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

Abstract

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 b-helical tip (gp37) from the Salmonella phage S16 LTF. Gp38 contains rare polyglycine type II helices folded into a packed lattice, herein designated ''PG II 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.

Small angle X‐ray scattering‐assisted protein structure prediction in CASP13 and emergence of solution structure differences

“…Crystallographers generously provided a total of 10 protein samples. Marianne Ilbert provided protein for S0949; Petr Leiman, S0953/6F45.PDB; Karoline Michalska, S0957/6CP8.PDB and S0968/6CP9.PDB; Owen Davies, S0980/6GNX.PDB, Chi‐lin Tsai, S0975; Mark van Raaij, S0981; Jose Henrique Pereira, S0985; Lindsey Spiegelman, S0987, and Andrew Lovering, S0992. An eleventh SAXS data set (S0999) was made available by Marcus Hartmann.…”

Target highlights in CASP13: Experimental target structures through the eyes of their authors

“…Unsurprisingly, the structure and function of gp38 and its homologs (commonly named “adhesins”) have been of great interest ever since they were discovered as the determinants of phage host range . Thus, by solving the crystal structure of a distal part of gp37 connected to gp38 from phage S16 we aimed to advance our understanding of this important family of adhesins (Figure B) …”

“…S16 is a relative of the well‐studied phage T4. Both phages are equipped with baseplate‐attached long tail fibers (LTFs) that mediate receptor‐binding through their distal tips . We recently exploited the Salmonella‐ specific binding of the S16 LTF as a tool for rapid, ELISA‐like detection of Salmonella contaminants in food …”

“…Both phages are equipped with baseplate-attached long tail fibers (LTFs) that mediate receptor-binding through their distal tips. [64][65][66][67][68] We recently exploited the Salmonella-specific binding of the S16 LTF as a tool for rapid, ELISA-like detection of Salmonella contaminants in food. 69 The T4 and S16 LTFs are similar to each except for the structure of their distal tip that interacts with the host cell surface during host recognition.…”

CASP13 target classification into tertiary structure prediction categories

“…In addition to missing the first helix found in HEH domains, the extended region and third helix are shorter in the target domain, bringing into question any potential evolutionary relationship.Five potential new folds were represented in three CASP13 targets. First, the Salmonella phage S16 gp38 adhesin includes a low complexity polyglycine rich sequence (T0953s2-D3) that folds into a compact fiber of packed type II helices35 (Figure 2B, red domain). While type II helices are present in the structure database, their arrangement into this topology is new.…”