Pseudomonas aeruginosa is a Gram-negative opportunistic bacterial pathogen that can cause chronic
infection of the lungs of cystic fibrosis patients. Chaperone-usher systems in P. aeruginosa are known
to translocate and assemble adhesive pili on the bacterial surface and contribute to biofilm formation
within the host. Here, we report the crystal structure of the tip adhesion subunit CupB6 from the
cupB1-6 gene cluster. The tip domain is connected to the pilus via the N-terminal donor strand from
the main pilus subunit CupB1. Although the CupB6 adhesion domain bears structural features similar
to other CU adhesins it displays an unusual polyproline helix adjacent to a prominent surface pocket,
which are likely the site for receptor recognition.