Cyanobacterial response regulator PatA contains a conserved N-terminal domain (PATAN) with an alpha-helical insertion (original) (raw)
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Molecular Microbiology, 2006
The heterocyst is a specialized cell for nitrogen fixation in the filamentous cyanobacteria, and its development is triggered by limitation of combined nitrogen in the medium. During heterocyst development, patterns of gene expression change dramatically. We identified seven genes encoding transcriptional regulators that were upregulated by nitrogen deprivation in Anabaena PCC 7120, using an Anabaena oligonucleotide microarray. Among them, the nrrA gene, which encodes a response regulator of the OmpR family with a DNA-binding domain, has shown the most prominent induction after nitrogen deprivation. Expression of nrrA increased all through the filaments within 3 h of nitrogen deprivation and became higher in proheterocysts than in vegetative cells after 12 h. Sequence analysis of the promoter region of nrrA indicated that the induction of nrrA depended on NtcA, which is the global nitrogen regulator in cyanobacteria. In the nrrA deletion mutant, heterocyst development was delayed and the induction of hetR , which is the master gene in regulation of heterocyst development, was diminished up to 24 h nitrogen deprivation. It is concluded that nrrA facilitates heterocyst development.
Frontiers in Microbiology, 2016
Cyanobacteria, phototrophic organisms that perform oxygenic photosynthesis, perceive nitrogen status by sensing 2-oxoglutarate levels. PII, a widespread signaling protein, senses and transduces nitrogen and energy status to target proteins, regulating metabolism and gene expression. In cyanobacteria, under conditions of low 2-oxoglutarate, PII forms complexes with the enzyme N-acetyl glutamate kinase, increasing arginine biosynthesis, and with PII-interacting protein X (PipX), making PipX unavailable for binding and co-activation of the nitrogen regulator NtcA. Both the PII-PipX complex structure and in vivo functional data suggested that this complex, as such, could have regulatory functions in addition to PipX sequestration. To investigate this possibility we performed yeast three-hybrid screening of genomic libraries from Synechococcus elongatus PCC7942, searching for proteins interacting simultaneously with PII and PipX. The only prey clone found in the search expressed PlmA, a member of the GntR family of transcriptional regulators proven here by gel filtration to be homodimeric. Interactions analyses further confirmed the simultaneous requirement of PII and PipX, and showed that the PlmA contacts involve PipX elements exposed in the PII-PipX complex, specifically the C-terminal helices and one residue of the tudor-like body. In contrast, PII appears not to interact directly with PlmA, possibly being needed indirectly, to induce an extended conformation of the C-terminal helices of PipX and for modulating the surface polarity at the PII-PipX boundary, two elements that appear crucial for PlmA binding. Attempts to inactive plmA confirmed that this gene is essential in S. elongatus. Western blot assays revealed that S. elongatus PlmA, irrespective of the nitrogen regime, is a relatively abundant transcriptional regulator, suggesting the existence of a large PlmA regulon. In silico studies showed that PlmA is universally and exclusively found in cyanobacteria. Based on interaction data, on the relative amounts of the proteins involved in PII-PipX-PlmA complexes, determined in western assays, and on the restrictions imposed by the symmetries of trimeric PII and dimeric PlmA molecules, a structural and regulatory model for PlmA function is discussed in the context of the cyanobacterial nitrogen interaction network.
Microbiology, 2010
Heterocyst-forming cyanobacteria are able to perform oxygenic photosynthesis and nitrogen fixation simultaneously in the same filament, by restricting the highly O 2-sensitive nitrogenase to specialized cells, the heterocysts. A remarkable change in morphology and metabolism accompanies the differentiation of heterocysts, which only occurs when no source of combined nitrogen is available. In this study, we characterized DevT (Alr4674), a putative protein phosphatase from Anabaena PCC 7120. Mutants defective in devT are able to form morphologically mature heterocysts, which however cannot fix N 2 , and the mutant cannot survive without a source of combined nitrogen. DevT shows homology to phosphatases of the PPP family and displays a Mn 2+-dependent phosphatase activity that can be inhibited by phosphatase inhibitors and oxidizing conditions. DevT is constitutively expressed in both vegetative cells and heterocysts, and is not regulated by NtcA. The heterocyst regulator HetR may exert a certain inhibition on the expression of devT. Under diazotrophic growth conditions, DevT protein accumulates specifically in mature heterocysts. Therefore DevT plays a still unknown role in a late essential step of heterocyst differentiation.
