The effect of methylation on cytochrome c fragment complementation

Area of Science:

• Biochemistry
• Protein Chemistry
• Spectroscopy

Background:

• Cytochrome c is a vital protein in cellular respiration.
• Heme modification can influence protein function and structure.
• Understanding heme-protein interactions is crucial for elucidating electron transfer mechanisms.

Purpose of the Study:

• To investigate the impact of methylating heme propionates on the properties of a horse heart cytochrome c peptide.
• To compare the binding kinetics, stability, and catalytic activity of methylated and unmethylated heme peptides.

Main Methods:

• Chemical methylation of heme propionates in heme peptide 1-25 using acidified methanol.
• Kinetic analysis of the reassociation of methylated and unmethylated heme peptides with apocytochrome c.
• Spectroscopic techniques including fluorescence quenching and far-ultraviolet dichroism.
• Differential scanning calorimetry to determine melting temperature (Tm).
• UV-Vis spectroscopy to analyze charge transfer bands.

Main Results:

• Methylated heme peptide 1-25 reassociated with apocytochrome c with similar kinetics and dissociation constants compared to the unmethylated peptide.
• Similar fluorescence quenching, far-UV dichroic spectra, and catalytic activities were observed for both methylated and unmethylated complexes.
• The methylated complex exhibited a lower melting temperature (Tm) by approximately 10°C.
• A shift in the charge transfer band was observed for the methylated complex (720 nm) compared to the unmethylated complex (695 nm).

Conclusions:

• Methylation of the outer heme propionate results in minimal steric hindrance, causing subtle alterations in the methionine 80 ligation geometry.
• These minor structural changes affect thermal stability and spectral properties without significantly compromising binding affinity or catalytic function.