Engineering of cholera toxin A-subunit for carriage of epitopes at its amino end

The cholera toxin A-subunit (CTA) was genetically engineered at its amino end and tested for carriage of epitopes by fusion of the STa heat-stable enterotoxin analogue CAELCCNPAC. Efficient holotoxin formation by complementation in trans with cholera toxin B-subunit (CTB) indicated no decrease in affinity for CTB but evidence of reduced toxicity suggests steric interference by the decapeptide with the active site. The holotoxin was stable, able to bind to GM1 and was recognized by anti-STa and anti-CTA antibodies. The use of a full-length CTA might have been a key step for successful genetic fusions. Based on these findings, it seems worthwhile pursue the development of CTA for construction of recombinant mucosal immunoadjuvants.