Forms the portal vertex of the capsid (PubMed:21499245). This portal plays critical roles in head assembly, genome packaging, neck/tail attachment, and genome ejection (PubMed:30787152). Procapsid assembly may initiate with a nucleation complex composed of portal and scaffolding proteins (PubMed:30787152). The portal protein multimerizes as a single ring-shaped homododecamer arranged around a central channel (PubMed:21499245, PubMed:28134243). Switches upon genome packaging from an asymmetrical conformation in the procapsid (PC-portal) to a symmetrical ring in the mature capsid (MV-portal). This change of conformation may serve as a signal for headful packaging (PubMed:28134243). Homododecamer (PubMed:21499245). Interacts with the terminase large subunit; this interaction allows the packaging of viral DNA (PubMed:28134243). Interacts with gp4; this interaction participates in the head completion (PubMed:28134243). Belongs to the p22likevirus portal protein family.