Evolution of the cytochrome c oxidase proton pump

Area of Science:

• Biochemistry
• Evolutionary Biology
• Molecular Biology

Background:

• Quinol and cytochrome c terminal oxidase complexes share homologous subunits with conserved histidines and heme-copper centers.
• The role of the CuA center and proton translocation mechanisms in these complexes are debated.
• Recent studies challenge the view of CuA as solely an electron conduit and suggest alternative proton translocation mechanisms.

Purpose of the Study:

• To explore the evolutionary relationship between quinol oxidase, cytochrome bc1, and cytochrome c oxidase complexes.
• To propose an evolutionary tree based on increasing respiratory complexity and efficiency.
• To investigate the origins of oxygenic respiration relative to other biological processes.

Main Methods:

• Comparative analysis of structural similarities in oxidase complexes.
• Review of experimental evidence on ubiquinone binding sites and proton translocation.
• Construction of an evolutionary tree based on functional complexity.

Main Results:

• Evidence supports a Q(H2)-loop mechanism or alternative proton translocation in some terminal oxidases.
• The Escherichia coli cytochrome bo3 complex exhibits dynamic ubiquinone binding sites.
• An evolutionary model suggests a primitive quinol oxidase diverged into cytochrome bc1 and cytochrome c oxidase complexes.

Conclusions:

• Oxygenic respiration is an ancient process, predating nitrogenic respiration and reaction-center photosynthesis.
• The evolution of respiratory complexity likely involved the divergence of a primitive quinol oxidase.
• Proton translocation mechanisms may vary across different terminal oxidase superfamilies.