Determination of the amino acid change responsible for the nontoxic, cross-reactive exotoxin A protein (CRM 66) of Pseudomonas aeruginosa PAO-PR1

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Abstract
Analysis of purified exotoxin A from parental Pseudomonas aeruginosa PAO1 and mutant strain PAO-PR1, which produces enzymatically inactive exotoxin A (CRM 66), revealed that CRM 66 lost 90% of parental enzymatic activity. Nucleotide sequence analysis of cloned exotoxin A genes showed a single amino acid substitution in CRM 66. Position 426 in the mature protein of parental (PAO1) exotoxin A is histidine, whereas in CRM 66, it is tyrosine.