tailieunhanh - Báo cáo khoa học: GlnK effects complex formation between NifA and NifL in Klebsiella pneumoniae

In Klebsiella pneumoniae,the nif specific transcriptional activator NifA is inhibited byNifL in response tomolecular 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 mem-brane. | Eur. J. Biochem. 271 3379-3388 2004 FEBS 2004 doi GlnK effects complex formation between NifA and NifL in Klebsiella pneumoniae Jessica Stips Robert Thummer Melanie Neumann and Ruth A. Schmitz Institut fur Mikrobiologie und Genetik Gottingen Germany 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 nitrogenlimitation 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. Keywords Klebsiella pneumoniae nitrogen fixation NifL NifA GlnK. Nitrogen-fixing microorganisms tightly control both synthesis and activity of nitrogenase in response to oxygen and nitrogen availability because of the high energy demands of nitrogen fixation and the oxygen .