Advances in the bacterial organelles for CO2 fixation

CO2-concentrating mechanisms (CCMs) provide a means for accumulating CO2 around Rubisco to overcome the inherent limitations of Rubisco and enhance CO2 fixation. Carboxysomes are proteinaceous organelles in cyanobacteria and some proteobacteria which serve as the central CO2-fixing factory of CCMs. Carboxysomes sequester the cellular Rubisco and carbonic anhydrase from the cytoplasm, using a selectively permeable shell that structurally resembles virus capsids. Great efforts have been made recently to advance our understanding of the molecular mechanisms underlying carboxysome structure, assembly, biogenesis, and physiology. Advances in fundamental knowledge about carboxysome assembly and function has stimulated rational design and engineering of the protein organelles for improving CO2 fixation and new functions. Carboxysomes are a family of bacterial microcompartments (BMCs), present in all cyanobacteria and some proteobacteria, which encapsulate the primary CO2-fixing enzyme, Rubisco, within a virus-like polyhedral protein shell. Carboxysomes provide significantly elevated levels of CO2 around Rubisco to maximize carboxylation and reduce wasteful photorespiration, thus functioning as the central CO2-fixation organelles of bacterial CO2-concentration mechanisms. Their intriguing architectural features allow carboxysomes to make a vast contribution to carbon assimilation on a global scale. In this review, we discuss recent research progress that provides new insights into the mechanisms of how carboxysomes are assembled and functionally maintained in bacteria and recent advances in synthetic biology to repurpose the metabolic module in diverse applications. Carboxysomes are a family of bacterial microcompartments (BMCs), present in all cyanobacteria and some proteobacteria, which encapsulate the primary CO2-fixing enzyme, Rubisco, within a virus-like polyhedral protein shell. Carboxysomes provide significantly elevated levels of CO2 around Rubisco to maximize carboxylation and reduce wasteful photorespiration, thus functioning as the central CO2-fixation organelles of bacterial CO2-concentration mechanisms. Their intriguing architectural features allow carboxysomes to make a vast contribution to carbon assimilation on a global scale. In this review, we discuss recent research progress that provides new insights into the mechanisms of how carboxysomes are assembled and functionally maintained in bacteria and recent advances in synthetic biology to repurpose the metabolic module in diverse applications. organisms that can grow using energy from solar light and perform photosynthesis without evolving oxygen. proteinaceous megadalton-complexes that encapsulate metabolic pathways within the subcellular 'microfactories' using a virus-like protein shell to enhance enzymatic functions. a chemical process that is catalysed by Rubisco to fix CO2 to the five-carbon compound ribulose-1,5-bisphosphate (RuBP) and the splitting of the resulting six-carbon compound into two molecules of the three-carbon compound 3-phosphoglycerate (3-PGA). a type of bacterial microcompartment that sequesters Rubisco and carbonic anhydrase (CA) to increase the rate of carbon fixation. organisms that derive energy from the oxidation of inorganic compounds. the bacterial microcompartments that encase pathway enzymes for the catabolism of various metabolites, including choline, ethanolamine, and 1,2-propanediol. the specialized structures that compartmentalize specific enzymes, pathways, and functions within a cell to improve and regulate metabolic performance. a chemical process in which Rubisco adds O2 to RuBP to produce 3-PGA and 2-phosphoglycolate (2-PG). The latter is subsequently recycled along the following metabolic pathway known as photorespiration. a process including the oxygenation of RuBP by Rubisco and release of CO2 from organic compounds. It is assumed to be a wasteful process as it causes a net loss of CO2 and consumes energy (ATP and NADPH) produced in photosynthesis. However, photorespiration plays a protective role in regulating photosynthesis and is especially vital under stress conditions.