Contribution of defined amino acid residues to the immunogenicity of recombinant Escherichia coliheat‐stable enterotoxin fusion proteins

We investigated whether the toxicity‐associated receptor‐binding domain of the non‐immunogenic Escherichia coliheat‐stable enterotoxin (STh) as a fusion with a carrier protein and the inclusion of an appropriate spacer are critical factors for eliciting antibody responses against the native toxin. The immunological properties of three toxic and one non‐toxic fusion proteins, consisting of STh N‐terminally joined to the C‐terminus of the major subunit ClpG of E. coliCS31A fimbriae, were compared. In contrast to the non‐toxic hybrid STh with glycine and leucine simultaneously substituted for the receptor‐interacting Pro13and Ala14amino acids, the toxic chimeras responded by producing high serum levels of anti‐STh antibodies in immunized animals. On the other hand, only the toxic ClpG‐STh construct with the natural peptide 47KSGPESM53of Pro‐STh as spacer stimulated STh‐neutralizing responses against both native toxin and enterotoxigenic live E. colicells. Altogether, these findings suggest a close relationship between conformational similarity to the native structure of STh and the ability to elicit specific antibody responses against STh.