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.

This family belongs to the Phage Portal Protein (PPP) Superfamily.



Lokareddy, R.K., R.S. Sankhala, A. Roy, P.V. Afonine, T. Motwani, C.M. Teschke, K.N. Parent, and G. Cingolani. (2017). Portal protein functions akin to a DNA-sensor that couples genome-packaging to icosahedral capsid maturation. Nat Commun 8: 14310.


TC#NameOrganismal TypeExample

Samonella phage P22 portal protein 1 of 725 aas and no TMSs. It forms a dodecameric ring structure and plays an important role in ejection of the phage DNA, through the cell envelope, into the host cell cytoplasm (Lokareddy et al. 2017). See family description for more details.

Portal protein of Salmonella phage P22


Phage portal protein of 703 aas.

PP of EBPR podovirus 1


Phage portal protein of 623 aas

Portal protein of Bartonella alsatica


Portal protein of 749 aas

PP of Comamonas testosteroni


Coil containing protein of 696 aa

Coil-containing protein of Vibrio phage 1.205.O.


Putative phage portal protein of 701 aa

PPP of a prokaryotic dsDNA virus


Uncharacterized protein of 697 aas

UP of Tatlockia micdadei


Portal protein p19 of 750 aas.  This protein reveals good extensive similarity with other members of the subfamily with TC#s 1.W.1.1, but also with the hydrophilic domain of TC# 1.W.1.2.1 (e-11).  The N-terminal hydrophobic domain is lacking in this protein.

PP of Acinetobacter harbinensis


Uncharacterized protein of 613 aas.

UP of Fibrobacter sp. UWP2


TC#NameOrganismal TypeExample