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NfoR: Chromate Reductase or Flavin Mononucleotide Reductase?

Journal Article · · Applied and Environmental Microbiology
DOI:https://doi.org/10.1128/aem.01758-20· OSTI ID:1729700
 [1];  [1];  [1];  [1];  [1]
  1. Loyola Univ. Chicago, IL (United States)
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Soil bacteria can detoxify Cr(VI) ions by reduction. Within the last 2 decades, numerous reports of chromate reductase enzymes have been published. These reports describe catalytic reduction of chromate ions by specific enzymes. These enzymes each have sequence similarity to known redox-active flavoproteins. We investigated the enzyme NfoR from Staphylococcus aureus, which was reported to be upregulated in chromate-rich soils and to have chromate reductase activity (H. Han, Z. Ling, T. Zhou, R. Xu, et al., Sci Rep 7:15481, 2017, https://doi.org/10.1038/s41598-017-15588-y). We show that NfoR has structural similarity to known flavin mononucleotide (FMN) reductases and reduces FMN as a substrate. NfoR binds FMN with a dissociation constant of 0.4 μM. The enzyme then binds NADPH with a dissociation constant of 140 μM and reduces the flavin at a rate of 1,350 s-1. Turnover of the enzyme is apparently limited by the rate of product release that occurs, with a net rate constant of 0.45 s-1. The rate of product release limits the rate of observed chromate reduction, so the net rate of chromate reduction by NfoR is orders of magnitude lower than when this process occurs in solution. We propose that NfoR is an FMN reductase and that the criterion required to define chromate reduction as enzymatic has not been met. That NfoR expression is increased in the presence of chromate suggests that the survival adaption was to increase the net rate of chromate reduction by facile, adventitious redox processes.
Research Organization:
Argonne National Laboratory (ANL), Argonne, IL (United States)
Sponsoring Organization:
USDOE
Contributing Organization:
Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
OSTI ID:
1729700
Journal Information:
Applied and Environmental Microbiology, Journal Name: Applied and Environmental Microbiology Journal Issue: 22 Vol. 86; ISSN 0099-2240
Publisher:
American Society for MicrobiologyCopyright Statement
Country of Publication:
United States
Language:
ENGLISH

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