Salmonella Phage S16 Tail Fiber Adhesin Features a Rare Polyglycine Rich Domain for Host Recognition

The ability of phages to infect specific bacteria has led to their exploitation as bio-tools for bacterial remediation and detection. Many phages recognize bacterial hosts via adhesin tips of their long tail fibers (LTFs). Adhesin sequence plasticity modulates receptor specificity, and thus primarily defines a phage's host range. Here we present the crystal structure of an adhesin (gp38) attached to a trimeric β-helical tip (gp37) from the Salmonella phage S16 LTF. Gp38 contains rare polyglycine type II helices folded into a packed lattice, herein designated “PGII sandwich.” Sequence variability within the domain is limited to surface-exposed helices and distal loops that form putative receptor-binding sites. In silico analyses revealed a prevalence of the adhesin architecture among T-even phages, excluding the archetypal T4 phage. Overall, S16 LTF provides a valuable model for understanding binding mechanisms of phage adhesins, and for engineering of phage adhesins with expandable or modulated host ranges. [Display omitted] •Crystal structure of Salmonella phage S16 long tail fiber adhesin tip (gp38-gp37)•Gp38 features rare polyglycine type II (PGII) helices folded into a PGII sandwich•Exposed residues of the PGII sandwich are determinants of host binding•S16 adhesin architecture is prevalent among the important T-even phage family Dunne et al. present the crystal structure of the adhesin tip (gp38) of the Salmonella bacteriophage S16 long tail fiber. Gp38 contains rare polyglycine type II (PGII) helices arranged as a three-layered “PGII sandwich.” Surface residues on the PGII sandwich are key determinants of phage-host interaction.