Inhibition of pertussis toxin binding to model receptors by antipeptide antibodies directed at an antigenic domain of the S2 subunit

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Receptor recognition of pertussis toxin is mediated by the B-oligomer consisting of subunits S2, S3, S4 (two), and S5. To understand the structure-function relationships of the receptor-binding oligomer and to elucidate the immunological structure of pertussis toxin, we assayed antisera generated against each of 10 synthetic peptides corresponding to segments of the pertussis toxin S2 subunit for their ability to recognize the native toxin. Only antisera raised against peptides R1-7, R35-50, and R91-106 recognized pertussis toxin in an enzyme-linked immunosorbent assay and Western blotting (immunoblotting). These segments thus correspond to linear antigenic epitopes. The highly homologous S3 subunit was only weakly recognized by antibodies to R91-106 in Western blotting. The ability of affinity-purified antipeptide antibodies to interfere with the binding of pertussis toxin was investigated by pertussis toxin-mediated hemagglutination of goose erythrocytes, the binding of pertussis toxin to fetuin, and the toxin-induced clustered growth pattern of CHO cells as model receptor systems. Antibodies directed against synthetic peptides R1-7, R35-50, and R91-106 inhibited the binding of pertussis toxin in the two model receptor systems that solely depend on the interactions of the S2 subunit. The toxin-mediated clustered growth pattern of CHO cells could not be inhibited. The results point to a second binding site with distinct specificity involving the S3 subunit of pertussis toxin. The regions identified in this work contribute to the definition of receptor-binding sites of pertussis toxin and should thus improve the development of an acellular-component pertussis vaccine.