Origin and evolution of the mitochondrial proteome

Area of Science:

• Molecular Biology and Evolutionary Biology
• Cell Biology
• Genomics

Background:

• The prevailing endosymbiotic theory explains mitochondria's origin from an alpha-proteobacteria symbiont.
• Mitochondrial genomes have undergone significant reduction in size.
• Gene transfer from the endosymbiont to the host nucleus is a key process.

Purpose of the Study:

• To re-evaluate and propose modifications to the endosymbiotic theory of mitochondria.
• To elucidate the diverse origins of mitochondrial proteins.
• To investigate the evolutionary trajectory of mitochondrial function, particularly regarding respiration.

Main Methods:

• Phylogenetic analysis of mitochondrial and nuclear genomes.
• Comparative genomics to identify protein homology and evolutionary relationships.
• Reconstruction of ancestral genomic content and functional capabilities.

Main Results:

• Mitochondrial proteome originates from three sources: alpha-proteobacteria, non-homologous proteins, and other bacterial affinities.
• Gene loss and nuclear transfer significantly reduced mitochondrial genome size.
• Evidence suggests an aerobic, not anaerobic, initial function for ancestral mitochondria.

Conclusions:

• The endosymbiotic theory requires substantial modification based on proteomic and genomic data.
• Mitochondria have a continuous history of aerobic respiration, with early roles possibly involving oxygen scavenging.
• The ancestral host was likely a heterotroph, with no specific alpha-proteobacterial origin for glycolysis genes.