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


Abstract

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 PDB Entries

Structure ID Release Date Resolution Structure Title
1P9R 2003-05-12T00:00:00+0000 2.5 Crystal Structure of Vibrio cholerae putative NTPase EpsE
1P9W 2003-05-12T00:00:00+0000 2.7 Crystal Structure of Vibrio cholerae putative NTPase EpsE
2BH1 2005-01-06T00:00:00+0000 2.4 X-ray structure of the general secretion pathway complex of the N- terminal domain of EpsE and the cytosolic domain of EpsL of Vibrio cholerae
4KSR 2013-05-17T00:00:00+0000 4.2 Crystal Structure of the Vibrio cholerae ATPase GspE Hexamer
4KSS 2013-05-17T00:00:00+0000 7.58 Crystal Structure of Vibrio cholerae ATPase GspsE Hexamer
1CHP 1995-02-15T00:00:00+0000 2.0 SURPRISING LEADS FOR A CHOLERA TOXIN RECEPTOR BINDING ANTAGONIST; CRYSTALLOGRAPHIC STUDIES OF CTB MUTANTS
1CHQ 1995-02-15T00:00:00+0000 2.1 SURPRISING LEADS FOR A CHOLERA TOXIN RECEPTOR BINDING ANTAGONIST; CRYSTALLOGRAPHIC STUDIES OF CTB MUTANTS
1CT1 1997-06-03T00:00:00+0000 2.3 CHOLERA TOXIN B-PENTAMER MUTANT G33R BOUND TO RECEPTOR PENTASACCHARIDE
1FGB 1996-02-21T00:00:00+0000 2.4 TOXIN
1G8Z 2000-11-21T00:00:00+0000 2.0 HIS57ALA MUTANT OF CHOLERA TOXIN B-PENATMER

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