Abstract
Escherichia coli amine oxidase (ECAO), encoded by the tynA gene, catalyzes the oxidative deamination of aromatic amines into aldehydes through a well-established mechanism, but its exact biological role is unknown. We investigated the role of ECAO by screening environmental and human isolates for tynA and characterizing a tynA-deletion strain using microarray analysis and biochemical studies. The presence of tynA did not correlate with pathogenicity. In tynA+ Escherichia coli strains, ECAO enabled bacterial growth in phenylethylamine, and the resultant H2O2 was released into the growth medium. Some aminoglycoside antibiotics inhibited the enzymatic activity of ECAO, which could affect the growth of tynA+ bacteria. Our results suggest that tynA is a reserve gene used under stringent environmental conditions in which ECAO may, due to its production of H2O2, provide a growth advantage over other bacteria that are unable to manage high levels of this oxidant. In addition, ECAO, which resembles the human homolog hAOC3, is able to process an unknown substrate on human leukocytes.
Highlights
Primary amine oxidases (EC 1.4.3.21, PrAOs, known as copper-containing amine oxidases, copper amine oxidase (CAO)) are expressed in mammals, plants, and bacteria
We found that Escherichia coli amine oxidase (ECAO) can utilize a human leukocyte cell surface molecule(s) as a substrate and is inhibited by a hAOC3 inhibitor, which suggests that it shares similarities to its human counterpart
The subsequent screening of different human isolates and E. coli pathotypes indicated that this gene could be frequently detected in diarrhea-causing pathotypes, such as non-O157: H7 enterohemorrhagic E. coli (EHEC) (82% tynA+), enterotoxigenic E. coli (ETEC; 69%), and enteroinvasive E. coli (EIEC; 67%), as well as in fecal isolates (38%, Table 2)
Summary
Primary amine oxidases (EC 1.4.3.21, PrAOs, known as copper-containing amine oxidases, CAOs) are expressed in mammals, plants, and bacteria. These enzymes catalyze the oxidation of primary amines into aldehyde through the reaction R-CH2-NH2 + O2 + H2O ! The preferred amine substrate depends on the specific amine oxidase, and the aldehyde product depends on the substrate [1]. The by-products of the reaction, hydrogen peroxide and ammonia, are invariably released.
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