Dataset Information

Multiple forms of the catalytic centre, CuZ, in the enzyme nitrous oxide reductase from Paracoccus pantotrophus.

ABSTRACT: Nitrous oxide reductase catalyses the reduction of nitrous oxide to dinitrogen at a unique tetranuclear copper site, called Cu(Z), which has a central inorganic sulphide ligand. Limited incubation with oxygen during the preparation of nitrous oxide reductase from Paracoccus pantotrophus results in changed redox properties of the catalytic centre by comparison with anaerobic preparations. While the anaerobically purified enzyme has a catalytic centre which performs a single electron step at a midpoint potential of E(m)=+60 mV versus the standard hydrogen electrode (n=1), the altered centre shows no redox change under similar experimental conditions. Spectroscopic properties of this 'redox fixed' centre are similar to spectra of the reduced 'redox active' form of CuZ, although the positions and intensities of a number of transitions are changed in the optical spectrum. These observations are interpreted in terms of two forms of the catalytic centre, called CuZ and CuZ*. The structural relationship between these forms is unclear. EPR and magnetic circular dichroism spectra suggest that the basic Cu4S structure is common to both. Curiously, steady-state activity of the aerobic enzyme preparation is slightly increased despite the fact the catalytic centre does not undergo detectable redox changes.

SUBMITTER: Rasmussen T

PROVIDER: S-EPMC1222630 | biostudies-other | 2002 Jun

REPOSITORIES: biostudies-other

ACCESS DATA

Similar Datasets

Project description:N2O is generated by denitrifying bacteria as a product of NO reduction. In denitrification, N2O is metabolized further by the enzyme N2O reductase (N2OR), a multicopper protein which converts N2O into dinitrogen and water. The structure of N2OR remained unknown until the recent elucidation of the structure of the enzyme isolated from Pseudomonas nautica. In the present paper, we report the crystal structure of a blue form of the enzyme that was purified under aerobic conditions from Paracoccus denitrificans. N2OR is a head-to-tail homodimer stabilized by a multitude of interactions including two calcium sites located at the intermonomeric surface. Each monomer is composed of two domains: a C-terminal cupredoxin domain that carries the dinuclear electron entry site known as Cu(A), and an N-terminal seven-bladed beta-propeller domain which hosts the active-site centre Cu(Z). The electrons are transferred from Cu(A) to Cu(Z) across the subunit interface. Cu(Z) is a tetranuclear copper cluster in which the four copper ions (Cu1 to Cu4) are ligated by seven histidine imidazoles, a hydroxyl or water oxygen and a bridging inorganic sulphide. A bound chloride ion near the Cu(Z) active site shares one of the ligand imidazoles of Cu1. This arrangement probably influences the redox potential of Cu1 so that this copper is stabilized in the cupric state. The treatment of N2OR with H2O2 or cyanide causes the disappearance of the optical band at 640 nm, attributed to the Cu(Z) centre. The crystal structure of the enzyme soaked with H2O2 or cyanide suggests that an average of one copper of the Cu(Z) cluster has been lost. The lowest occupancy is observed for Cu3 and Cu4. A docking experiment suggests that N(2)O binds between Cu1 and Cu4 so that the oxygen of N2O replaces the oxygen ligand of Cu4. Certain ligand imidazoles of Cu1 and Cu2, as well as of Cu4, are located at the dimer interface. Particularly those of Cu2 and Cu4 are parts of a bonding network which couples these coppers to the Cu(A) centre in the neighbouring monomer. This structure may provide an efficient electron transfer path for reduction of the bound N2O.

Dataset Information

Multiple forms of the catalytic centre, CuZ, in the enzyme nitrous oxide reductase from Paracoccus pantotrophus.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets