Green plants, algae and plankton metabolize carbon dioxide (CO2) and water into oxygen and sugar in the presence of light. Without this process called photosynthesis, today's life on Earth would not be possible. The key protein of this process, called Rubisco, is thus 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 Manajit Hayer-Hartl, head of the Research Group "Chaperonin-assisted Protein Folding" at the MPIB.
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.
Two ways of restoring activity
The newly discovered Rubisco activase in red algae repairs useless Rubisco proteins by pulling on one end of the protein, like someone who opens a shoe string. In doing so, the helper protein opens the active centre of Rubisco and releases the inhibitory sugar. The respective Rubisco activase in green plants works more like an egg opener, 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," hopes Manajit Hayer-Hartl.
- Oliver Mueller-Cajar, Mathias Stotz, Petra Wendler, F. Ulrich Hartl, Andreas Bracher, Manajit Hayer-Hartl. Structure and function of the AAA+ protein CbbX, a red-type Rubisco activase. Nature, 2011; 479 (7372): 194 DOI: 10.1038/nature10568
- Mathias Stotz, Oliver Mueller-Cajar, Susanne Ciniawsky, Petra Wendler, F Ulrich Hartl, Andreas Bracher, Manajit Hayer-Hartl. Structure of green-type Rubisco activase from tobacco. Nature Structural & Molecular Biology, 2011; DOI: 10.1038/nsmb.2171
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