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Effects of Small Molecule Calcium-Activated Chloride Channel Inhibitors on Structure and Function of Accessory Cholera Enterotoxin (Ace) of Vibrio cholerae.

Chatterjee T, Sheikh IA, Chakravarty D, Chakrabarti P, Sarkar P, Saha T, Chakrabarti MK, Hoque KM - PLoS ONE (2015)

Bottom Line: Biophysical studies indicate that the unfolding (induced by urea) free energy increases upon binding CaCCinh-A01 and DGA, compared to native Ace, whereas binding of tannic acid destabilizes the protein.In contrast, binding to tannic acid had the opposite effect, indicating the loss of protein secondary structure.The efficacy of tannic acid in mouse model suggests that the targeted modulation of Ace structure may be of therapeutic benefit for gastrointestinal disorders.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Bose Institute, P1/12 CIT Scheme VIIM, Kolkata, 700054, India.

ABSTRACT
Cholera pathogenesis occurs due to synergistic pro-secretory effects of several toxins, such as cholera toxin (CTX) and Accessory cholera enterotoxin (Ace) secreted by Vibrio cholerae strains. Ace activates chloride channels stimulating chloride/bicarbonate transport that augments fluid secretion resulting in diarrhea. These channels have been targeted for drug development. However, lesser attention has been paid to the interaction of chloride channel modulators with bacterial toxins. Here we report the modulation of the structure/function of recombinant Ace by small molecule calcium-activated chloride channel (CaCC) inhibitors, namely CaCCinh-A01, digallic acid (DGA) and tannic acid. Biophysical studies indicate that the unfolding (induced by urea) free energy increases upon binding CaCCinh-A01 and DGA, compared to native Ace, whereas binding of tannic acid destabilizes the protein. Far-UV CD experiments revealed that the α-helical content of Ace-CaCCinh-A01 and Ace-DGA complexes increased relative to Ace. In contrast, binding to tannic acid had the opposite effect, indicating the loss of protein secondary structure. The modulation of Ace structure induced by CaCC inhibitors was also analyzed using docking and molecular dynamics (MD) simulation. Functional studies, performed using mouse ileal loops and Ussing chamber experiments, corroborate biophysical data, all pointing to the fact that tannic acid destabilizes Ace, inhibiting its function, whereas DGA stabilizes the toxin with enhanced fluid accumulation in mouse ileal loop. The efficacy of tannic acid in mouse model suggests that the targeted modulation of Ace structure may be of therapeutic benefit for gastrointestinal disorders.

No MeSH data available.


Related in: MedlinePlus

(A) Quenching of tryptophan fluorescence of Ace with CaCC inhibitors. (B) log [(Fo –Fc)/Fc] versus log [ligand] plot for the fluorescence quenching of Ace with CaCC inhibitors.
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pone.0141283.g004: (A) Quenching of tryptophan fluorescence of Ace with CaCC inhibitors. (B) log [(Fo –Fc)/Fc] versus log [ligand] plot for the fluorescence quenching of Ace with CaCC inhibitors.

Mentions: Quenching of tryptophan fluorescence is frequently used to study protein-ligand interaction [29,30]. Addition of CaCC inhibitors resulted in quenching of tryptophan fluorescence of Ace. The quenching data are presented as a Stern-Volmer plot, showing F0/Fc versus concentration of small molecules (Fig 4A). A plot of log[(F0−Fc)/Fc].versus log([Q]) for Ace-small molecules interaction using least-squares analysis gave the binding constants (Fig 4B).


Effects of Small Molecule Calcium-Activated Chloride Channel Inhibitors on Structure and Function of Accessory Cholera Enterotoxin (Ace) of Vibrio cholerae.

Chatterjee T, Sheikh IA, Chakravarty D, Chakrabarti P, Sarkar P, Saha T, Chakrabarti MK, Hoque KM - PLoS ONE (2015)

(A) Quenching of tryptophan fluorescence of Ace with CaCC inhibitors. (B) log [(Fo –Fc)/Fc] versus log [ligand] plot for the fluorescence quenching of Ace with CaCC inhibitors.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4634967&req=5

pone.0141283.g004: (A) Quenching of tryptophan fluorescence of Ace with CaCC inhibitors. (B) log [(Fo –Fc)/Fc] versus log [ligand] plot for the fluorescence quenching of Ace with CaCC inhibitors.
Mentions: Quenching of tryptophan fluorescence is frequently used to study protein-ligand interaction [29,30]. Addition of CaCC inhibitors resulted in quenching of tryptophan fluorescence of Ace. The quenching data are presented as a Stern-Volmer plot, showing F0/Fc versus concentration of small molecules (Fig 4A). A plot of log[(F0−Fc)/Fc].versus log([Q]) for Ace-small molecules interaction using least-squares analysis gave the binding constants (Fig 4B).

Bottom Line: Biophysical studies indicate that the unfolding (induced by urea) free energy increases upon binding CaCCinh-A01 and DGA, compared to native Ace, whereas binding of tannic acid destabilizes the protein.In contrast, binding to tannic acid had the opposite effect, indicating the loss of protein secondary structure.The efficacy of tannic acid in mouse model suggests that the targeted modulation of Ace structure may be of therapeutic benefit for gastrointestinal disorders.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Bose Institute, P1/12 CIT Scheme VIIM, Kolkata, 700054, India.

ABSTRACT
Cholera pathogenesis occurs due to synergistic pro-secretory effects of several toxins, such as cholera toxin (CTX) and Accessory cholera enterotoxin (Ace) secreted by Vibrio cholerae strains. Ace activates chloride channels stimulating chloride/bicarbonate transport that augments fluid secretion resulting in diarrhea. These channels have been targeted for drug development. However, lesser attention has been paid to the interaction of chloride channel modulators with bacterial toxins. Here we report the modulation of the structure/function of recombinant Ace by small molecule calcium-activated chloride channel (CaCC) inhibitors, namely CaCCinh-A01, digallic acid (DGA) and tannic acid. Biophysical studies indicate that the unfolding (induced by urea) free energy increases upon binding CaCCinh-A01 and DGA, compared to native Ace, whereas binding of tannic acid destabilizes the protein. Far-UV CD experiments revealed that the α-helical content of Ace-CaCCinh-A01 and Ace-DGA complexes increased relative to Ace. In contrast, binding to tannic acid had the opposite effect, indicating the loss of protein secondary structure. The modulation of Ace structure induced by CaCC inhibitors was also analyzed using docking and molecular dynamics (MD) simulation. Functional studies, performed using mouse ileal loops and Ussing chamber experiments, corroborate biophysical data, all pointing to the fact that tannic acid destabilizes Ace, inhibiting its function, whereas DGA stabilizes the toxin with enhanced fluid accumulation in mouse ileal loop. The efficacy of tannic acid in mouse model suggests that the targeted modulation of Ace structure may be of therapeutic benefit for gastrointestinal disorders.

No MeSH data available.


Related in: MedlinePlus