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Review
. 2004 Feb;186(3):601-10.
doi: 10.1128/JB.186.3.601-610.2004.

The NifL-NifA System: a multidomain transcriptional regulatory complex that integrates environmental signals

Isabel Martinez-Argudo  1 , Richard Little, Neil Shearer, Philip Johnson, Ray Dixon
Affiliations
Review

The NifL-NifA System: a multidomain transcriptional regulatory complex that integrates environmental signals

Isabel Martinez-Argudo et al. J Bacteriol. 2004 Feb.
No abstract available

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Figures

FIG. 1.
FIG. 1.
Graphic view of the domain structure of Av NifL (NIFL_AZOVI) and Kp NifL (NIFL_KLEPN) from the INTERPRO server (http://www.ebi.ac.uk/interpro/). INTERPRO assignments and database cross-references are indicated on the left, and the corresponding domains are indicated on the right. Domain designations used in this paper are above the diagram. PAS domains are subdivided into PAS and PAC motifs in some databases (78), but both of these motifs form an integral part of a single structural domain. The term PAS domain in this paper refers to the single structural fold that encompasses both the PAS and PAC motifs.
FIG. 2.
FIG. 2.
Cascade regulation of nif genes in K. pneumoniae in response to the fixed nitrogen status. Under nitrogen-limiting conditions, GlnB is uridylylated and NtrB phosphorylates NtrC, leading to activation of transcription of the glnK, amtB, and nifLA operons. Expression of GlnK prevents Kp NifL from inhibiting Kp NifA, leading to activation of nif transcription. Under nitrogen-sufficient conditions, GlnD deuridylylates GlnB, which is then competent to activate the phosphatase activity of NtrB; this limits the availability of NtrC-P and prevents expression of nifLA and glnK amtB. Following ammonium upshift GlnK may be sequestered by AmtB, as discussed in the text.
FIG. 3.
FIG. 3.
Nitrogen source regulation of nif gene transcription in A. vinelandii. Under conditions of fixed-nitrogen limitation (−N), GlnK is mainly uridylylated and not competent to interact with NifL. Under these conditions, binding of 2-oxoglutarate to the GAF domain of Av NifA relieves inhibition by Av NifL, freeing NifA to activate transcription. Under conditions of fixed-nitrogen sufficiency (+N), GlnD deuridylylates GlnK, which interacts with NifL, promoting formation of the NifL-NifA complex.
FIG. 4.
FIG. 4.
Model showing potential interactions between Av NifL and Av NifA in response to environmental cues. Only the PAS1 and ADP binding domains of NifL are shown (open and cross-hatched ovals, respectively). The three domains of Av NifA are labeled GAF, AAA, and HTH. Under nitrogen-limiting conditions GlnK is uridylylated, and provided that the flavin moiety in Av NifL is reduced, Av NifA is free to activate transcription, catalyzed by ATP hydrolysis (center diagram). However, when Av NifL is oxidized, the NifL-NifA binary complex is formed, perhaps promoted by conformational changes mediated via the PAS domain. Formation of the complex sequesters Av NifA, preventing transcriptional activation. Under nitrogen-excess conditions, when GlnK is in the noncovalently modified form, it interacts with the C-terminal ADP binding domain of Av NifL to promote formation of a ternary complex in which the activity of Av NifA is also inhibited.
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References

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