Carboxysome

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Carboxysomes are polyhedral protein shells of the bacterial microcompartment group of supramolecular complexes involved in carbon fixation^{[citation needed]}. Carboxysomes encapsulate enzymes involved in carbon fixation and are thought to concentrate carbon in the form of carbon dioxide to overcome the inefficiency of RuBisCo, the predominant enzyme in carbon fixation and the rate limiting enzyme in the Calvin cycle. Carboxysomes are thought to be part of a wider group of protein micro-compartments that have dissimilar functions, but similar structures, based on homology of the two shell protein families^[1]

[edit] Architecture

Structurally, carboxysomes have been shown to be icosahedral, or quasi-icosahedral, typically around 120 nm in diameter. Proteins known to form the shell have been structurally characterized by X-ray crystallography, revealing that one family forms cyclical hexamers^{[citation needed]} while another forms pentamers^{[citation needed]}. In direct analogy to many known viral structures^{[citation needed]} this suggested that the carboxysome is icosahedral. Electron cryo-tomography studies^{[citation needed]} have subsequently confirmed this, leading to a model based on a synthesis of molecular structures and gross morphology^[2]

[edit] Occurrence

Carboxysomes are found in all cyanobacteria, some nitrifying bacteria, and thiobacilli.

[edit] References

1. ^ Cannon GC, Bradburne CE, Aldrich HC, Baker SH, Heinhorst S, Shively JM (2001). "Microcompartments in prokaryotes: carboxysomes and related polyhedra". Appl. Environ. Microbiol. 67 (12): 5351–61. doi:10.1128/AEM.67.12.5351-5361.2001. PMID 11722879. 
2. ^ Tanaka S, Kerfeld CA, Sawaya MR, et al (2008). "Atomic-level models of the bacterial carboxysome shell". Science (journal) 319 (5866): 1083–6. doi:10.1126/science.1151458. PMID 18292340.