Bristol team develops photosynthetic proteins for expanded solar energy conversion

A team of scientists from the University of Bristol, has developed a new photosynthetic protein system that enable an enhanced and more sustainable approach to solar-powered technological devices. This is the first time, the scientists were able to build a single protein system that uses both chlorophyll and bacteriochlorophyll, and in doing so have demonstrated the two pigment systems can work together to achieve solar energy conversion.

The initiative is part of a broader effort in the field of synthetic biology because using proteins in place of man-made materials are expensive and can be harmful to the environment when the device becomes obsolete.

The aim of the study was the development of "chimera" photosynthetic complexes that display poly-chromatic solar energy harvesting. According to the statement issued by Dr Mike Jones, Lead author of the study and Reader in Biochemistry at the University of Bristol:

"We have assembled these two proteins, from very different parts of the photosynthetic world, into a single biological photosystem that enables expanded solar energy harvesting. We have also demonstrated that this system can be interfaced with man-made electrodes to achieve expanded solar-to-electric conversion."

"In the past, two main types of protein have been used for solar energy conversion in technological devices. The first are from 'oxygenic' photosynthetic organisms -plants, algae and cyanobacteria - that contain chlorophyll as their main photosynthetic pigment and produce oxygen as a waste product of the process. The second are from 'anoxygenic' organisms, bacteria that contain bacteriochlorophyll as their primary photosynthetic pigment.

In collaboration with photo electrochemistry colleagues at the Free University Amsterdam, the scientists from the University's BrisSynBio Institute, purified a 'reaction centre' protein from a purple-coloured photosynthetic bacterium and a light-harvesting protein from a green plant (actually made recombinantly in E. coli) and locked them permanently together using a linking domain taken from a second bacterium.

The result is the first single complex with a well-defined protein and pigment composition that shows expanded solar energy conversion.

The BBSRC and EPSRC-funded study, the breakthrough, is an example of a synthetic biology approach, treating proteins as components that can be assembled in new and interesting ways using a common and predictable interface.

"This work shows that it is possible to diversify the protein systems which can be built into devices beyond those which nature supplies, using a simple approach achieved purely through genetic encoding," said Dr Jones.

In the next step, they are expanding the palette of photosynthetic pigments, using proteins from cyanobacteria containing bilin pigments that absorb yellow and orange light, and exploring linking enzymes to these novel photosystems in order to use sunlight to power catalysis.