Comparative Study of Immunological and Structural Properties of Two Recombinant Vaccine Candidates against Botulinum Neurotoxin Type E

Recently، botulinum neurotoxin (BoNT) -derived recombinant proteins have been suggested as potential botulism vaccines. Here، with concentrating on BoNT type E (BoNT/E)، we studied two of these binding domain-based recombinant proteins: a multivalent chimer protein، which is composed of BoNT serotypes A، B and E binding subdomains، and a monovalent recombinant protein، which contains 93 amino acid residues from recombinant C-terminal heavy chain of BoNT/E (rBoNT/E-HCC). Both proteins have an identical region (48 aa) that contains one of the most important BoNT/E epitopes (YLTHMRD sequence). The recombinant protein efficiency in antibody production، their structural differences، and their BoNT/E-epitope location were compared by using ELISA، circular dichroism، computational modeling، and hydrophobicity predictions. Immunological studies indicated that the antibody yield against rBoNT/E-HCC was higher than chimer protein. Cross ELISA confirmed that the antibodies against the chimer protein recognized rBoNT/E-HCC more efficiently. However، both antibody groups (anti-chimer and anti-rBoNT/E-HCC antibodies) were able to recognize other proteins. Structural studies with circular dichroism showed that chimer proteins have slightly more secondary structures than rBoNT/E-HCC. The immunological results suggested that the above-mentioned identical region in rBoNT/E-HCC is more exposed. Circular dichroism، computational protein modeling and hydrophobicity predictions indicated a more exposed location for the identical region in rBoNT/E-HCC than the chimer protein، which is strongly in agreement with immunological results.