Science Fiction Writer Arthur Clarke says: “Any sufficiently advanced technology is equivalent to magic”.These words are clear cut evidence on the profound discovery of artificial photosynthesis using Spinach Chloroplast. Nature amalgamates complex biosynthetic and energy converting tasks within compartments like chloroplast and mitochondria. Conversion of light energy into chemical form in chloroplast led to carbon dioxide fixation. Carbon dioxide, being an essential factor, development of efficient strategies are needed for the upcoming green economy.
Two major photosynthetic processes of plant chloroplast are light reactions and dark reactions. In the former, energy carrier Adenosine triphosphate is generated and reduces Nicotinamide dinucleotide phosphate(NADPH) whereas in the latter these molecules are used to fix carbon dioxide and thereby to build biomass.
CETCH cycle
As the technology had progressed, researchers built an artificial version of the chloroplast. It uses sunlight and a laboratory designed chemical pathway to turn carbon dioxide into sugar. Six pathways exist for the fixation of carbon dioxide naturally and it raised to seven by the discovery of Tobias Erb and his colleagues in 2016. The pathway was named CETCH (crotonyl-coenzyme A(CoA)/ethyl malonyl-CoA/hydroxybutyryl CoA ) Cycle and is a reaction network of 17 enzymes which converts carbon dioxide into organic molecules. The CETCH cycle was being drafted by metabolic retrosynthesis, established with enzymes originated from nine different organisms of all three domains of life which were optimised by enzyme engineering.
The CETCH cycle showed 20% more efficiency than natural pathways and scientist suspected whether it was compatible with the rest of living cell machinery. This led to the extraction of the chloroplast of spinach that showed a positive result. An artificial chloroplast was created, in which spinach chloroplast membranes intake solar energy before the synthetic CETCH cycle enzymes use that energy to break down Carbon dioxide. These enzymes convert Carbon dioxide into Glycolate molecule that can be used as a feedstock to produce useful organic products.
To reduce the limitations caused by natural chloroplast, researchers had a thought to construct chloroplast mimics which can be used as an energy production system for artificial cells. They also focussed on the modifications of artificial chloroplast with abilities like self-repair and self-reproduce like natural chloroplast can. For this Erb et al. collaborated with scientists at J.Craig Venter Institute in California who built tiny synthetic cells containing the minimal number of genes for life. This plan is to put CETCH cycle inside minimal cells which gives a new perspective for artificial chloroplast.
This is the high time to realise a synthetic metabolism that is more efficient in converting Carbon dioxide into biomass and in pharmaceuticals for the production of drugs which cannot be done by living cells. Tweaking can definitely reduce the harmful effects caused by carbon dioxide on earth. Let’s hope for a carbon-free environment through the development of this astonishing discovery.
-Ancy Anna Kurian
Ref: Nature, Science, Oxford Academic
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