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Enhancing Photosynthesis By Repairing Rubisco

Enhancing Photosynthesis by repairing Rubisco

Manajit Hayer-Hartl heads the “Chaperonin-assisted Protein Folding” research group. Manajit has a long-standing interest in Rubisco, which is the central enzyme involved in photosynthesis. Her team has already reported many of the interacting partners involved in the assemble and folding of Rubisco. This current study is about the working principle of Rubisco activase.  As the name suggests, this enzyme plays a key role in the repairing of Rubisco once the enzyme loses its activity. The research detail is published in the journal Cell.

The assimilation of atmospheric CO2 is catalyzed by the enzyme Rubisco and converted to organic matter. Sugar molecules are generated from this central step of photosynthesis, and the sugar molecules from this step are used for the production of essentially all biomass. Despite the pivotal work of Rubisco, it works slowly and easily inhibited under the influence of sugar products. Hayer-Hartl hopes to boost the photosynthesis process by enhancing the function of Rubisco. Hayer-Hartl aims to address the growing demand for food with the growing population and also to reduce climate change due to the emission of greenhouse gases.

Repairing the photosynthetic enzyme Rubisco
An artistic interpretation of the mechanism of Rubisco activase in photosynthesis. Artwork: Julia Kuhl; Image Credit: Manajit Hayer-Hartl MPI of Biochemistry

Plants, algae, and certain cyanobacteria contain the enzyme Rubisco activase, Rca. The Rca enzyme is a ring-shaped complex, and it consists of six subunits with a pore in its center. The interaction between the inhibited Rubisco and Rca and how the sugar bound to the active site pocket is released, restoring the CO2 fixing activity of the enzyme, was not clear until now. Hayer-Hartl & colleagues used biochemistry, crystallography, and cryo-electron microscopy to decipher cyanobacterial Rca’s molecular mechanism.

The team discovered how Rca opens the active site pocket in Rubisco. The N-terminal of Rubisco is captured by Rca, and by pulling and pushing movement with the energy derived from ATP, Rca opens the active pocket site. Inhibitory sugar molecules are released at the end of this process. Rubisco is packed into specialized micro-compartments in cyanobacteria. These compartments, called carboxysomes, generate CO2 in high concentration, which facilitates the function of Rubisco.

Hayer-Hartl previously showed how Rubisco interacts with the SSUL domains of the scaffolding protein CcmM and how this interaction results in the recruitment of Rubisco into carboxysomes. Interestingly, the team now discovered that the recruitment of Rca occurs by a similar process. There are SSUL domains in the Rca hexamer that dock onto Rubisco during the formation of carboxysome. This ensures the presence of enough Rca inside the carboxysome and that it performs the functions essential for its repair. Thus, Rca plays a role in the activation of Rubisco and also mediates its recruitment into carboxysomes.

Manajit Hayer-Hartl concluded by stating Rca is absolutely important for the optimal function of Rubisco. The discovered mechanism of Rca, along with its dual function in cyanobacteria, will help the researchers to make photosynthesis more effective in the future. She adds that the team hopes that their discovery will lead them closer to their ultimate goal of increasing agricultural productivity.

Source

Enhancing Photosynthesis by repairing Rubisco.

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