Bacterial microcompartments (BMCs) serve to isolate certain enzymatic pathways from the rest of the cell. BMCs performing five different functions have been characterized, including the archetypical carbon fixation by RuBisCO in the carboxysome, yet bioinformatics analysis suggests additional functions await discovery. Two new studies now investigate these computational clues. Wheatley et al. focused on an unusual gene within some carboxysome operons homologous to pterin-utilizing enzymes. Bioinformatics, structural and functional analysis confirmed that the protein, newly named acRAF, was not enzymatically active. Instead, the authors suspected it might be functionally equivalent to RbcX, a protein found in carboxysome operons that do not contain acRAF, which chaperones RuBisCO assembly by stabilizing dimers en route to functional hexadecamers. Indeed, RuBisCO assembly in the presence of the newly named acRAF and the chaperone GroELS greatly increased compared to assembly in the presence of GroELS alone. Erbilgin et al., in contrast, investigate the function of an uncharacterized microcompartment conserved in Planctomycetes and Verrucomicrobia, bacteria known to be associated with algae rich in sulfated polysaccharides. Directed gene knockouts demonstrated this 'PV BMC' (shown in blue in the false-colored image) was important for the metabolism of several carbon sources, particularly L-fucose, L-rhamnose and the physiologically relevant polysaccharide fucoidan. The authors also confirmed the presence of BMC-like structures in cells grown on fucose or rhamnose but not glucose. These studies expand our understanding of these intriguing organelles.
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Goodman, C. Contain yourself. Nat Chem Biol 10, 240 (2014). https://doi.org/10.1038/nchembio.1488
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DOI: https://doi.org/10.1038/nchembio.1488
