Exotoxin A of Pseudomonas aeruginosa: evidence that Domain I functions In receptor binding

We have constructed defined deletions in the structural gene of Pseudomonas aeruginosa exotoxin A (ETA) in order to probe the function of Domain I of this protein. Three forms of the gene containing specific deletions were expressed in a strain of Escherichia coli K12 with lesions in the htpR and Ion genes; extracts containing the gene products were tested for ADP-ribosylation activity, cytotoxicity, and ability to protect sensitive cells from the cytotoxic action of authentic ETA. Two of the mutant ETAs gave concentration-dependent protection against authentic ETA, and protection correlated with the presence of the bulk of Domain I. The results support the notion that Domain I functions in binding the toxin to specific cell-surface receptors.