The binding of Pseudomonas aeruginosa pili to glycosphingolipids is a tip-associated event involving the C-terminal region of the structural pilin subunit

Pili are one of the adhesins of Pseudomonas aeruginosa that mediate adherence to epithelial cell-surface receptors. The pili of P. aeruginosa strains PAK and PAO were examined and found to bind gangliotetraosyl ceramide (asialo-GM₁) and, to a lesser extend, ll³N-acetylneuraminosylgangliotetraosyl ceramide (GM₁) in solid-phase binding assays. Asialo-GM₁, but not GM₁, inhibited both PAK and PAK pili binding to immobilized asialo-GM₁ on the microtitre plate. PAO pili competitively inhibited PAK pili binding to asialo-GM₁, suggesting the presence of a structurally similar receptor-binding domain in both pilus types. The interaction between asialo-GM₁ and pili occurs at the pilus tip as asialo-GM₁ coated colloidal gold only decorates the tip of purified pili. Three sets of evidence suggest that the C-terminal disulphide-bonded region of the Pseudomonas pilin is exposed at the tip of the pilus: (i) immunocytochemical studies indicate that P. aeruginosa pili have a basal-tip structural differentiation where the monoclonal antibody (mAb) PK3B recognizes an antigenic epitope displayed only on the basal ends of pili (produced by shearing) while the mAb PK99H, whose antigenic epitope resides in residues 134–140 (Wong et al., 1992), binds only to the tip of PAK pili; (ii) synthetic peptides, PAK(128–144)^ox-OH and PAO(128–144)^ox-OH, which correspond to the C-terminal disulphide-bonded region of Pseudomonas pilin are able to bind to asialo-GM₁ and inhibit the binding of pili to the glycolipid; (iii) PK99H was shown to block PAK pilus binding to asialo-GM₁ Monoclonal antibody PK3B had no effect on PAK pili binding to asialo-GM₁ Thus, the adherence of the Pseudomonas pilus to glycosphingolipid receptors is a tip-associated phenomenon Involving a tip-exposed C-terminal region of the pilin structural subunit.