Plants capture the energy of the sun in the process of photosynthesis, but this is an inefficient process that limits their growth potential. Some bacteria have specialized structures (called carboxysomes) that increase their efficiency of photosynthesis, and if carboxysomes can be introduced into crop plants such as rice, wheat and soybeans it is anticipated that this would improve their growth and yield. The smaller the number of proteins that are needed to reconstitute functional carboxysomes, the easier it will be to succeed. The goal of this project is to combine the roles of two carboxysome proteins into one; in other words, one protein will play two essential roles by combining structural and enzymatic functions. It is proposed to develop two types of bi-functional carboxysome proteins: one that will help deliver carbon dioxide to the interior of the carboxysome, where it will be available to RUBISCO, a key enzyme of photosynthesis; the second will detoxify a molecule (2-phosphoglycolate) that is formed as an unwanted by-product of chemical reactions that compete with photosynthesis.
Broader Impacts: This project will provide interdisciplinary training in biochemistry, protein chemistry and synthetic biology to a postdoctoral fellow and to undergraduate students. In addition it will explore innovative approaches to the engineering of structures such as the carboxysome and has the potential to improve crop yields for both food and biofuel.
Bacterial microcompartments function as nano-factories within bacterial cells. The goal of this project was to modify the protein shells that surround the factories, so that they could carry out part of the function of whole structure. The project explored new ways to do this, combining methods in analysis and engineering of the constituent building blocks of the shell. Analysis involved looking at thousands of protein sequences, surveyed in sequenced microbial genomes, to identify possible (naturally occurring) architectures that might be suitable. These were then adapted into designs for several different types of Bacterial Microcompartments. Then undergraduate, graduate students and Postdoctoral Fellows produced the proteins and tested their functionality and their potential for incorporation into the shells of the Microcompartments. These experiments were done both in bacterial cells as well as in solution. By combining these results, we learned which about the nature of the shell itself, its sidedness—which side of the building blocks face outward and inward. Because Bacterial Microcompartments have potential to be engineered to manufacture compounds of interest (e.g. biofuels) the results of this study may have implications for efforts to develop bacterial cell factories to address important global problems. Likewise, by focusing on a Bacterial microcompartment involved in CO2 fixation, which converts CO2 into biologically useful compounds, our results can contribute to efforts to mitigate climate change. Because Bacterial Microcompartments like the carboxysome are the focus of intense research to develop them as metabolic modules for encapsulating other types of toxic or oxygen-sensitive chemistries (e.g. nitrogen fixation), these results will open a new frontier in versatility for microcompartment nano-engineering and synthetic biology.
