Crystal Structure of PnpCD, a Two-subunit Hydroquinone 1,2-Dioxygenase, Reveals a Novel Structural Class of Fe2+-dependent Dioxygenases

Abstract

Background: Two-subunit hydroquinone 1,2-dioxygenase PnpCD is the ring cleavage enzyme in para-nitrophenol catabolism. Results:The structures of apo-PnpCD and its complex with substrate analog (hydroxybenzonitrile) were determined. Conclusion: PnpCD reveals a new class of Fe 2ϩ -dependent dioxygenases. Significance: PnpCD structure contains a pseudo "cupin" and a novel iron metallocenter in the catalytic PnpD, which adds to understanding of the ring cleavage mechanism of dioxygenases.

The molecular basis for the intramolecular migration (NIH shift) of the carboxyl group during para‐hydroxybenzoate catabolism

“…Aromatic compounds rank behind only carbohydrates as the most abundant class of organic compounds (Kluczek-Turpeinen et al, 2003;Fuchs et al, 2011) and most of them can be utilized by microorganisms (Harwood and Parales, 1996;Gibson and Harwood, 2002;Fuchs et al, 2011). The classical oxygen-dependent catabolism is initially catalyzed by mono-or dioxygenases that hydroxylate the aromatic ring to form activated intermediates, such as catechol (1, 2-dihydroxybenzene), protocatechuate (3, 4-dihydroxybenzoate), gentisate (GA, 2, 5-dihydroxybenzoate), hydroquinone and substituted hydroquinones for ring cleavage by their corresponding dioxygenases (Ornston and Stanier, 1966;Harwood and Parales, 1996;Fuchs et al, 2011;Hayes et al, 2013;Liu et al, 2015). Biodegradation pathways for many lignin breakdown products including biphenyl, vanillic acid, para-hydroxybenzoate (PHB), converge at these central intermediates which illustrates their key role in the global carbon cycle (Kosa and Ragauskas, 2013;Sainsbury et al, 2013).…”