Localization of the diphtheria toxin receptor-binding domain to the carboxyl-terminal Mr approximately 6000 region of the toxin.

The carboxyl-terminal Mr = 5982 peptide of diphtheria toxin was prepared by specific cleavage of the toxin with hydroxylamine and purified by fast performance liquid chromatography. The identity of the peptide was established by a combination of sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis, reactivity with specific monoclonal antibodies, and amino-terminal sequence analysis. The Mr = 5982 peptide was shown to protect highly toxin-sensitive Vero cells from the lethal action of diphtheria toxin. This protection was shown to be due to inhibition of the initial step in the cytotoxic process, the binding of toxin to its receptor. These results strongly suggest that the Mr = 5982 carboxyl-terminal region (amino acid residues 482-535) is, or contains, the receptor-binding domain of diphtheria toxin.