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Research finds how photosynthesis process adapted to rise of oxygen

ANI | Updated: Oct 22, 2022 23:58 IST

Munich [Germany], October 22 (ANI): The most prevalent enzyme on earth is Rubisco, which serves as the primary biocatalyst in photosynthesis, suggests a recent study.
One of the key adaptations of early photosynthesis 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.
Today's existence is entirely dependent on CO2 being captured and converted by photosynthetic creatures like plants and algae. An enzyme known as Rubisco, which yearly absorbs more than 400 billion tonnes of CO2, is at the centre of these operations. Rubisco had to continuously adjust to shifting environmental circumstances in order to take on such a significant position in the global carbon cycle.
A team from the Max Planck Institute for Terrestrial Microbiology in Marburg, Germany, in partnership with the University of Singapore, has now successfully revived and investigated billion-year-old enzymes in the lab using a combination of computational and synthetic methods. The researchers discovered that in this process, which they refer to as "molecular palaeontology," a completely new component prepared photosynthesis to adapt to increased oxygen levels rather than direct mutations in the active centre.
Rubisco's early confusion
Rubisco is very old; it first appeared in the early metabolism, around 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 catalysing an unintended reaction in which it mistook O2 for CO2 and created compounds that were harmful to cells. This unclear substrate scope continues to harm Rubiscos today and reduces photosynthetic productivity. Even while CO2 specificity increased through time in rubiscos that evolved in oxygen-rich settings, none of them was able to entirely eliminate the oxygen capture response.
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 recruited a brand-new protein component with an unidentified function. Although it was hypothesised that this component was responsible for raising CO2 specificity, it was difficult to ascertain the real cause of its origin because it had already evolved over a period of billions of years.

Studying evolution by resurrecting ancient proteins in the lab
Researchers from the Max Planck Institute for Terrestrial Microbiology in Marburg and Nanyang Technological University in Singapore used a statistical algorithm to recreate forms of Rubiscos that existed billions of years ago, before oxygen levels started to rise, in order to understand this crucial event in the evolution of more specific Rubiscos. Tobias Erb and Georg Hochberg's team at Max Planck revived these antiquated proteins in the lab to investigate their properties. The researchers specifically questioned if the emergence of increased specificity had anything to do with Rubisco's new component.
The answer was surprising, as doctoral researcher Luca Schulz explains: "We expected the new component to somehow directly exclude oxygen from Rubisco catalytic centre. That is not what happened. Instead, this new subunit seems to act as a modulator for evolution: recruitment of the subunit changed the effect of subsequent mutations on Rubisco's catalytic subunit. Previously inconsequential mutations suddenly had a huge effect on specificity when this new component was present. It seems that having this new subunit completely changed Rubisco's evolutionary potential."
An enzyme's addiction to its new subunit
This function as an "evolutionary modulator" also explains another mysterious aspect of the new protein component: Rubiscos that incorporated it is completely dependent on it, even though other forms of Rubisco can function perfectly well without it. The same modulating effect explains why: When bound to this small protein component, Rubisco become tolerant to mutations that would otherwise be catastrophically detrimental. With the accumulation of such mutations, Rubisco effectively became addicted to its new subunit.
The findings collectively provide an explanation for why Rubisco has retained this novel protein component ever since it was discovered. Georg Hochberg, the head of the Max Planck Research Group, explains: "The fact that this connection was just recently discovered emphasises how crucial evolutionary analysis is for comprehending the biochemistry that powers the world around us. We can learn so much about why biomolecules like Rubisco are the way they are today by studying their past. Furthermore, we still know very little about the evolutionary history of many biological phenomena. Being an evolutionary biochemist at this time is therefore incredibly interesting because nearly the complete molecular history of the cell has not yet been uncovered."
Scientific journeys back in time can provide invaluable insights for the future
According to Max Planck Director Tobias Erb, the study also has significant implications for how photosynthesis may be enhanced. "Our research showed us that previous attempts to enhance Rubisco may have been looking in the incorrect area. For many years, research was confined to altering the amino acids within Rubisco itself. Our research indicates that modifying the enzyme with whole new protein parts might be more beneficial and open up previously impassable evolutionary pathways. The field of enzyme engineering is unexplored here." (ANI)