August 05, 2020

The mechanism of catalysis and regulation of photosynthesis Calvin cycle revealed by biophysics

[ Instrument R & D of Instrument Network ] Photosynthesis is divided into two stages: photoreaction and Calvin cycle (dark reaction). The Calvin cycle includes a multi-step enzymatic reaction, which uses ATP and NADPH generated during the photoreaction process to fix carbon dioxide to generate carbon water Compound. So although the Calvin cycle does not require light energy, the process is still controlled by light / dark. In the light reaction stage, the light signal is finally converted into a redox signal through a series of proteins, and the Calvin cycle and a large number of downstream reactions are regulated by thioredoxin (TRX). Chloroplast phosphate ribulose kinase (PRK) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) are the key enzymes of the Calvin cycle. They consume ATP and NADPH produced during the photoreaction process, respectively, and are regulated by TRX redox. , When it is in the reduced state, it is activated, and when it is in the oxidized state, it is inactivated. In addition, CP12, another protein in the chloroplast, is also regulated by TRX and can interact with PRK and GAPDH in the oxidized state to form GAPDH / CP12 / PRK complexes. After the complex is formed, the activity of both enzymes is further inhibited.
On May 8, the International Plant Research Journal THE PLANT CELL published the research results of the Li Mei / Chang Wenrui Group of the Institute of Biophysics, Chinese Academy of Sciences, entitled Photosynthetic Phosphoribulokinase Structures: Enzymatic Mechanisms and the Redox Regulation of the Calvin-Benson-Bassham Cycle reveals the catalytic reaction mechanism of PRK in the Calvin cycle (dark reaction) of photosynthesis, and provides a structural basis for the mechanism of the Calvin cycle controlled by light / dark.
In this work, the researchers analyzed the crystal structure of PRK and its complexes, including the crystal structure of PRK derived from cyanobacteria combined with cofactor adenosine diphosphate (ADP) and glucose-6-phosphate (G6P), which are in oxidation The crystal structure of the Arabidopsis thaliana PRK and its reduced state, and the crystal structure of the GAPDH / CP12 / PRK complex formed by the Arabidopsis thaliana PRK and GAPDH and CP12. Based on the structural information, combined with the results of mutant liveness and affinity experiments, the active site of PRK, the key domains and amino acids involved in catalysis were determined, the molecular mechanism of PRK regulation by redox was explained, and the GAPDH / CP12 / PRK complex was displayed The specific details of the interactions between the proteins in the paper and revealed the mechanism of action of CP12 in regulating PRK and GAPDH activities in response to redox signals. These results provide important structural information for a deeper understanding of the catalytic mechanism of PRK and the fine regulation of the Calvin cycle.
Li Mei, a researcher of the Institute of Biophysics, is the corresponding author of the thesis. Ph.D students Yu Ailing and Dr. Xie Yuan are co-first authors of the work. The research work was jointly funded by the Ministry of Science and Technology's Key R & D Program, the Chinese Academy of Sciences Class B Pilot Project, the Chinese Academy of Sciences' Frontier Science Key Research Project, and the National Natural Science Foundation of China. Data collection and sample analysis are supported and assisted by relevant staff such as Shanghai Light Source and the Protein Science Research Platform of the Institute of Biophysics.

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