A fourth SOD enzyme shares its evolutionary heritage with MnSOD, but utilizes iron as its cofactor (FeSOD) 21.
Each has a unique 3D structure, amino acid sequence, and metal cofactor(s) either manganese (MnSOD), nickel (NiSOD), or a combination of copper and zinc (CuZnSOD) 19, 20. Phylogenetic methodologies coupled with protein structural analyses have revealed that three different isoforms of SOD enzymes evolved independently of one another to remove unnecessary O 2.
Perhaps, it is for this reason that SODs and SORs have been found in all three domains of life-Eukarya, Archaea, and Bacteria 14. − with damage caused by over-exposure, organisms must maintain control over their abundance. To balance the beneficial effects of O 2. − are allowed to accumulate inside the cell, they react with solvent-exposed 4Fe-4S clusters in proteins, including those required for amino acid biosynthesis 17 and photosynthesis 18, generating reactants of the Fenton reaction, which can ultimately lead to extensive DNA damage 12. They can also have beneficial roles in iron acquisition, cell signaling, and growth 15, 16, but if O 2. − are produced as a byproduct of photosynthetic and respiratory electron transport chains 12 as well as extracellular processes on the cell surface 15.
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Although peroxidases and catalases enhance the rate of removal of peroxides (such as H 2O 2 and R-O-O-H) 13, SORs and SODs remove superoxide free radicals (O 2. Therefore, it is reasonable to assume that O 2-generating organisms, such as cyanobacteria, would have co-evolved more efficient mechanisms of managing ROS as water oxidation proteins evolved.Ĭyanobacteria remove ROS using carotenoids, α-tocopherol, and antioxidant enzymes, including peroxidases, catalases, superoxide reductases (SORs), and superoxide dismutases (SODs) 12, and their evolutionary history can be elucidated with phylogenetic methodologies. Such effects have been documented in the photosynthetic machinery, which has been evolving strategies of dealing with reactive oxygen species (ROS) throughout its history 11. Since O 2 is highly reactive, early Cyanobacteria-the first producers of biogenic O 2-likely experienced selective pressure, resulting in the evolution of more efficient antioxidants. With the evolution of oxygenic photosynthesis came the potential to produce O 2 on a much larger scale. Before this, O 2 could have been produced by physical processes, such as photodissociation of water and carbon dioxide by UV light 9, 10, but is unlikely to have accumulated at appreciable levels. Just how and when O 2 first appeared as a byproduct of biological evolution-oxygenic photosynthesis - remains controversial, with estimates ranging from near the origin of life 4 to 3.8 billion years ago (Ga) 5 to immediately preceding the Great Oxidation Event (GOE) 6, which is estimated to have begun 2.50–2.45 Ga 7, 8. Although today the Earth’s atmosphere contains ~21% oxygen (O 2), it was at least 10 5 times lower in the Archaean 4.0–2.5 billion years ago (Gya) 2, 3. Oxygen is essential for complex life forms as it is used during aerobic respiration to create more energy per mol of substrate than other available electron acceptors 1. Our analyses of metalloenzymes dealing with reactive oxygen species (ROS) now demonstrate that marine geochemical records alone may not predict patterns of metal usage by phototrophs from freshwater and terrestrial habitats. The evolution of NiSOD is particularly intriguing because it corresponds with cyanobacteria’s invasion of the open ocean.
By the Paleoproterozoic, they became genetically capable of using iron, nickel, and manganese as cofactors (FeSOD, NiSOD, and MnSOD respectively). Shortly afterwards, we find phylogenetic evidence that ancestral cyanobacteria used SODs with copper and zinc cofactors (CuZnSOD) during the Archaean. Our Bayesian molecular clocks, calibrated with microfossils, predict that stem Cyanobacteria arose 3300–3600 million years ago. Here we investigate when superoxide dismutase enzymes (SODs) capable of removing superoxide free radicals evolved and estimate when Cyanobacteria originated.
The ancestors of cyanobacteria generated Earth’s first biogenic molecular oxygen, but how they dealt with oxidative stress remains unconstrained.
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