Comparative immunochemistry of two fragments from domains Ib and III of Pseudomonas aeruginosa exotoxin A.

Two rabbit polyclonal antisera have been produced by immunization with two fragments corresponding to sequences 392 to 404 and 392 to 613 of Pseudomonas aeruginosa exotoxin A. Both antisera inhibit the ADP-ribosyltransferase activity of exotoxin A but do not inhibit its NAD-glycohydrolase activity. In addition, only the second antiserum was capable of neutralizing exotoxin A cytotoxicity in cell culture and in vivo. Consequently, the common sequence 392 to 404 of the two fragments is not a neutralizing epitope and such an epitope should reside within residues 405 to 613 of exotoxin A. The sequence 392 to 404 was shown to be hidden in the native molecule, and the results suggest that this sequence is most likely in close proximity to residues involved in eukaryotic elongation factor 2 binding.