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A molecular model for the redox potential difference between thioredoxin and DsbA, based on electrostatics
P J Gane1, R B Freedman, J Warwicker
1Biological Laboratory, University of Kent Canterbury, UK.
Journal of Molecular Biology
|June 2, 1995
Summary
Structural differences in thioredoxin and DsbA proteins explain their distinct oxidizing strengths. Electrostatics calculations reveal how altered stabilization of reduced forms contributes to the significant redox potential difference between these homologous proteins.
Area of Science:
- Biochemistry
- Structural Biology
- Computational Biology
Background:
- Thioredoxin and DsbA proteins share homologous active sites but exhibit different oxidizing capabilities.
- DsbA is a significantly stronger oxidant than thioredoxin, with a measured redox potential difference of 160 mV.
Purpose of the Study:
- To investigate the molecular basis for the difference in redox potential between thioredoxin and DsbA.
- To elucidate how the relative stabilities of the reduced forms of these proteins contribute to their distinct oxidizing strengths.
Main Methods:
- Utilized electrostatics calculations to study the relative stabilities of the reduced forms of thioredoxin and DsbA.
- Developed a molecular model to explain differences in thiolate stabilization between the two proteins.
Main Results:
- Calculations suggest altered stabilization of exposed, ionized thiolates in the reduced forms accounts for much of the redox potential difference.
- Specific interactions like thiolate-NH35 (thioredoxin)/33 (DsbA) stabilize reduced forms, but differences arise from concerted action of multiple side-chain and main-chain groups.
- Residues H32 and Q97 in DsbA, along with polypeptide backbone regions and peptide dipoles near the active site, significantly contribute to thiolate stabilization and the redox potential difference.
Conclusions:
- The significant redox potential difference between DsbA and thioredoxin is primarily due to differences in the electrostatic stabilization of their reduced, thiolate forms.
- A combination of specific residue interactions, polypeptide backbone conformation, and the influence of an additional protein domain in DsbA collectively determines the differential stabilization.