Gp38 adhesins of Straboviridae phages recognize specific extracellular loops of outer membrane protein receptors.

Tailed bacteriophages (phages) depend on specific interactions with their host receptors for efficient infection and propagation. Gp38 is a unique receptor-binding protein located at the distal tail of Straboviridae phages characterized by a defined modular, monomeric structure. Here, we demonstrated that the similarity of Gp38 adhesins, encoded by related yet distinct Straboviridae phages belonging to Tequatrovirus, Mosigvirus, and Krischvirus, determines the recognition of receptors such as Tsx, OmpF, and OmpA. For OmpA, experimental and in silico analysis identified specific outer loops protruding from the receptor required for phage infection by interacting with Gp38. Yet, the loops involved are dependent on the adhesin variant. In-depth in silico analysis identified two groups of Gp38 adhesins differentially interacting with OmpA by expressing specific amino acids. This demonstrates that both partners' diversity affects phage binding and host range. Overall, the phylogeny of Gp38 adhesins can predict receptor binding essential for advancing phage therapy.