae and V. parahaemolyticus, colonize in the human small intestine to cause severe gastrointestinal disease. During the infection, these bacteria encounter bile salts, antimicrobial cholesterol metabolites secreted into the intestine. Pathogenic Vibrio species have evolved to utilize bile salts as signals to regulate virulence. The signaling depends in part on ToxRS, a conserved co-component transmembrane transcription regulator. ToxRS consists of the transcription factor ToxR and its membrane-tethered binding partner ToxS. ToxS is required for ToxR stability and full transcriptional activity. Although bile salts are known to influence ToxRS-dependent virulence gene expression, the molecular mechanism of how ToxRS senses bile salts is unclear. In particular, whether ToxS participates directly in bile sensing is unknown.
To address this question, the crystal structures of V. parahaemolyticus ToxS periplasmic domain (ToxSp) were determined in apo and glycocholate-bound states. The apo structure reveals that ToxSp adopts an eight-stranded broken β-barrel monomer with a solvent-accessible binding pocket. The glycocholate-bound structure reveals a strand-swapped homodimer with the β8 strands exchanged between monomers, and three glycocholate molecules are bound at the dimer interface. Furthermore, the glycocholate-bound conformation shifts ToxSp toward a more open barrel that resembles the ToxR-bound state observed in a previously reported V. cholerae ToxRS structure. A structural similarity search shows that ToxSp is related to chaperone proteins, consistent with its established role in stabilizing ToxR. These structures together suggest a heterotetramer model in which bile salt bound ToxSp can facilitate the assembly of an active ToxRS complex.
To test the heterotetramer model, crystallization of the V. parahaemolyticus ToxRS periplasmic complex (ToxRSp) was attempted in both apo and bile salt-bound forms. The apo ToxRSp complex produced crystals that diffract to 3.0 Å resolution.
The structures presented in this work suggest that ToxS can directly bind bile salts and suggest that ToxS can function as a bile sensor within the ToxRS system.
Recommended Citation
Kim, Minje, "Understanding the role of ToxS as a bile sensing component of the ToxRS virulence regulatory system in Vibrio spp." (2026). Dartmouth College Ph.D Dissertations. 488.
https://digitalcommons.dartmouth.edu/dissertations/488
Included in
Amino Acids, Peptides, and Proteins Commons, Bacterial Infections and Mycoses Commons, Bacteriology Commons, Biochemistry Commons, Biological Factors Commons, Biophysics Commons, Digestive System Diseases Commons, Molecular Biology Commons, Other Immunology and Infectious Disease Commons, Other Physiology Commons, Pathogenic Microbiology Commons, Structural Biology Commons
