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An oxygenase that forms and deoxygenates toxic epoxide


Catabolism may give rise to toxic intermediates that compromise cell vitality, such as epoxide formation in the recently elucidated and apparently universal bacterial coenzyme A (CoA)-dependent degradation of phenylacetic acid1. This compound is central to the catabolism of a variety of aromatics, such as phenylalanine, lignin-related compounds or environmental contaminants2,3. The key phenylacetyl-CoA monooxygenase (epoxidase) of the pathway, PaaABCE1,4,5, is also connected to the production of various primary and secondary metabolites6,7,8,9, as well as to the virulence of certain pathogens1,10,11. However, the enzyme complex has so far not been investigated in detail. Here we characterize the bacterial multicomponent monooxygenase PaaABCE that, surprisingly, not only transforms phenylacetyl-CoA into its ring-1,2-epoxide, but also mediates the NADPH-dependent removal of the epoxide oxygen, regenerating phenylacetyl-CoA with formation of water. We provide evidence for a catalytic di-iron centre that is probably the key to the unprecedented deoxygenation of an organic compound by an oxygenase. Presumably, the bifunctionality is vital to avoid toxic intracellular epoxide levels if the subsequent catabolic steps are impeded. Our data suggest that detoxification is assisted by two thioesterases (PaaI and PaaY) forming non-reactive breakdown products. Hence, PaaABCE may harbour an intrinsic escape mechanism from its own toxic product and represents the archetype of a bifunctional oxygenase/deoxygenase. Analogous reactions may possibly be catalysed by other di-iron epoxidases.

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Figure 1: Overview of reactions and proposed salvage reactions of phenylacetate degradation.
Figure 2: PaaABCE is a bifunctional monooxygenase/deoxygenase.
Figure 3: Simplified scheme of proposed reactions catalysed by PaaABCE and states of the catalytic di-iron centre.

Accession codes

Data deposits

For E. coli K12, the NCBI database accession numbers are as follows: PaaY, NP_415918.1; PaaI, NP_415914.1. For Pseudomonas sp. strain Y2, the EMBL database numbers are as follows: PaaA, CAD76929.1; PaaB, CAD76932.1; PaaC, CAD76933.1; PaaD, CAD76935.1; PaaE, CAD76937.1.


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We thank Deutsche Forschungsgemeinschaft for support; V. Mascaraque, G. Heijman and W. Ismail for their contributions in the initial stage of this work; M. Voss, M. Weiß, I. Sachelaru and T. Spatzal for technical assistance; M. Müller and V. Brecht for mass spectrometry analysis; and I. Berg and H. Heider for critical comments.

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Authors and Affiliations



R.T. and T.F. performed research; R.T, T.F. and G.F designed research and analysed data; and R.T. and G.F. wrote the paper.

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Correspondence to Georg Fuchs.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Figures 1-11, Supplementary Tables 1-4, a Supplementary Discussion and additional references. Supplementary Figure 11 shows PaaZ inhibition by the derivative and Supplementary Table 4 substrate specificity of thioesterases PaaI and PaaY. (PDF 2463 kb)

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Teufel, R., Friedrich, T. & Fuchs, G. An oxygenase that forms and deoxygenates toxic epoxide. Nature 483, 359–362 (2012).

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