The most prevalent enzyme on earth is Rubisco, which serves as the primary biocatalyst in photosynthesis. One of the most important early photosynthetic adaptations has been understood by a group of Max Planck researchers by reconstructing billion-year-old enzymes.
Their findings not only shed light on how modern photosynthesis evolved, but also give fresh ideas for enhancing it.
Old Enzymes show photosynthesis changes the oxygen levels
An international team from the University of Singapore and the Max Planck Institute for Terrestrial Microbiology in Marburg, Germany, has now successfully recreated and examined billion-year-old enzymes in the lab, as per sciencedaily.
Rather than direct changes in the active center, the researchers discovered that in this molecular paleontology process, a completely new component enabled photosynthesis to adjust to rising levels of oxygen.
Rubisco is old. it first appeared in early metabolism perhaps four billion years before oxygen was present on Earth.
As oxygen levels in the atmosphere increased and oxygen-producing photosynthesis was developed, the enzyme began catalyzing an unintended reaction in which it mistook O2 for CO2 and created compounds that were harmful to cells.
It is still completely unknown what chemical factors contribute to Rubisco's higher CO2 specificity. However, those who are working to enhance photosynthesis are quite interested in them.
It's interesting to note that the Rubiscos with higher CO2 specificity acquired a brand-new protein component with an unidentified function.
Researchers from Nanyang Technological University in Singapore and the Max Planck Institute for Terrestrial Microbiology in Marburg used a statistical algorithm to recreate forms of Rubiscos that were present billions of years ago before oxygen levels started to rise, to understand this crucial event in the evolution of more specific Rubiscos.
The group, led by Max Planck researchers Tobias Erb and Georg Hochberg, revived these antiquated proteins in the lab to investigate their features.
The researchers specifically questioned if the new Rubisco component had anything to do with the development of increased specificity.
According to Max Planck Director Tobias Erb, the study also has significant ramifications for how photosynthesis might be enhanced.
Their research taught us that traditional attempts to enhance Rubisco have been looking in the wrong place for years, research solely focused on altering amino acids in Rubisco on its own to enhance it.
Their work now suggests that adding completely new protein components to the enzyme could be productive and may open previously impassable evolutionary pathways.
Read More: Scientists Want to Improve Photosynthesis, but is That a Good Idea?
Rubisco on Photorespiration
The act of absorbing molecular oxygen (O2) in response to light while simultaneously releasing carbon dioxide (CO2) from organic substances is known as photorespiration. In the reversal of photosynthesis, in which CO2 is fixed and O2 is released, the gas exchange is like respiration, as per BioOne.
Even though RUBISCO developed from sulfur metabolism-related enzymes over 3 billion years ago, it is still the enzyme responsible for a significant portion of net CO2 fixation from the environment.
Only one source of molecular oxygen in the atmosphere during RUBISCO development was likely UV light-induced photolysis of water, and levels were 10-14 below current levels.
This was accomplished so successfully by cyanobacteria, the ensuing algae, and especially land plants that O2 has overtaken CO2 as the second most prevalent gas in the atmosphere today.
The specificity of RUBISCO for CO2 has improved somewhat due to selection pressure, but further improvement may not be possible without reducing catalytic rates.
Related Article: Key Enzyme Found in Plants Could Guide Development of Medicines and Other Products
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