Mapping of linear B-cell epitopes of the S2 subunit of pertussis toxin

The linear immunogenic and antigenic structure of the S2 subunit of pertussis toxin was investigated with synthetic peptides corresponding to regions of the protein sequence predicted to contain surface-exposed hydrophilic beta turns. Five peptides as peptide-bovine serum albumin conjugates were recognized by anti-pertussis toxin antiserum and were thus designated "immunogenic epitopes." Two prominent immunogenic epitopes were specified by peptides corresponding to sequences spanning R107-120 and R186-199, whereas peptides corresponding to residues R35-50 and R91-106 were only bound in low titer. Three peptides as thyroglobulin conjugates elicited antisera in rabbits that bound intact pertussis toxin by enzyme-linked immunosorbent assay and immunoblot. These peptides were designated "antigenic epitopes." The most prominent antigenic determinant was localized to the N-terminal end of the S2 sequence encompassing residue R1-7. Peptides R35-50 and R91-106 represented two minor antigenic epitopes. Antisera to two additional peptides corresponding to residues R134-149 and R186-199 recognized the S2 subunit only by Western blotting (immunoblotting). Only antiserum raised against peptide R91-106 also recognized the S3 subunit by Western blotting, indicating a marked antigenic and probably also structural difference between the two highly homologous subunits.