Expression of a neutral horseradish peroxidase in Escherichia coli

A cDNA sequence encoding a neutral horseradish peroxidase, HRP-n, was found to be growth inhibiting and under certain circumstances also toxic to Escherichia coli upon expression. The growth inhibiting and toxic activity was identified to a sequence of 192 nucleotides which encode the first deduced 64 N-terminal amino acids of the total 299 amino acids in the mature, neutral horseradish peroxidase. The sequence makes part of the active site of the enzyme and is very conserved among peroxidases. The cDNA sequence was cloned in the heat inducible expression vector pJLA603. The toxic effect was mediated by the produced polypeptide since no growth inhibiting or toxic activity was observed when the cDNA sequence was induced after ligation in a wrong reading frame. Generation of oxygen radicals was not the mechanism behind the toxicity, since the effect was observed even after induction of the complete HRP-n sequence or the identified toxic sequence under anaerobic conditions.