SMART accession number:SM00877
Description: Bacterial microcompartments are primitive organelles composed entirely of protein subunits. The prototypical bacterial microcompartment is the carboxysome, a protein shell for sequestering carbon fixation reactions. These proteins for hexameric structure.
Interpro abstract (IPR000249):

This domain is found in a variety of polyhedral organelle shell proteins (CcmK), including CsoS1A, CsoS1B and CsoS1C of Thiobacillus neapolitanus (Halothiobacillus neapolitanus) and their orthologs from other bacteria.

Some autotrophic and non-autotrophic organisms form polyhedral organelles, carboxysomes/enterosomes [ (PUBMED:11722879) ]. The best studied is the carboxysome of Halothiobacillus neapolitanus, which is composed of at least 9 proteins: six shell proteins, CsoS1A, CsoS1B, CsoS1C, Cso2A, Cso2B and CsoS3 (carbonic anhydrase) [ (PUBMED:14729686) ], one protein of unknown function and the large and small subunits of RuBisCo (CbbL and Cbbs). Carboxysomes appear to be approximately 120 nm in diameter, most often observed as regular hexagons, with a solid interior bounded by a unilamellar protein shell. The interior is filled with type I RuBisCo, which is composed of 8 large subunits and 8 small subunits; it accounts for 60% of the carboxysomal protein, which amounts to approximately 300 molecules of enzyme per carboxysome. Carboxysomes are required for autotrophic growth at low CO 2 concentrations and are thought to function as part of a CO 2 -concentrating mechanism [ (PUBMED:15012219) (PUBMED:9891798) ].

Polyhedral organelles, enterosomes, from non-autotrophic organisms are involved in coenzyme B 12 -dependent 1,2-propanediol utilisation (e.g., in Salmonella enterica [ (PUBMED:10498708) ]) and ethanolamine utilisation (e.g., in Salmonella typhimurium [ (PUBMED:7868611) ]). Genes needed for enterosome formation are located in the 1,2-propanediol utilisation pdu [ (PUBMED:11844753) (PUBMED:10498708) ] or ethanolamine utilisation eut [ (PUBMED:7868611) (PUBMED:10464203) ] operons, respectively. Although enterosomes of non-autotrophic organisms are apparently related to carboxysomes structurally, a functional relationship is uncertain. A role in CO 2 concentration, similar to that of the carboxysome, is unlikely since there is no known association between CO 2 and coenzyme B12-dependent 1,2-propanediol or ethanolamine utilisation [ (PUBMED:11844753) ]. It seems probable that entrosomes help protect the cells from reactive aldehyde species in the degradation pathways of 1,2-propanediol and ethanolamine [ (PUBMED:11722879) ].

Family alignment:
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There are 13168 BMC domains in 10616 proteins in SMART's nrdb database.

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