This family features sequences bearing similarity to the C-terminal portion of the bacteriophage T4 protein fibritin (Swiss:P10104). This protein is responsible for attachment of long tail fibres to virus particle, and forms the 'whiskers' or fibres on the neck of the virion. The region seen in this family contains an N-terminal coiled-coil portion and the C-terminal globular foldon domain (residues 457-486), which is essential for fibritin trimerisation and folding [1]. This domain consists of a beta-hairpin; three such hairpins come together in a beta-propeller-like arrangement in the trimer, which is stabilised by hydrogen bonds, salt bridges and hydrophobic interactions [1].

1: Very fast folding and association of a trimerization domain from bacteriophage T4 fibritin. Guthe S, Kapinos L, Moglich A, Meier S, Grzesiek S, Kiefhaber T; J Mol Biol 2004;337:905-915. PMID:15033360