The Phage Portal Protein 1 (PPP1) Family
This family consists of proteins that form the portal vertex of the capsid of Salmonella phage P22 and other phage (Olia et al. 2011). This portal plays critical roles in head assembly, genome packaging, neck/tail attachment, and genome ejection (Motwani and Teschke 2019). Procapsid assembly may initiate with a nucleation complex composed of portal and scaffolding proteins (Motwani and Teschke 2019).
The portal protein multimerizes as a single ring-shaped homododecamer
arranged around a central channel. 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 (Lokareddy et al. 2017). It plays a role in viral genome ejection from the phage, through the host cell envelope, into the cell cytoplasm. These proteins are encoded in phage and bacterial genomes.