Relationship between redox function and protein stability of cytochromes c

Area of Science:

• Biochemistry
• Biophysics
• Protein Science

Background:

• Cytochromes c are crucial electron transfer proteins involved in various biological processes.
• Understanding the factors regulating their redox potential is essential for deciphering their function.
• Protein stability plays a significant role in protein function, especially at varying temperatures.

Purpose of the Study:

• To investigate the relationship between protein stability and redox potential in mesophile Pseudomonas aeruginosa cytochrome c551 and thermophile Hydrogenobacter thermophilus cytochrome c552.
• To elucidate the contribution of enthalpic factors to the redox potential.
• To determine how the stability of the oxidized protein form influences the Fe-methionine coordination bond and redox function.

Main Methods:

• Electrochemical studies were performed on purified proteins and their mutants.
• Nuclear Magnetic Resonance (1H NMR) spectroscopy was utilized to assess protein structure and dynamics.
• Optical spectroscopy provided insights into electronic properties and redox states across a wide temperature range.

Main Results:

• Stable protein structures exhibited low redox potentials, primarily driven by enthalpic contributions to the redox reaction.
• The stability of the oxidized protein form was directly correlated with the stability of the critical Fe-methionine coordination bond.
• Mutational analysis revealed specific residues influencing protein stability and redox properties.

Conclusions:

• Protein stability is a key determinant of redox potential in cytochromes c, mediated by enthalpic factors.
• The Fe-methionine coordination bond's stability, regulated by the oxidized protein form's stability, directly controls the redox function.
• These findings provide fundamental insights into the structure-function relationships of cytochromes c.