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. Homopentamer. The base of the pyramid faces outward. Not essential for BMC formation; when an artificial operon without BMC-P proteins (Hoch_5815, Hoch_5812, Hoch_3341, Hoch_5816) is expressed in E.coli 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). 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). One of 3 BMC-P proteins in this bacteria, the others are Hoch_4425 and Hoch_4426. Belongs to the CcmL/EutN family.