Many tailed bacteriophages (Caudovirales) use fibre proteins for initial, reversible, host cell lipo-polysaccharide recognition. Some phages also use them for secondary, irreversible, host cell attachment. Modification by natural or experimental mutation of bacteriophage receptor-binding domains may allow retargeting of phages to alternative host bacteria.
For the myovirus T4, we have solved the structures of the carboxy-terminal domains of the short fibre protein gp12, the proximal long tail fibre protein gp34 and the distal long tail fibre protein gp37. All three proteins display beta-structured folds, with gp12 containing a central metal ion, gp34 having a long triple beta-helix and gp37 a thin needle domain in which seven iron ions are located.
For the siphovirus T5, the L-shaped tail fibre is formed by trimers of the pb1 protein. The L-shaped tail fibres have an intra-molecular chaperone domain, which is auto-proteolytically removed after correct trimerization and folding. We solved the structure of the carboxy-terminal domain of pb1 in presence and absence of the chaperone domain. The carboxy-terminal domain of pb1 revealed an intertwined beta-structured fold, while the chaperone domain is mainly alpha-structured, with long beta-hairpins embracing the fibre domain it helps to assemble.
For the podovirus T7, we have solved the structure of the carboxy-terminal domain of the fibre, which is formed by a trimer of the gp17 protein. Site-directed mutagenesis of exposed residues at the end of the fibre identified those important for infection of E. coli, and some residues were identified that, when mutated, limited the host range to B-type E. coli or K-type E. coli.
For the podovirus epsilon15, the high-resolution structure of the carboxy-terminal domain of the fibre revealed a monomeric domain, with mixed alpha-beta structure. The domain may have enzymatic activity.