Interactions between yeast iso-1-cytochrome c and its peroxidase

Area of Science:

• Biochemistry
• Structural Biology
• Protein-protein interactions

Background:

• Yeast iso-1-ferricytochrome c (Cc) and ferricytochrome c peroxidase (CcP) form essential complexes.
• Understanding these interactions is key to deciphering electron transfer mechanisms.

Purpose of the Study:

• To investigate the thermodynamic and structural basis of Cc-CcP complex formation.
• To probe the role of specific residues and nonpolar interactions at the protein interface.

Main Methods:

• Isothermal titration calorimetry (ITC) was employed to study 19 different Cc-CcP complexes.
• Site-directed mutagenesis was used to create CcP and Cc variants.
• Double-mutant cycles were utilized to assess residue coupling energies.

Main Results:

• High-affinity binding sites for Cc and CcP were confirmed to be at the crystallographically defined interface.
• Substitution of charged residues with alanine increased binding enthalpy but affected stability based on location.
• Deletion of methyl groups impacted binding enthalpy and free energy, highlighting the role of hydrophobic interactions.
• Analysis of residue pairs indicated that many substitutions induce complex rearrangements.

Conclusions:

• The study confirms the importance of the defined interface and nonpolar interactions in stabilizing Cc-CcP complexes.
• Protein interface mutations can lead to significant structural rearrangements within the complex.
• Thermodynamic and structural data provide insights into the molecular mechanisms governing Cc-CcP interactions.