Spectroscopic Characterisation of the Naphthalene Dioxygenase from Rhodococcus sp. Strain NCIMB12038

Abstract

Polycyclic aromatic hydrocarbons (PAHs), such as naphthalene, are potential health risks due to their carcinogenic and mutagenic effects. Bacteria from the genus Rhodococcus are able to metabolise a wide variety of pollutants such as alkanes, aromatic compounds and halogenated hydrocarbons. A naphthalene dioxygenase from Rhodococcus sp. strain NCIMB12038 has been characterised for the first time, using electron paramagnetic resonance (EPR) spectroscopy and UV-Vis spectrophotometry. In the native state, the EPR spectrum of naphthalene 1,2-dioxygenase (NDO) is formed of the mononuclear high spin Fe(III) state contribution and the oxidised Rieske cluster is not visible as EPR-silent. In the presence of the reducing agent dithionite a signal derived from the reduction of the [2Fe-2S] unit is visible. The oxidation of the reduced NDO in the presence of O2-saturated naphthalene increased the intensity of the mononuclear contribution. A study of the “peroxide shunt”, an alternative mechanism for the oxidation of substrate in the presence of H2O2, showed catalysis via the oxidation of mononuclear centre while the Rieske-type cluster is not involved in the process. Therefore, the ability of these enzymes to degrade recalcitrant aromatic compounds makes them suitable for bioremediative applications and synthetic purposes.

Carnitine metabolism in the human gut: characterization of the two-component carnitine monooxygenase CntAB from Acinetobacter baumannii

“…A strong S = 5/2 signal with a g value of g = 4.27 was observed which is characteristic for the presence of a mononuclear iron (III) center. Conversion of such Fe center into the EPR silent iron (II) state can be accomplished upon chemical reduction (36).…”

Two-component carnitine monooxygenase from Escherichia coli: functional characterization, inhibition and mutagenesis of the molecular interface

“…A S = 5/2 signal of a mononuclear iron (III) center with a g -value of 4.310 was observed. Dithionite reduction resulted in a bleaching of the protein sample ( Figure 4 B, dashed trace) and the [Fe] center of YeaW was converted into the EPR silent iron (II) state [ 28 ]. In parallel, appearance of a S = 1/2 signal with g -values of g 1 = 2.016, g 2 = 1.920 and g 3 = 1.749 ( Figure 4 C, bottom) was observed, which is characteristic for the presence of a [2Fe-2S] + center of the Rieske-type [ 29 ].…”

“…Dithionite reduction resulted in a bleaching of the protein sample (Fig. 4B, dashed trace) and the [Fe] center of YeaW was converted into the EPR silent iron (II) state (28). In parallel, appearance of a S = 1/2 signal with g-values of g 1 = 2.016, g 2 = 1.920 and g 3 = 1.749 (Fig.…”

Understanding the stability of a plastic‐degrading Rieske iron oxidoreductase system

“…The coordination state of the mononuclear iron then shifts from square pyramidal to trigonal bipyramidal. (Baratto et al, 2019 ; Ohta et al, 2008 ; Wolfe et al, 2002 ; Wolfe & Lipscomb, 2003 ), resulting in a more tightly bound metal. We noted a greater susceptibility toward chelation of the mononuclear Fe versus the Rieske cofactor (Figures S9 and S10 ).…”