An oxygenase that forms and deoxygenates toxic epoxide

Area of Science:

• Biochemistry
• Microbiology
• Enzymology

Background:

• Bacterial catabolism of phenylacetic acid can produce toxic epoxide intermediates.
• The phenylacetyl-CoA monooxygenase (PaaABCE) complex is crucial for this pathway but poorly understood.
• This pathway is linked to the degradation of aromatics, metabolite production, and pathogen virulence.

Purpose of the Study:

• To characterize the bacterial multicomponent monooxygenase PaaABCE.
• To elucidate the mechanism of phenylacetyl-CoA epoxidation and subsequent deoxygenation.
• To investigate the enzyme complex's role in preventing toxic epoxide accumulation.

Main Methods:

• Biochemical characterization of the PaaABCE enzyme complex.
• Investigation of substrate transformation and cofactor dependency (NADPH).
• Structural and mechanistic studies to identify the catalytic center.

Main Results:

• PaaABCE epoxidizes phenylacetyl-CoA and subsequently deoxygenates the epoxide using NADPH, regenerating phenylacetyl-CoA.
• Evidence suggests a catalytic di-iron center responsible for the deoxygenation reaction.
• The enzyme complex exhibits bifunctional oxygenase/deoxygenase activity, acting as an intrinsic detoxification system.
• Associated thioesterases (PaaI and PaaY) further degrade toxic products.

Conclusions:

• PaaABCE is a novel bifunctional enzyme with an unprecedented deoxygenation capability.
• This enzyme complex provides an escape mechanism from its own toxic epoxide intermediates.
• PaaABCE represents a potential archetype for other di-iron epoxidases involved in detoxification.