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. One of 2 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 the stacked BMC-T trimers protruding to the exterior (PubMed:28642439, PubMed:30833088). The stacked trimers may serve as conduits to allow metabolite flux across the protein shell, gated by Arg-68 which contacts Glu-67 in an adjacent subunit; they are flexible enough to play a role in accommodating variations in shell assembly (Probable). Homotrimerizes to form a pseudohexamer. These stack, with the concave faces together, with the concave faces together, in purified bacterial microcompartments (BMC). 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; in the stacked homohexamer both pores are closed (PubMed:28642439). In the BMC the inner pore is fully or partially closed while the outer pore is closed (PubMed:30833088). Not 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 2-fold decrease in BMC formation 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. Belongs to the EutL/PduB family.