FNR protein

The transcription of nir and nor genes in P. stutzeri (Cuypers and Zumft, 1992, 1993) and P. aeruginosa (Zimmermann et al., 1991) would appear to be controlled in part by homologs of the Fnr protein of E. coli (Guest, 1992) which is a redox sensitive, transcriptional activator. Fnr boxes (binding sequences) are located upstream from norC, nirM and nirS. It is likely therefore that Fnr-like proteins participate in a regulatory mechanism which derepresses the synthesis... 

Figure 16-18 Mossbauer X-ray absorption spectra of iron-sulfur clusters. (See Chapter 23 for a brief description of the method.) Quadrupole doublets are indicated by brackets and isomer shifts are marked by triangles. (A) [Fe2S2]1+ cluster of the Rieske protein from Pseudomonas mendocina, at temperature T = 200 K. (B) [Fe3S4]1+ state of D. gigas ferre-doxin II, T = 90 K. (C) [Fe3S4]° state of D. gigas ferredoxin II, T = 15 K. (D) [Fe4S4]2+ cluster of E. coli FNR protein, T = 4.2 K. (E) [Fe4S4]1+ cluster of E. coli sulfite reductase, T = 110 K. From Beinert et al.260...

In the absence of 02 the E. coli FNR protein induces proteins of the anaerobic respiration pathways. Nitrate also has its own two-component system that senses nitrate availability and activates transcription of enzymes catalyzing nitrate respiration.162 An expanded two-component system induces sporulation in Bacillus subtilis in response to poor growth conditions.163164 The crystal structure of one of two response regulators (SpoOF) has a structure closely related to that of CheY and the nitrate response regulator NarL. 

M. P. Jennings and I. R. Beacham. Analysis of the Escherichia coli gene encoding 1-asparaginase II, ansB, and its regulation by cyclic AMP receptor and FNR proteins. J. BacterioL 772 1491 (1990). 

Figure 9-1A shows a Mossbauer spectrum of purified wild type FNR protein recorded in the absence of a magnetic field. The spectrum exhibits a single doublet with... 

Figure 9-1 (A) 4.2 K M5ssbauer spectra of an anaerobically purified FNR protein sample in the native state (B) after 17 minutes exposure to air, (C) after degassing and sodium dithionite treatment of the air-oxidized sample. The spectra were collected in a 4S mT magnetic field applied parallel to the incident y-radiation. The solid lines are spectral simulations obtained with the parameters listed in [6].

Figure 9-2 4.2 K Mossbauer spectra of the anaerobically purified FNR protein, after 17 minutes of exposure to air, recorded in (A)...

The present study demonstrates that the Mossbauer spectral signature of the FNR protein is readily recognizable in spectra of whole E. coli cells, provided this protein is over-expressed. Moreover, the approach used here may be applicable for probing other proteins in their native cellular environment. 

Note added in proof After the submission of this manuscript, we have completed a whole cells Mossbauer study of 4Fe — 2Fe cluster conversion in the FNR protein using a different set of samples. The results are published in Proc. Nat. Acad Sci. 1998, 95, 13431. 

First, the flexibility of the iron-sulfur center gives it the potential to exist under different [2Fe-2S], [3Fe-4S], [4Fe-4S] forms. Whether this has functional importance remains to be determined. Very recently the Fnr protein, the pyruvate formate lyase and the biotin synthase were shown to share this property [48-50]. Second, its reducing power allows it to inject electrons into protein-bound AdoMet, as a prerequisite for the formation of an essential glycyl radical. Third, this radical is used for ribose activation, by hydrogen atom abstraction. It is likely that this reaction is mediated by a cysteinyl radical [53]. Fourth, formate is used as the hydrogen donor for ribose reduction [38]. 

Another interesting example from E. coli is the FNR protein (Figure 17-14). FNR is also a transcription factor that toggles between inactive (oxidized) and... 

As predicted, based on DNA sequence homology [35], POR likely arose from the fusion of two ancestral genes related to the flavodoxin (Fid) and ferredoxin NADP rednctase (FNR) proteins. This hypothesis has snbseqnently been confirmed both by site-directed mntagenesis stndies and X-ray ciystallography [36], confirming the stmctural and catalytic functions of conserved residues. The domain organization of POR is apparent from the crystal stmcture of POR, exhibiting domains stmcturally related to flavodoxin... 

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