Structural diversification of phage tail fibres enables recognition of diverse type IV pili

ABSTRACT Viruses must recognize receptors on host surfaces to initiate infection, but these receptors can evolve rapidly, posing a fundamental challenge to viral persistence. The type IV pilus of Pseudomonas aeruginosa is an ideal model system to study virus-receptor coevolution because its major pilin subunit PilA exhibits extensive sequence and chemical diversity while remaining essential for phage attachment. Here, we combined large-scale comparative genomics with structural and functional analyses to determine how pilus-dependent phages maintain infectivity despite extensive receptor diversification. Pilin variation was concentrated at solvent-exposed regions, altering filament surface chemistry while preserving key subunit-subunit interfaces. Despite this variation, phages recognized divergent pilins more effectively than polyclonal antisera. However, phages differed markedly in their sensitivity to receptor perturbation: some required electrostatic and structural compatibility, whereas others tolerated substantial receptor modification, including the presence of post-translational glycosylation. Comparisons of AlphaFold3 structural models revealed two distinct tail fibre architectures associated with those phenotypes. Phages encoding tail fibres with conserved receptor-binding domains were more sensitive to receptor perturbation within a given pilin background, while those with structurally diversified binding regions infected strains expressing highly divergent pilins. Together, these findings suggest that modular diversification of receptor-binding proteins provides a structural route by which phages accommodate receptor evolution. SIGNIFICANCE Understanding the determinants of viral host range is essential for explaining how viruses persist in the face of receptor diversification. Using pilus-dependent bacteriophages that bind diverse type IV pilins in Pseudomonas aeruginosa , we show that differences in tail fibre architecture are associated with distinct sensitivities to receptor variation. Phages with structurally conserved receptor-binding regions are sensitive to receptor perturbation, whereas those with diversified binding architectures remain infectious across strains expressing highly divergent pilins. Our results identify a structural correlate of receptor recognition breadth and reveal how receptor-binding protein architecture contributes to viral host range and adaptation. These data can inform the selection or engineering of broad-host range phages for therapeutic applications.