KatP, a novel catalase-peroxidase encoded by the large plasmid of enterohaemorrhagic Escherichia coli O157:H7

Abstract

A gene coding for a catalase-peroxidase activity was identified on a 9-7 kb Smal DNA fragment derived from the large plasmid pO157 of enterohaemorrhagic Escherichia coli (EHEC) O157:H7 strain EDL 933. Nucleotide sequencing revealed an ORF of 2208 bp and predicted a 736 amino acid polypeptide with a molecular mass of 81.8 kDa. This putative protein was found to be highly homologous to members of the bacterial bifunctional catalase-peroxidase family. Analysis of its amino acid sequence revealed the presence of characteristic peroxidase 1 and 2 motifs. In addition, an N-terminal signal sequence was found, suggesting that the catalase-peroxidase is transported through the cytoplasmic membrane. EHEC catalase-peroxidase activities were investigated in cytoplasmic and periplasmic crude extracts as well as in culture supernatants from wild-type and recombinant E. coli strains. EHEC-specific catalase-peroxidase activity was detected primarily in the periplasm in strain EDL 933. The newly discovered enzyme was designated KatP, to indicate its plasmid origin. PCR analysis of representative strains of all enteric E. coli pathogroups (i.e. enterohaemorrhagic, enterotoxigenic, enteropathogenic, enteroaggregative and enteroinvasive E. coli) revealed a close association between the occurrence of EHEC-haemolysin and the katP gene in Shiga-like-toxin-producing E. coli O157 strains.