Recent insights into α-carboxysome structure, mechanism, and assembly

Bacterial microcompartments (BMCs) are pseudo-organelles that sequester metabolic enzymes, intermediates, and/or gases within the bacterial cytosol. One model BMC is the carboxysome (CB). CBs facilitate rubisco-driven fixation of CO₂, increasing efficiency and maximizing the phosphoglycerate output in CB-containing bacteria. The α-CBs are of particular interest due to their small size and relative simplicity, making them ideal targets for bioengineering applications. These CBs were the first BMC observed and have been a long-studied model; however, they are challenging to study in native systems and in purified samples. Recent advances in cryogenic electron microscopy and cryogenic electron tomography have resulted in many new published structures of the shell proteins, shell assemblies, and cargo organization within the CB. These new insights have advanced the field's understanding of important structural interfaces, shed insights into once unknown domain functions, and the complex mechanisms involved in assembly and maintenance of the CB. This review highlights recently published structures of α-CB proteins and the functional and mechanistic findings of these studies.