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

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.