Relationship of primary structure to functional properties of the cytotoxin protein from Pseudomonas aeruginosa

Deletion mutants of plasmid pSN3 carrying the Pseudomonas aeruginosa cytotoxin gene were prepared and expression in Escherichia coli of proteins with different molecular weights has been proved by Western blot. In addition, through PCR amplification of the cytotoxin gene and ligation into the vector, a single nucleotide change leading to an amino acid exchange from histidine to arginine has been constructed. The activities of the mutants were tested by binding of 125I-cytotoxin to rabbit erythrocyte ghosts and swelling of human granulocytes, showing that the cytotoxin activity is dependent on at least three different domains. Amino acids 12-20 from the C-terminus might be very important for proteolytic activation of protoxin to toxin.