Comparative study of immunological and structural properties of two recombinant vaccine candidates against botulinum nurotoxin type E

ABSTRACT

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: