Pseudomonas aeruginosa cytotoxin: the Asp197-Gly-Asp-Tyr-His-Tyr-His-Tyr202 containing loop is critical for plasma membrane binding

The cytotoxin from Pseudomonas aeruginosa is a pore-forming toxin that binds specifically to water channel-related molecules of the erythrocyte membrane. Here, we have defined a domain, Asp197-Gly-Asp-Tyr-His-Tyr202 of the cytotoxin, to be essential for receptor binding. Cytotoxin point mutants from the recombinant gene carrying substitutions in the domain were characterized in terms of inhibiting the binding of radioiodinated natural cytotoxin to rat erythrocyte and producing cytotoxic effects in human granulocytes. A synthetic peptide representing residues 191–211 of the cytotoxin acted as a competitive inhibitor at a concentration of 10−5 M. In contrast, two other cytotoxin-specific peptides were inactive. Structure prediction of the binding sequence shows a loop structure with similarities to the sequence around His332 in Aeromonas aerolysin essential to receptor binding.