Structural basis of multifunctional bovine mitochondrial cytochrome bc1 complex

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• The mitochondrial cytochrome bc1 complex is a key enzyme in cellular respiration.
• It is involved in electron transfer, proton translocation, peptide processing, and superoxide generation.
• Understanding its structure-function relationship is crucial for comprehending cellular energy production and disease mechanisms.

Purpose of the Study:

• To elucidate the structural and functional significance of the iron-sulfur protein (ISP) head domain movement in the cytochrome bc1 complex.
• To investigate the mechanisms of peptide processing and superoxide generation within the complex.
• To correlate structural findings with catalytic activities and inhibitor effects.

Main Methods:

• X-ray crystallography at 2.9 A resolution to determine the complex's structure.
• Site-directed mutagenesis in Rhodobacter sphaeroides to analyze ISP neck rigidity.
• Kinetic analysis of electron transfer rates in native and inhibited beef heart complexes.
• Biochemical assays to study peptide-processing and superoxide generation activities.

Main Results:

• Crystal structure revealed redox centers, inhibitor binding sites, and suggested ISP head domain movement during catalysis.
• Mutant analysis confirmed the functional importance of ISP head domain mobility.
• Peptide-processing activity, localized to subunits I and II, is activated by detergents that inhibit electron transfer.
• Superoxide generation occurs at reduced bL and Q*-, dependent on membrane potential and cytochrome c.

Conclusions:

• The movement of the ISP head domain is critical for cytochrome bc1 complex catalysis and function.
• Peptide processing and electron transfer activities can be differentially regulated.
• The study provides insights into the multifactorial roles of the cytochrome bc1 complex in cellular processes.