Plants form molecular reaction vessels during photosynthesis

Photosynthesis is a natural phenomenon that has fascinated scientists for centuries. It is the process by which plants and other photosynthetic organisms generate organic fuel from the sun’s light. Through a complex chain of chemical reactions, light is converted into carbohydrates which can then be metabolised by the plant to grow. These carbohydrates are also consumed by other animals making them the foundation of most food webs.

We have come to rely on carbohydrates from plants more and more as they have applications in biofuel, food security and natural materials. Understanding the process of photosynthesis can help us get closer to generating sustainable energy from light.

The study of photosynthesis has come a long way. For example, scientists now know all of the enzymes involved in the process and have been able to successfully clone them into the bacterium Escherichia coli. Being able to do this is a critical step for synthetic biologists who want to harness photosynthesis for new applications.

However, despite the fact that much progress has been made, there is still a lot that we don’t know about photosynthesis. These knowledge gaps make it difficult to truly harness photosynthesis in research and emerging technologies.

A key question in the photosynthetic pathway revolves around the biosynthesis of chlorophyll, the green pigment that underpins photosynthesis. In order for chlorophyll to be synthesised, magnesium has to be inserted into a molecule called porphyrin. We know from studies in chemistry that this reaction is energetically very demanding. If it was to be done synthetically, it would require anhydrous and oxygen free environments with high temperatures and long reaction times. This is in stark contrasts to what we see in nature, where magnesium is inserted into porphyrin at low temperatures and in aqueous solvents. It was also not clear how plants produce enough energy to catalyse the reaction.  

A team of researchers set out to understand this process by using a combination of X-ray crystallography, in silico modelling of ligand binding and rational mutagenesis. The scientists collected structural data from an important enzymatic subunit called Ch1H using Diamond’s Macromolecular Crystallography beamlines. 

The results of their work were recently published in Nature Plants. They showed how the enzyme can sequester porphyrin away from solvents creating a closed reaction vessel within the protein. This closed vessel can then control the location of water molecules around the active site of the enzyme. The enclosure is produced by the intricate movement of different protein subunits, which was demonstrated by the research team at Diamond. The reaction vessel was shown to be extremely intricate with buried channels for the introduction of magnesium at the right moment. 

This is an important study showing the mechanisms behind nature’s incredible ability to generate energy and grow using the sun’s rays. The findings have uncovered an additional layer of intricacy and complexity in one of nature’s most fascinating phenomena. What is more, scientists knew how to perform chemical reactions that could insert magnesium into porphyrin however, these require lots of energy. Now, thanks to this study, we know about nature’s elegant solution to the problem, which can help to direct scientific discovery going forward.

The study is a stark reminder of how much is still to be discovered in processes that we already know a lot about. Even though we have been able to clone all of the enzymes in the photosynthetic pathway, we still lack a lot of mechanistic detail. However, once as we uncover the details, the findings can be directly applied to current research and technology to improve many global challenges, from food security to solar panels.

To find out more about the Macromolecular Crystallography (MX) group at Diamond, or to discuss potential applications, please contact MX Science Group Leader, Dave Hall: david.hall@diamond.ac.uk