Journal of Bacteriology, 2006
Heterocyst differentiation in the cyanobacterium Anabaena sp. strain PCC 7120 requires NtcA, the global nitrogen regulator in cyanobacteria, and HetR, the master regulator of heterocyst differentiation. Expression of hetR is upregulated by nitrogen deprivation, and its upregulation depends on NtcA. However, it has not yet been revealed how NtcA regulates the expression of hetR. In the experiments presented here, it was confirmed that NrrA (All4312), a nitrogen-responsive response regulator, was required for the upregulation of hetR. The use of the nitrogen-responsive transcription initiation sites (TISs) for the hetR gene depended upon NrrA. NrrA bound specifically to the region upstream of TISs located at positions ؊728 and ؊696 in vitro. Overexpression of nrrA resulted in enhanced hetR expression and heterocyst formation. A molecular regulatory cascade is proposed whereby NtcA upregulates the expression of nrrA upon limitation of combined nitrogen in the medium and then NrrA upregulates the expression of hetR, leading to heterocyst differentiation.
Molecular Microbiology, 2010
Heterocysts are terminally differentiated cells that fix nitrogen in filaments of the cyanobacterium Anabaena PCC 7120. They differentiate from vegetative cells at regular intervals along each filament. The developmental process is initiated by an increase in the ratio of reduced carbon to reduced nitrogen. This cue triggers protein NtcA to activate transcription of nrrA, which leads to transcription of the hetR gene. HetR is a master transcription factor required for expression of many heterocyst-specific genes. One such gene is hetP, shown by Higa and Callahan in this edition of Molecular Microbiology to be able to replace hetR for most of the downstream events required for a functional heterocyst. Ectopic production of HetP in a hetR mutant allows the differentiation of heterocysts. These heterocysts can fix nitrogen under anaerobic conditions but they are unable to provide wild-type protection of nitrogenase from oxygen, so they cannot bypass all of the duties of HetR. Additionally, the 5Ј-flanking region of the hetP gene provides the best-characterized binding site for the HetR protein so far, a seven-base pair inverted repeat.
FEBS Letters, 2004
In the heterocystous cyanobacterium Anabaena PCC 7120, the modification state of the signalling PII protein is regulated according to the nitrogen regime of the cells, as already observed in some unicellular cyanobacteria. However, during the adaptation to diazotrophic growth conditions, PII is phosphorylated in vegetative cells while unphosphorylated in heterocysts. Isolation of mutants affected on PII modification state and analysis of their phenotypes allow us to show the implication of PII in the regulation of molecular nitrogen assimilation and more specifically, the requirement of unmodified state of PII in the formation of polar nodules of cyanophycin in heterocysts.
Journal of Bacteriology, 1996
Strain UCD 311 is a transposon-induced mutant of Nostoc sp. strain ATC C 29133 that is unable to fix nitrogen in air but does so under anoxic conditions and is able to establish a functional symbiotic association with the hornwort Anthoceros punctatus. These properties of strain UCD 311 are consistent with previous observations that protection against oxygen inactivation of nitrogenase is physiologically provided within A. punctatus tissue. Upon deprivation of combined nitrogen, strain UCD 311 clearly differentiates heterocysts and contains typical heterocyst-specific glycolipids; it also makes apparently normal akinetes upon phosphate starvation. Sequence analysis adjacent to the point of the transposon insertion revealed an open reading frame designated devR. Southern analysis established that similar sequences are present in other heterocyst-forming cyanobacteria. devR putatively encodes a protein of 135 amino acids with high similarity to the receiver domains of response regulat...
Molecular microbiology, 2015
Many filamentous cyanobacteria respond to the external cue of nitrogen scarcity by the differentiation of heterocysts, cells specialized in the fixation of atmospheric nitrogen in oxic environments. Heterocysts follow a spatial pattern along the filament of two heterocysts separated by ca. 10-15 vegetative cells performing oxygenic photosynthesis. HetR is a transcriptional regulator that directs heterocyst differentiation. In the model strain Anabaena sp. PCC 7120, the HetR protein was observed in various oligomeric forms in vivo, including a tetramer that peaked with maximal hetR expression during differentiation. Tetramers were not detected in a hetR point mutant incapable of differentiation, but were conspicuous in an over-differentiating strain lacking the PatS inhibitor. In differentiated filaments the HetR tetramer was restricted to heterocysts, being undetectable in vegetative cells. HetR co-purified with RNA polymerase from Anabaena mainly as a tetramer. In vitro, purified r...