Location: Plant Genetics ResearchTitle: Cyanobacterial carboxysome mutant analysis reveals the influence of enzyme compartmentalization on cellular metabolism and metabolic network rigidity
|ABERNATHY, MARY - Washington University|
|CZAJKA, JEFFREY - Washington University|
|Allen, Douglas - Doug|
|HILL, NICHOLAS - University Of Colorado|
|CAMERON, JEFFREY - University Of Colorado|
|TANG, YINJIE - Washington University|
Submitted to: Metabolic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2019
Publication Date: 4/25/2019
Citation: Abernathy, M., Czajka, J., Allen, D.K., Hill, N.C., Cameron, J.C., Tang, Y.J. 2019. Cyanobacterial carboxysome mutant analysis reveals the influence of enzyme compartmentalization on cellular metabolism and metabolic network rigidity. Metabolic Engineering. 54:222-231. https://doi.org/10.1016/j.ymben.2019.04.010.
Interpretive Summary: Photosynthesis in 'green' systems is the source of renewable energy and food that sustain existence on the planet. Some plants and photosynthetic microbes have developed ways to more efficiently capture carbon dioxide and convert to the macromolecules such as protein, oil and carbohydrate that are the source of food and feed stocks. However, our understanding of the metabolism that underlies this more efficient form of photosynthesis is poor. Here we investigate a simple cyanobacterial system that has been mutated so it does not possess the efficient photosynthesis. Using isotopic tracers and analyses of flux our study provides important insights at the biochemical level about regulation of metabolism and how it might be engineered for enhanced productivity of the compounds we desire in plants that will result in cost effective renewable alternatives and more food in the future.
Technical Abstract: Cyanobacterial carboxysomes encapsulate carbonic anhydrase and ribulose-1,5-bisphosphate carboxylase/oxygenase and are key organelles for CO2 concentration and fixation. Genetic deletion of the major structural proteins encoded in the ccm operon in Synechococcus sp. PCC 7002 ('ccmKLMN) disrupts carboxysome formation and significantly affects cell physiology. In this study, we employed both metabolite pool size analysis and isotopically nonstationary metabolic flux analysis (INST-MFA) to examine metabolic regulation in cells lacking carboxysomes. The results indicate that the 'ccmKLMN mutant grows similar to wild type under high CO2 environments with a similar flux distribution through central metabolism except moderately elevated protein synthesis and photorespiration activity. At the level of metabolites, the 'ccmKLMN strain had larger pool sizes of pyruvate, UDPG, and aspartate and greater excretion of malate and succinate. Under photomixotrophic conditions, both wild type and the 'ccmKLMN mutant metabolized acetate and pyruvate. Provision of acetate could promote carboxysome mutant growth when light and CO2 were insufficient. The results suggest that the 'ccmKLMN mutant reorganizes flux minimally through more significant changes in intracellular metabolite pool concentrations. The removal of microcompartments may redirect central metabolites to competing pathways (e.g., lactate production). This study provides important insights into both metabolic regulation via enzyme compartmentation and the compensatory responses in cyanobacterial phototrophic metabolism.