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Decoding photosynthesis

Source: SeaWiFS Project et al., Public Domain

Photosynthesis is the process where plants use the energy of the sun to convert carbon dioxide and water into glucose. Scientists have been trying for years to imitate this process, the only difference being that they want to obtain electricity rather than glucose. So far, they have made some notable progress in this area, even if their achievements have yet to find application in large-scale energy production.

Now (2020), scientists at Berkeley Laboratory have managed to uncover what molecular mechanisms lie behind the water splitting reaction of photosynthesis, using a combination of nanoscale imaging and chemical analysis. To get a better understanding of the process the scientists analysed photosynthetic proteins using X-ray crystallography as well as X-ray emission spectroscopy, which they had already developed in 2018. This dual approach enabled them to gain chemical and protein structure information from the same sample at the same time. The imaging was performed with an X-ray free-electron laser (XFEL).

This new method made it possible to investigate how the entire protein structure changed while the X-ray free electron laser produced short bursts of X-rays. This allowed the scientists not only to analyse the protein at room temperature, but also capture various moments over the reaction time scale. Taking multiple snapshots in time also made it possible to get an idea of how one state went to the other as well as the cause and effect and the role that each atom played in this transition.

Scientists have long sought to emulate nature and harness the energy produced during the process of artificial synthesis. In 2015, a fully biomimetic leaf-like device for hydrogen production was developed which enabled a microalgae culture to be simultaneously hydrated with media and harvested from the hydrogen produced in a continuous flow regime, without needing to replace the algal culture. It generated hydrogen by direct photolysis of water resulting from redirecting the photosynthetic pathways in immobilised microalgae due to the lack of oxygen. This research was the first successful attempt to produce hydrogen in a continuous manner from microalgae culture.

In 2019, scientists built artificial cells as models of primitive cells. The used components that were able to supply energy to drive gene expression inside a microcompartment which generated energy that helped synthesize parts of the cells themselves. They combined a cell-free protein synthesis system, which consisted of various biological macromolecules gained from living cells, and small protein-lipids aggregates called proteoliposomes, which contained the proteins ATP synthase and bacteriorhodopsin, inside giant synthetic vesicles. The photosynthesized ATP was used as a substrate for the process by which messenger RNA (mRNA) was produced from DNA and as an energy for translation. By also including the genes for parts of the ATP synthase and the light-harvesting bacteriorhodopsin these processes were also employed to increase the synthesis of more bacteriorhodopsin and the constituent proteins of ATP synthase. The newly formed bacteriorhodopsin and ATP synthase parts then spontaneously integrated into the artificial photosynthetic organelles and further enhanced ATP photosynthesis activity.

These new insights into the mechanisms at work during photosynthesis have great implications for future energy production: the scientists are convinced that if they can fully understand, and as a consequence reproduce natural photosynthesis, it would enable them to use the design principles for building artificial photosynthetic systems that generate clean and renewable energy from sunlight and water.

Although much progress has been made in understanding the principles of the photosynthetic reaction, at least regarding technology and computational analyses, more research will have to be carried out to get a better understanding of how the reaction is completed and the enzyme is ready for the next cycle.