NfoR, Chromate Reductase or FMN reductase?
NfoR, Chromate Reductase or FMN reductase?
Appl Environ Microbiol. 2020 Sep 04;:
Authors: O'Neill AG, Beaupre BA, Zheng Y, Liu D, Moran GR
Abstract
Soil bacteria can detoxify Cr(VI) ions by reduction. Within the last two decades numerous reports of chromate reductase enzymes have been published. These reports purport 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 Staphlococcus aureus that was claimed to be upregulated in chromate rich soils and to have chromate reductase activity (Han H, Ling Z, Zhou T, Xu R, He Y, Liu P, Li X. 2017. Sci Rep 7:15481.). We show that NfoR has structural similarity to known 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 1350 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 slower than this process occurs in solution. We propose that NfoR is an FMN reductase and that the criterium required to define chromate reduction as enzymatic has not been met. That NfoR expression is increased in the presence of...
Source: Applied and Environmental Microbiology - Category: Microbiology Authors: O'Neill AG, Beaupre BA, Zheng Y, Liu D, Moran GR Tags: Appl Environ Microbiol Source Type: research