IngentaConnect GlnK effects complex formation between NifA and NifL in Klebsiell...

Authors: Stips, Jessica; Thummer, Robert; Neumann, Melanie; Schmitz, Ruth A.

Source: FEBS Journal, Volume 271, Number 16, August 2004 , pp. 3379-3388(10)

Abstract:

In Klebsiella pneumoniae, the nif specific transcriptional activator NifA is inhibited by NifL in response to molecular oxygen and ammonium. Here, we demonstrate complex formation between NifL and NifA (approximately 1 : 1 ratio), when synthesized in the presence of oxygen and/or ammonium. Under simultaneous oxygen- and nitrogen-limitation, significant but fewer NifL-NifA complexes (approximately 1%) were formed in the cytoplasm as a majority of NifL was sequestered to the cytoplasmic membrane. These findings indicate that inhibition of NifA in the presence of oxygen and/or ammonium occurs via direct NifL interaction and formation of those inhibitory NifL-NifA complexes appears to be directly and exclusively dependent on the localization of NifL in the cytoplasm. We further observed evidence that the nitrogen sensory protein GlnK forms a trimeric complex with NifL and NifA under nitrogen limitation. Binding of GlnK to NifL-NifA was specific; however the amount of GlnK within these complexes was small. Finally, two lines of evidence were obtained that under anaerobic conditions but in the presence of ammonium additional NtrC-independent GlnK synthesis inhibited the formation of stable inhibitory NifL-NifA complexes. Thus, we propose that the NifL-NifA-GlnK complex reflects a transitional structure and hypothesize that under nitrogen-limitation, GlnK interacts with the inhibitory NifL-NifA complex, resulting in its dissociation.

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GlnK effects complex formation between NifA and NifL in Klebsiella pneumoniae