Melatonin: an ancient molecule that makes oxygen metabolically tolerable

Area of Science:

• Biochemistry
• Evolutionary Biology
• Cell Biology

Background:

• Melatonin exhibits diverse functions, including antioxidant and circadian regulation.
• Photosynthesis generates toxic free radicals, necessitating antioxidant defenses.
• Mitochondria and chloroplasts may retain ancestral melatonin synthesis pathways.

Purpose of the Study:

• To hypothesize the primary evolutionary role of melatonin as an antioxidant in early cyanobacteria.
• To explore the potential role of mitochondria and chloroplasts in melatonin synthesis in eukaryotes.
• To investigate the mechanisms by which melatonin mitigates oxidative stress.

Main Methods:

• Evolutionary hypothesis based on the timeline of cyanobacteria and photosynthesis.
• Comparative analysis of melatonin synthesis in prokaryotes and eukaryotes.
• Review of literature on melatonin's antioxidant mechanisms and cellular localization.

Main Results:

• Melatonin's initial function likely evolved as an antioxidant in ancient photosynthetic cyanobacteria.
• Mitochondria and chloroplasts are proposed as primary sites for melatonin synthesis in eukaryotes.
• Melatonin and its metabolites effectively scavenge reactive oxygen and nitrogen species and modulate related enzymes.

Conclusions:

• The primary evolutionary role of melatonin was antioxidant defense in early cyanobacteria.
• Endosymbiotic events likely led to the retention of melatonin synthesis in eukaryotic organelles.
• Melatonin employs multiple direct and indirect mechanisms to combat oxidative stress.