Resurrecting billion-year-old enzymes reveals how photosynthesis adapted to the rise of oxygen

The central biocatalyst in photosynthesis, Rubisco, is the most abundant enzyme on earth. By reconstructing billion-year-old enzymes, a team of Max Planck Researchers has deciphered one of the key adaptations of early photosynthesis. Their results, now published in Science, not only provide insights into the evolution of modern photosynthesis but also offer new impulses for improving it.

Using a combination of computational and synthetic approaches, a team from the Max-Planck-Institute for Terrestrial Microbiology in Marburg, Germany in collaboration with the University of Singapore has now successfully resurrected and studied billion-year-old enzymes in the lab. In this process, which they describe as "molecular paleontology," the researchers found that instead of direct mutations in the active center, an entirely new component prepared photosynthesis to adapt to rising oxygen levels.

The molecular determinants of increased CO2 specificity in Rubisco remain largely unknown. However, they are of great interest to researchers aiming to improve photosynthesis. Interestingly, those Rubiscos that show increased CO2 specificity recruited a novel protein component of unknown function. This component was suspected to be involved in increasing CO2 specificity, however, the true reason for its emergence remained difficult to determine because it already evolved billions of years ago.

The answer was surprising, as doctoral researcher Luca Schulz explains: "We expected the new component to somehow directly exclude oxygen from Rubisco catalytic center. That is not what happened. Instead, this new subunit seems to act as a modulator for evolution: recruitment of the subunit changed the effect that subsequent mutations had 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."

Image source: MPI f. Terrestrial Microbiology/ L. Schulz.