MSU researchers fabricate synthetic protein that streamlines carbon fixing machinery of cyanobacteria; potential boost for biofuels
Researchers at the MSU-DOE Plant Research Laboratory, Michigan State University, have fabricated a synthetic protein that not only improves the assembly of the carbon-fixing factory of cyanobacteria (also known as blue-green algae), but also provides a proof of concept for a device that could potentially improve plant photosynthesis or be used to install new metabolic pathways in bacteria.
The multi-function protein, which the researchers compare to a Swiss Army Knife, streamlines the molecular machinery of cyanobacteria, making biofuels and other green chemical production from these organisms more viable. The researchers describe their work in a paper in the journal The Plant Cell.
The multifunctional protein we’ve built can be compared to a Swiss Army knife. From known, existing parts, we’ve built a new protein that does several essential functions.—Raul Gonzalez-Esquer, MSU doctoral researcher and the paper’s lead author
Gonzalez-Esquer worked with Cheryl Kerfeld, the Hannah Distinguished Professor of Structural Bioengineering in the Michigan State University-DOE Plant Research Lab, and Tyler Shubitowski, MSU undergraduate student. Kerfeld’s lab studies bacterial microcompartments, or BMCs. BMCs are self-assembling organelles that sequester segments of biochemical pathways within a protein shell. These are self-assembling cellular organs that perform myriad metabolic functions—in a sense, they are molecular factories with many different pieces of machinery.
Given their functional diversity, BMCs constitute a rich source of metabolic modules for applications in synthetic biology.
The carboxysome, the cyanobacterial BMC for CO2 fixation, has attracted significant attention as a target for installation into chloroplasts and serves as the foundation for introducing other types of BMCs into plants. Carboxysome assembly involves a series of protein-protein interactions among at least six gene products to form a metabolic core, around which the shell assembles. This complexity creates significant challenges for the transfer, regulation, and assembly of carboxysomes, or any of the myriad of functionally distinct BMCs, into heterologous systems. To overcome this bottleneck, we constructed a chimeric protein in the cyanobacterium Synechococcus elongatus that structurally and functionally replaces four gene products required for carboxysome formation.—Gonzalez-Esquer et al.
The new protein replaces four gene products, yet still supports photosynthesis. Reducing the number of genes needed to build carboxysomes should facilitate the transfer of carboxysomes into plants.
This installation should help plants’ ability to fix carbon dioxide. Improving their capacity to remove CO2 from the atmosphere makes it a win-win, Gonzalez-Esquer said.
This proof of concept also shows that BMCs can be broken down to the sum of their parts, ones that can be exchanged. Since they are responsible for many diverse metabolic functions, BMCs have enormous potential for bioengineering, said Kerfeld, who also is an affiliate of the Berkeley National Laboratory’s Physical Biosciences Division.
We’ve showed that we can greatly simplify the construction of these factories. We can now potentially redesign other naturally occurring factories or dream up new ones for metabolic processes we’d like to install in bacteria.—Cheryl Kerfeld
However, while the improved organisms excel at photosynthesis in a lab setting, they’re ill-prepared to compete with other bacteria. Because they were stripped of four genes, they’re not as flexible as their natural cousins.
Cyanobacteria have adapted to live in ponds that are drenched by sun, blanketed by shade, frozen solid in the winter, not to mention the other organisms with which they have to compete to survive. We’ve restricted ours and their ability to grow; they no longer have all of the tools to compete, much less dominate, in the natural environment.—Cheryl Kerfeld
C. Raul Gonzalez-Esquer, Tyler B. Shubitowski, and Cheryl A. Kerfeld (2015) “Streamlined Construction of the Cyanobacterial CO2-Fixing Organelle via Protein Domain Fusions for Use in Plant Synthetic Biology” Plant Cell doi: 10.1105/tpc.15.00329