Forms vertices in bacterial microcompartment (BMC) shells. 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 BMC with a molecular mass of 6.5 MDa. There are 12 BMC-P pentamers per BMC. The shell facets are 20-30 Angstroms thick, with 1 of BMC-T trimers protruding to the exterior