Evolution of complex I-like respiratory complexes.

Area of Science:

• Biochemistry
• Evolutionary Biology
• Structural Biology

Background:

• Respiratory complex I, membrane-bound hydrogenase (MBH), and membrane-bound sulfane sulfur reductase (MBS) share a common ancestor.
• MBH and MBS utilized protons and sulfur as electron sinks, crucial for energy conservation in Earth's early, low-oxygen Proterozoic atmosphere.
• These enzymes likely evolved from a fusion of ancestral membrane transporters and soluble [NiFe] hydrogenase modules.

Purpose of the Study:

• To review the evolutionary relationships and catalytic mechanisms of respiratory complexes.
• To highlight how recent structural determinations advance our understanding of these ancient enzymes.
• To connect the structures of MBH, MBS, and complex I.

Main Methods:

• High-resolution cryo-electron microscopy (cryo-EM) was employed to determine the structures.
• Comparative analysis of determined structures of MBH, MBS, multiple resistance and pH antiporter, photosynthetic NADH dehydrogenase-like complex type-1, and complex I.
• Review of existing literature on the catalytic mechanisms and evolutionary origins.

Main Results:

• Recent cryo-EM structures have significantly clarified the catalytic mechanisms of MBH, MBS, and complex I.
• Structural data supports the proposed evolutionary link between these diverse membrane-bound enzyme complexes.
• The findings provide insights into the functional adaptations of these proteins over evolutionary time.

Conclusions:

• The structural and mechanistic insights gained from cryo-EM are revolutionizing our understanding of respiratory complex evolution.
• Complex I, MBH, and MBS represent a continuum of evolutionary adaptation from early life energy-conserving mechanisms.
• Further structural studies will continue to illuminate the intricate evolutionary history of bioenergetic pathways.