Hundreds of species of bacteria produce large subcellular organelles known as microcompartments (MCPs), which consist of metabolic enzymes encapsulated within proteinaceous shells reminiscent of viral capsids. For MCPs to function, substrates and products must move across their outer protein shell, which lacks any lipid-based membrane. 3D structures of the proteins that comprise MCP shells have revealed narrow pores through their centers that are the routes by which substrates enter (and products escape from) MCPs. The shells of MCPs are assembled primarily from a family of small proteins that have bacterial microcompartment (BMC) domains PMID:25713376.

This entry represents the BMC domain which 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 (INTERPRO:IPR000249) .