THE BINDING OF PSEUDOMONAS-AERUGINOSA PILI TO GLYCOSPHINGOLIPIDS IS A TIP-ASSOCIATED EVENT INVOLVING THE C-TERMINAL REGION OF THE STRUCTURAL PILIN SUBUNIT

pill are one of the adhesins of Pseudomonas aeruginosa that mediate adherence to epithelial cell-surface receptors. The pill of P. aeruginosa strains PAK and PAO were examined and found to bind gangliotetraosyl ceramide (asialo-GM(1)) and, to a lesser extend, (IIN)-N-3- acetylneuraminosylgangliotetraosyl ceramide (GM(1)) in solid-phase binding assays. Asialo-GM(1), but not GM(1), inhibited both PAK and PAO pill binding to immobilized asialo-GM(1) on the microtitre plate. PAO pill competitively inhibited PAK pill binding to asialo-GM(1), suggesting the presence of a structurally similar receptor-binding domain in both pilus types. The interaction between asialo-GM(1) and pill occurs at the pilus tip as asialo-GM(1) coated colloidal gold only decorates the tip of purified pill. 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 pill 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 ah, 1992), binds only to the tip of PAK pill; (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-GM(1) and inhibit the binding of pill to the glycolipid; (iii) PK99H was shown to block PAK pilus binding to asialo-GM(1). Monoclonal antibody PK3B had no effect on PAK pill binding to asialo-GM(1). 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.