1.W.8.  The (Enterobacterial phage T4) Portal Protein 8 (PPP8) Family 

The phage T4 protein forms the portal vertex of the capsid (Michaud et al. 1989; Padilla-Sanchez et al. 2014). This portal plays critical roles in head assembly, genome packaging, neck/tail attachment, and genome ejection into the cytoplasm of the host cell. The portal protein multimerizes as a single ring-shaped homododecamer arranged around a central channel and binds to the terminase subunits to form the packaging machine. It attaches to the host inner membrane, most likely through interaction with the host YidC protein and forms together with chaperone gp40 an initiator complex to form the prohead Fokine et al. 2004; Quinten and Kuhn 2012).

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



Fokine, A., P.R. Chipman, P.G. Leiman, V.V. Mesyanzhinov, V.B. Rao, and M.G. Rossmann. (2004). Molecular architecture of the prolate head of bacteriophage T4. Proc. Natl. Acad. Sci. USA 101: 6003-6008.

Michaud, G., A. Zachary, V.B. Rao, and L.W. Black. (1989). Membrane-associated assembly of a phage T4 DNA entrance vertex structure studied with expression vectors. J. Mol. Biol. 209: 667-681.

Padilla-Sanchez, V., S. Gao, H.R. Kim, D. Kihara, L. Sun, M.G. Rossmann, and V.B. Rao. (2014). Structure-function analysis of the DNA translocating portal of the bacteriophage T4 packaging machine. J. Mol. Biol. 426: 1019-1038.

Quinten, T.A. and A. Kuhn. (2012). Membrane interaction of the portal protein gp20 of bacteriophage T4. J. Virol. 86: 11107-11114.


TC#NameOrganismal TypeExample

The (Enterobacterial phage T4) Portal Protein, gp20, of 524 aa

gp20 of Enterobacterial phage T4


Uncharacterized protein of 647 aas

UP of Hyphomicrobiaceae bacterium


Phage portal vertex protein of 731 aa

PPP of Bacillus phage AR9


Vertex protein of head of 534 aa

Vertex protein of Bacillus phage vB_BceM-HSE3


Uncharacterized protein of 582 aas

UP of Bacteroidetes bacterium HGW-Bacteroidetes-1 (groundwater metagenome)


Similar to portal vertex protein of head of 533 aa

UP of Rhodothermus phage RM378


Uncharacterized bacteriophage T4-like capsid assembly protein (Gp20 of 1011 aas

UP of uncultured archaeon


Portal vertex protein of 577 aa

PPP of Tenacibaculum phage PTm1


Uncharacterized protein of 471 aas

UP of Thermococci archaeon