Thermodynamic identification of stable folding intermediates in the B-subunit of cholera toxin.


The structural stability and domain structure of the pentameric B-subunit of cholera toxin have been measured as a function of different perturbants in order to assess the magnitude of the interactions within the B-subunits. For these studies, temperature, guanidine hydrochloride (GuHCl), and pH were used as perturbants, and the effects were measured by high-sensitivity differential scanning calorimetry, isothermal reaction calorimetry, fluorescence spectroscopy, and partial protease digestion. At pH 7.5 and in the absence of any additional perturbants, the thermal unfolding of the B-subunit pentamer is characterized by a single peak in the heat capacity function centered at 77 degrees C and characterized by a delta Hcal of 328 kcal/mol of B-subunit pentamer and delta Hvh/delta Hcal of 0.3. Lowering the pH down to 4 or adding GuHCl up to 2 M results in a decrease of the calorimetric enthalpy with no significant effect on the van't Hoff enthalpy. The transition enthalpy decreases in a sigmoidal fashion with pH, with an inflection point centered at pH 5.3. Isothermal titration calorimetric studies as a function of pH also report a transition centered at pH 5.3 and characterized by an enthalpy change of 27 kcal/mol of B-subunit pentamer at 27 degrees C. Below this pH, the enthalpy change for the unfolding transition is reduced to approximately 100 kcal/mol of B-subunit pentamer. Similar behavior is obtained with GuHCl. In this case, a first transition is observed at 0.5 M GuHCl and a second one at 3 M GuHCl.(ABSTRACT TRUNCATED AT 250 WORDS) Study holds ProTherm entries: 4382, 4383, 4384, 4385, 4386 Extra Details: NaN3(3 mM) was added in the experiment structural stability; unfolding transition; cooperative;,pentameric ring

Submission Details

ID: vij3APEQ

Submitter: Connie Wang

Submission Date: April 24, 2018, 8:25 p.m.

Version: 1

Publication Details
Bhakuni V;Xie D;Freire E,Biochemistry (1991) Thermodynamic identification of stable folding intermediates in the B-subunit of cholera toxin. PMID:2036374
Additional Information

Structure view and single mutant data analysis

Study data

No weblogo for data of varying length.
Colors: D E R H K S T N Q A V I L M F Y W C G P

Data Distribution

Studies with similar sequences (approximate matches)

Correlation with other assays (exact sequence matches)

Relevant UniProtKB Entries

Percent Identity Matching Chains Protein Accession Entry Name
100.0 Type II secretion system protein E P37093 GSPE_VIBCH
97.1 Cholera enterotoxin subunit B P01556 CHTB_VIBCH