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  • 1.
    Kahle, Maximilian
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    ter Beek, Josy
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Hosler, Jonathan P.
    Ädelroth, Pia
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    The insertion of the non-heme Fe-B cofactor into nitric oxide reductase from P. denitrificans depends on NorQ and NorD accessory proteins2018In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1859, no 10, p. 1051-1058Article in journal (Refereed)
    Abstract [en]

    Bacterial NO reductases (NOR) catalyze the reduction of NO into N2O, either as a step in denitrification or as a detoxification mechanism. cNOR from Paracoccus (P.) denitrificans is expressed from the norCBQDEF operon, but only the NorB and NorC proteins are found in the purified NOR complex. Here, we established a new purification method for the P. denitrificans cNOR via a His-tag using heterologous expression in E. coli. The His-tagged enzyme is both structurally and functionally very similar to non-tagged cNOR. We were also able to express and purify cNOR from the structural genes norCB only, in absence of the accessory genes norQDEF. The produced protein is a stable NorCB complex containing all hemes and it can bind gaseous ligands (CO) to heme b(3), but it is catalytically inactive. We show that this deficient cNOR lacks the nonheme iron cofactor Fe B . Mutational analysis of the nor gene cluster revealed that it is the norQ and norD genes that are essential to form functional cNOR. NorQ belongs to the family of MoxR P-loop AAA + ATPases, which are in general considered to facilitate enzyme activation processes often involving metal insertion. Our data indicates that NorQ and NorD work together in order to facilitate non-heme Fe insertion. This is noteworthy since in many cases Fe cofactor binding occurs spontaneously. We further suggest a model for NorQ/D-facilitated metal insertion into cNOR.

  • 2.
    ter Beek, Josy
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Krause, Nils
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Reimann, Joachim
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Lachmann, Peter
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Ädelroth, Pia
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    The Nitric-oxide Reductase from Paracoccus denitrificans Uses a Single Specific Proton Pathway2013In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 288, no 42, p. 30626-30635Article in journal (Refereed)
    Abstract [en]

    The NO reductase from Paracoccus denitrificans reduces NO to N2O (2NO + 2H(+) + 2e(-) → N2O + H2O) with electrons donated by periplasmic cytochrome c (cytochrome c-dependent NO reductase; cNOR). cNORs are members of the heme-copper oxidase superfamily of integral membrane proteins, comprising the O2-reducing, proton-pumping respiratory enzymes. In contrast, although NO reduction is as exergonic as O2 reduction, there are no protons pumped in cNOR, and in addition, protons needed for NO reduction are derived from the periplasmic solution (no contribution to the electrochemical gradient is made). cNOR thus only needs to transport protons from the periplasm into the active site without the requirement to control the timing of opening and closing (gating) of proton pathways as is needed in a proton pump. Based on the crystal structure of a closely related cNOR and molecular dynamics simulations, several proton transfer pathways were suggested, and in principle, these could all be functional. In this work, we show that residues in one of the suggested pathways (denoted pathway 1) are sensitive to site-directed mutation, whereas residues in the other proposed pathways (pathways 2 and 3) could be exchanged without severe effects on turnover activity with either NO or O2. We further show that electron transfer during single-turnover reduction of O2 is limited by proton transfer and can thus be used to study alterations in proton transfer rates. The exchange of residues along pathway 1 showed specific slowing of this proton-coupled electron transfer as well as changes in its pH dependence. Our results indicate that only pathway 1 is used to transfer protons in cNOR.

  • 3.
    ter Beek, Josy
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Krause, Nils
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Ädelroth, Pia
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Investigating the Proton Donor in the NO Reductase from Paracoccus denitrificans2016In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 3, article id e0152745Article in journal (Refereed)
    Abstract [en]

    Variant nomenclature: the variants were made in the NorB subunit if not indicated by the superscript(c), which are variants in the NorC subunit (e.g. E122A = exchange of Glu-122 in NorB for an Ala, E71(c)D; exchange of Glu-71 in NorC for an Asp). Bacterial NO reductases (NORs) are integral membrane proteins from the heme-copper oxidase superfamily. Most heme-copper oxidases are proton-pumping enzymes that reduce O-2 as the last step in the respiratory chain. With electrons from cytochrome c, NO reductase (cNOR) from Paracoccus (P.) denitrificans reduces NO to N2O via the following reaction: 2NO+2e(-)+2H(+) -> N2O+H2O. Although this reaction is as exergonic as O-2-reduction, cNOR does not contribute to the electrochemical gradient over the membrane. This means that cNOR does not pump protons and that the protons needed for the reaction are taken from the periplasmic side of the membrane (since the electrons are donated from this side). We previously showed that the P. denitrificans cNOR uses a single defined proton pathway with residues Glu-58 and Lys-54 from the NorC subunit at the entrance. Here we further strengthened the evidence in support of this pathway. Our further aim was to define the continuation of the pathway and the immediate proton donor for the active site. To this end, we investigated the region around the calcium-binding site and both propionates of heme b(3) by site directed mutagenesis. Changing single amino acids in these areas often had severe effects on cNOR function, with many variants having a perturbed active site, making detailed analysis of proton transfer properties difficult. Our data does however indicate that the calcium ligation sphere and the region around the heme b(3) propionates are important for proton transfer and presumably contain the proton donor. The possible evolutionary link between the area for the immediate donor in cNOR and the proton loading site (PLS) for pumped protons in oxygen-reducing heme-copper oxidases is discussed.

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