The Moraxella catarrhalis Nitric Oxide Reductase Is Essential for Nitric Oxide Detoxification

The identification of nitric oxide-bound leghaemoglobin within soya bean nodules has led to the question of how Bradyrhizobium japonicum bacteroids overcome the toxicity of this nitric oxide. It has previously been shown that one candidate for nitric oxide detoxification, the respiratory nitric oxide reductase, is expressed in soya bean nodules from plants supplied with nitrate [Mesa, de Dios Alché, Bedmar and Delgado (2004) Physiol. Plant. 120, 205–211]. In this paper, the role of this enzyme in nitric oxide detoxification is assessed and discussion is provided on other possible B. japonicum nitric oxide detoxification systems.

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Kinetic and thermodynamic resolution of the interactions between sulfite and the pentahaem cytochrome NrfA from Escherichia coli

Biochemical Journal ◽

10.1042/bj20100866 ◽

2010 ◽

Vol 431 (1) ◽

pp. 73-80 ◽

Cited By ~ 28

Author(s):

Gemma L. Kemp ◽

Thomas A. Clarke ◽

Sophie J. Marritt ◽

Colin Lockwood ◽

Susannah R. Poock ◽

...

Keyword(s):

Nitric Oxide ◽

Escherichia Coli ◽

Active Site ◽

Dissociation Constants ◽

Cellular Activity ◽

Nitric Oxide Reductase ◽

Wide Range ◽

Nitric Oxide Reduction ◽

Nitric Oxide Detoxification ◽

Kinetic And Thermodynamic Studies

NrfA is a pentahaem cytochrome present in a wide-range of γ-, δ- and ε-proteobacteria. Its nitrite and nitric oxide reductase activities have been studied extensively and contribute to respiratory nitrite ammonification and nitric oxide detoxification respectively. Sulfite is a third substrate for NrfA that may be encountered in the micro-oxic environments where nrfA is expressed. Consequently, we have performed quantitative kinetic and thermodynamic studies of the interactions between sulfite and Escherichia coli NrfA to provide a biochemical framework from which to consider their possible cellular consequences. A combination of voltammetric, spectroscopic and crystallographic analyses define dissociation constants for sulfite binding to NrfA in oxidized (~54 μM), semi-reduced (~145 μM) and reduced (~180 μM) states that are comparable with each other, and the Km (~70 μM) for sulfite reduction at pH 7. Under comparable conditions Km values of ~22 and ~300 μM describe nitrite and nitric oxide reduction respectively, whereas the affinities of nitrate and thiocyanate for NrfA fall more than 50-fold on enzyme reduction. These results are discussed in terms of the nature of sulfite co-ordination within the active site of NrfA and their implications for the cellular activity of NrfA.

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Identification of a Repressor of a Truncated Denitrification Pathway in Moraxella catarrhalis

Journal of Bacteriology ◽

10.1128/jb.01032-08 ◽

2008 ◽

Vol 190 (23) ◽

pp. 7762-7772 ◽

Cited By ~ 23

Author(s):

Wei Wang ◽

Anthony R. Richardson ◽

Willm Martens-Habbena ◽

David A. Stahl ◽

Ferric C. Fang ◽

...

Keyword(s):

Nitric Oxide ◽

Microarray Analysis ◽

Dna Microarray ◽

Moraxella Catarrhalis ◽

Open Reading Frames ◽

Nitric Oxide Reductase ◽

Wild Type ◽

Dna Microarray Analysis ◽

Inhibition Of Growth ◽

Reading Frames

ABSTRACT Growth of Moraxella catarrhalis in a biofilm resulted in marked upregulation of two open reading frames (ORFs), aniA and norB, predicted to encode a nitrite reductase and a nitric oxide reductase, respectively (W. Wang, L. Reitzer, D. A. Rasko, M. M. Pearson, R. J. Blick, C. Laurence, and E. J. Hansen, Infect. Immun. 75:4959-4971, 2007). An ORF designated nsrR, which was located between aniA and norB, was shown to encode a predicted transcriptional regulator. Inactivation of nsrR resulted in increased expression of aniA and norB in three different M. catarrhalis strains, as measured by both DNA microarray analysis and quantitative reverse transcriptase PCR. Provision of a wild-type nsrR gene in trans in an nsrR mutant resulted in decreased expression of the AniA protein. DNA microarray analysis revealed that two other ORFs (MC ORF 683 and MC ORF 1550) were also consistently upregulated in an nsrR mutant. Consumption of both nitrite and nitric oxide occurred more rapidly with cells of an nsrR mutant than with wild-type cells. However, growth of nsrR mutants was completely inhibited by a low level of sodium nitrite. This inhibition of growth by nitrite was significantly reversed by introduction of an aniA mutation into the nsrR mutant and was completely reversed by the presence of a wild-type nsrR gene in trans. NsrR regulation of the expression of aniA was sensitive to nitrite, whereas NsrR regulation of norB was sensitive to nitric oxide.

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