A minor component 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 40 nm artificial BMCs with a molecular mass of 6.5 MDa. This protein does not form stacked pseudohexamers in the BMC. There are 20 BMC-T pseudohexamers per BMC, composed of mixed BMC-T1, BMC-T2 and BMC-T3. The shell facets are 20-30 Angstroms thick, with 1 of BMC-T trimers protruding to the exterior. Homotrimerizes to form a pseudohexamer (PubMed:28642439, PubMed:30833088, PubMed:26704697). Unlike its paralogs BMC-T2 and BMC-T3, the pseudohexamers do not stack. The concave side faces outward, with the N- and C-terminii exposed to the cytoplasm (PubMed:28642439, PubMed:30833088). These proteins have 2 BMC domains which evolve independently of each other, giving the term pseudohexamer to the trimerized subunit. Although the homotrimer fills the approximate space of a BMC hexamer protein, the BMC-T trimers are more compact. Their universal presence in BMCs indicates their structural importance. The homohexamers form pores of at least 5 Angstroms in diameter. Required for efficient 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, a >10-fold decrease in BMC shells is seen. 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). BMC-H can be modified to place its 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). This subunit has been modifed to bind a 4Fe-4S center, which is the first step in conferring electron-transfer function to BMCs (PubMed:26704697). Belongs to the bacterial microcompartments protein family.