Photosynthesis Helper Protein Discovered

The helper protein (blue) pulls on one end of Rubisco and frees up the sugar. The blockage is lifted. (Manajit Hayer-Hartl/Max Planck Institute for Biochemistry)
Photosynthesis is less efficient in plants than it could be. Red algae, in contrast, use a slightly different mechanism and are thus more productive. Scientists from Germany's Max Planck Institute of Biochemistry (MPIB) have now identified a helper protein for photosynthesis in red algae.

“We could elucidate its structure and its intriguing mechanism,” says Manajit Hayer-Hartl, MPIB group leader. “Comparing its mechanism to the one in green plants could help to design more efficient plants.”

Green plants, algae, and plankton metabolize carbon dioxide and water into oxygen and sugar in the presence of light. Without photosynthesis, life on earth would not be possible. The key protein of this process - Rubisco - is therefore one of the most important proteins in nature. It bonds with carbon dioxide and starts its conversion into sugar and oxygen.

"Despite its fundamental importance, Rubisco is an enzyme fraught with shortcomings," says Hayer-Hartl. One of the problems is that Rubisco binds to the wrong sugar molecules that inhibit its activity. The inhibitors have to be removed by a special helper protein, called Rubisco activase. The Max Planck scientists discovered that during evolution two different Rubisco activases developed in plants and in red algae. They differ in structure and in their working mechanism.

The newly discovered Rubisco activase in red algae repairs useless Rubisco proteins by pulling on one end of the protein. In doing so, the helper protein opens the active center of Rubisco and releases the inhibitory sugar. The respective Rubisco activase in green plants works by squeezing the inactive Rubisco protein and forcing it to let go of the sugar molecules. “Understanding the structure and function of the two activase helper proteins should facilitate efforts in biotechnology to generate plants and microorganisms that are able to convert more CO2 into valuable biomass than nature does,” says Hayer-Hartl.


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