The portal protein of P22 and similar Podoviridae tail phages is a dodecameric structure consisting of a hip (2), a leg(1) and a barrel(3). DNA viruses such as bacteriophages and herpesviruses deliver their genome into and out of the capsid through large proteinaceous assemblies, known as portal proteins. Domains 1 and 3 are mostly helical and form the majority of the DNA-translocating channel. Domain 2 adopts an alpha-beta-fold characterised by two sheets of eight beta-strands, which cross each other to form a beta-barrel-like structure [1].

1: Three-dimensional structure of a viral genome-delivery portal vertex. Olia AS, Prevelige PE Jr, Johnson JE, Cingolani G; Nat Struct Mol Biol. 2011;18:597-603. PMID:21499245