The only hexameric shell protein in this bacterium, it forms the majority of the bacterial microcompartment (BMC) shell. Expression of 5 proteins in E.coli (BMC-H (Hoch_5815), BMC-P (Hoch_5814), and 3 BMC-T (Hoch_5812, Hoch_5816, Hoch_3341)) forms a 40 nm artificial BMC with a molecular mass of 6.5 MDa. There are 60 BMC-H hexamers per BMC. The shell facets are 20-30 Angstroms thick (a single hexamer layer), with 1 of BMC-T trimers protruding to the exterior. Homohexamer with a small central pore (PubMed:26617073, PubMed:28642439, PubMed:31075444, PubMed:30833088) (Probable). When purified protein is examined by atomic force microscopy it dynamically makes uniform patches about 35 Angstroms thick with hexamers in the same orientation (PubMed:26617073). In the BMC the concave side faces outward, with the N- and C-terminii exposed to the cytoplasm (PubMed:28642439). Absolutely required for BMC formation; when deleted from an artificial operon (Hoch_5815, Hoch_5812, Hoch_3341, Hoch_5816, Hoch_4425, Hoch_4426, Hoch_5814) being expressed in E.coli, no BMC shells are made. Artificial BMCs can be made in E.coli by expressing (Hoch_5815, Hoch_5812, Hoch_3341, Hoch_5816, Hoch_4425, Hoch_4426, Hoch_5814) or (BMC-H (Hoch_5815), BMC-P (Hoch_5814), and 3 BMC-T (Hoch_5812, Hoch_5816, Hoch_3341)). Cargo proteins can be targeted to this BMC (PubMed:24631000, PubMed:28642439). Artificial BMCs can be made by duplicating this gene with a 16 residue linker between the copies (making an artificial BMC-T). The shell assembles into balls with holes where the pentameric subunit would be, and can be used as a model to study assembly and permeability (PubMed:30901520). Additional changes to this protein place the N- and C-terminii in the interior of the shell (called CPH). Fusing proteins to the C-terminus of CPH allows targeting of cargo proteins to the lumen of the organelle composed of CPH, BMC-P and BMC-T1 (PubMed:31075444). Belongs to the bacterial microcompartments protein family.