Carboxysomes are polyhedral protein microcompartments found in many autotrophic bacteria. They are composed of a thin protein shell and are filled with 1,5-bisphosphate carboxylase/oxygenase (RubisCO). This research seeks answers to the question of the advantage these bacteria derive from packaging their carbon dioxide fixing enzyme (RubisCO) into carboxysomes. The PIs previously showed that a unique carbonic anhydrase (CA), which is tightly associated with the carboxysome shell, enhances RubisCO's catalytic efficiency by mediating what appears to be a directional transfer of abundant cytoplasmic bicarbonate to the carboxysome interior as carbon dioxide. The ability of the shell to impede diffusion of bicarbonate and carbon dioxide traps the gas in the interior, where it is fixed by RubisCO. Structural and molecular biological approaches will be combined with genetic and biochemical experiments to further elucidate structural and functional features of the microcompartment that will yield a deeper understanding of its role in microbial carbon metabolism.
Broader Impacts: Given the large contribution of carboxysome-containing organisms towards carbon dioxide fixation and the impact of their metabolism on the global carbon cycle, broader implications of the work planned will be the elucidation of one of the most basic and central biochemical processes that controls the carbon cycle and influence weather and climate.
Graduate and undergraduate students participating in the project will gain experience in biochemical and molecular biological research approaches. Through ongoing collaborations with scientists at this and other institutions, these students will gain an appreciation of interdisciplinary scientific approaches. The PIs will continue their practice of actively recruiting members of underrepresented groups (e.g. ethnic minorities and women) to participate in the project as undergraduate and graduate student researchers.
Carboxysomes are nano-scale polyhedral microcompartments that convert atmospheric carbon dioxide (CO2) to cellular material. Found in bacteria that make a large contribution towards global CO2 fixation and have a significant impact on the global carbon cycle, carboxysomes are central players in one of the most basic and central biochemical processes that control the carbon cycle and influence weather and global climate. Carboxysomes and related microcompartments also hold great promise as nanodevices for a variety of future biotechnological applications. We are working towards gaining an understanding of the role carboxysomes play in bacterial carbon metabolism by determining the contributions of their structure to their function and have made progress in understanding the path that leads to the assembly of a carboxysome in the bacterial cell itself and under defined conditions in the laboratory. Of importance for the design of carboxysome-based nanodevices is the insight our work has revealed into the permeability of the thin protein layer that surrounds the carboxysome interior to different chemical entities. Our success in directing a foreign protein into the carboxysome interior serves as proof-of-concept that carboxysomes can be "engineered" to contain proteins that are unrelated to their function. Several graduate and undergraduate students participated in the project and gained experience in carboxysome research. Through ongoing collaborations with scientists at this and other institutions, these students gained an appreciation of multi-disciplinary research approaches. Furthermore, the bacterial growth and carboxysome production facility in the PIs’ lab serves as the main source of purified carboxysome samples and research material for other scientists.
