Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two endogenous plasmids are present in Synechococcus elongatus PCC 7942, a model organism for studying photosynthesis and circadian rhythms in cyanobacteria. The large plasmid, pANL, was shown previously to be involved in adaptation of S. elongatus cells to sulfur starvation, which provided the first evidence of cellular function of a cyanobacterial plasmid. Here, we report the complete sequence of pANL, which is 46,366 bp in length with 53% GC content and encodes 58 putative ORFs. The pANL plasmid can be divided into four structural and functional regions: the replication origin region, a signal transduction region, a plasmid maintenance region, and a sulfur-regulated region. Cosmid-based deletion analysis suggested that the plasmid maintenance and replication origin regions are required for persistence of pANL in the cells. Transposon-mediated mutagenesis and complementation-based pANL segregation assays confirmed that two predicted toxin-antitoxin cassettes encoded in the plasmid maintenance region, belonging to PemK and VapC families, respectively, are necessary for plasmid exclusion. The compact and efficient organization of sulfur-related genes on pANL may provide selective advantages in environments with limited sulfur.
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PMID:The complete sequence and functional analysis of pANL, the large plasmid of the unicellular freshwater cyanobacterium Synechococcus elongatus PCC 7942. 1835 36

The regulatory network for acclimation of the obligate photoautotrophic fresh water cyanobacterium Synechococcus elongatus PCC 7942 to iron (Fe) limitation was studied by transcript profiling with an oligonucleotide whole genome DNA microarray. Six regions on the chromosome with several Fe-regulated genes each were identified. The irpAB and fut region encode putative Fe uptake systems, the suf region participates in [Fe-sulfur] cluster assembly under oxidative stress and Fe limitation, the isiAB region encodes CP43' and flavodoxin, the idiCB region encodes the NuoE-like electron transport associated protein IdiC and the transcriptional activator IdiB, and the ackA/pgam region encodes an acetate kinase and a phosphoglycerate mutase. We also investigated the response of two S. elongatus PCC 7942 mutants to Fe starvation. These were mutant K10, lacking IdiB but containing IdiC, and mutant MuD, representing a idiC-merodiploid mutant with a strongly reduced amount of IdiC as well as IdiB. The absence of IdiB in mutant K10 or the strongly reduced amount of IdiB in mutant MuD allowed for the identification of additional members of the Fe-responsive IdiB regulon. Besides idiA and the irpAB operon somB(1), somA(2), ftr1, ackA, pgam, and nat also seem to be regulated by IdiB. In addition to the reduced amount of IdiB in MuD, the low concentration of IdiC may be responsible for a number of additional changes in the abundance of mainly photosynthesis-related transcripts as compared to the wild type and mutant K10. This fact may explain why it has been impossible to obtain a fully segregated IdiC-free mutant, whereas it was possible to obtain a fully segregated IdiB-free mutant.
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PMID:Transcript profiling reveals new insights into the acclimation of the mesophilic fresh-water cyanobacterium Synechococcus elongatus PCC 7942 to iron starvation. 1842 27

Excess light is harmful for photosynthetic organisms. The cyanobacterium Synechocystis PCC 6803 protects itself by dissipating the excess of energy absorbed by the phycobilisome, the water-soluble antenna of Photosystem II, into heat decreasing the excess energy arriving to the reaction centers. Energy dissipation results in a detectable decrease of fluorescence. The soluble Orange Carotenoid Protein (OCP) is essential for this blue-green light induced mechanism. OCP genes appear to be highly conserved among phycobilisome-containing cyanobacteria with few exceptions. Here, we show that only the strains containing a whole OCP gene can perform a blue-light induced photoprotective mechanism under both iron-replete and iron-starvation conditions. In contrast, strains containing only N-terminal and/or C-terminal OCP-like genes, or no OCP-like genes at all lack this light induced photoprotective mechanism and they were more sensitive to high-light illumination. These strains must adopt a different strategy to longer survive under stress conditions. Under iron starvation, the relative decrease of phycobiliproteins was larger in these strains than in the OCP-containing strains, avoiding the appearance of a population of dangerous, functionally disconnected phycobilisomes. The OCP-containing strains protect themselves from high light, notably under conditions inducing the appearance of disconnected phycobilisomes, using the energy dissipation OCP-phycobilisome mechanism.
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PMID:Occurrence and function of the orange carotenoid protein in photoprotective mechanisms in various cyanobacteria. 1869 21

The enormous macromolecular phycobilisome antenna complex (>4 MDa) in cyanobacteria and red algae undergoes controlled degradation during certain forms of nutrient starvation. The NblA protein (approximately 6 kDa) has been identified as an essential component in this process. We have used structural, biochemical, and genetic methods to obtain molecular details on the mode of action of the NblA protein. We have determined the three-dimensional structure of the NblA protein from both the thermophilic cyanobacterium Thermosynechococcus vulcanus and the mesophilic cyanobacterium Synechococcus elongatus sp. PCC 7942. The NblA monomer has a helix-loop-helix motif which dimerizes into an open, four-helical bundle, identical to the previously determined NblA structure from Anabaena. Previous studies indicated that mutations to NblA residues near the C terminus impaired its binding to phycobilisome proteins in vitro, whereas the only mutation known to affect NblA function in vivo is located near the protein N terminus. We performed random mutagenesis of the S. elongatus nblA gene which enabled the identification of four additional amino acids crucial for NblA function in vivo. This data shows that essential amino acids are not confined to the protein termini. We also show that expression of the Anabaena nblA gene complements phycobilisome degradation in an S. elongatus NblA-null mutant despite the low homology between NblAs of these cyanobacteria. We propose that the NblA interacts with the phycobilisome via "structural mimicry" due to similarity in structural motifs found in all phycobiliproteins. This suggestion leads to a new model for the mode of NblA action which involves the entire NblA protein.
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PMID:Structural, functional, and mutational analysis of the NblA protein provides insight into possible modes of interaction with the phycobilisome. 1871 7

Iron uptake in proteobacteria by TonB-dependent outer membrane transporters represents a well-explored subject. In contrast, the same process has been scarcely investigated in cyanobacteria. The heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120 is known to secrete the siderophore schizokinen, but its transport system has remained unidentified. Inspection of the genome of strain PCC 7120 shows that only one gene encoding a putative TonB-dependent iron transporter, namely alr0397, is positioned close to genes encoding enzymes involved in the biosynthesis of a hydroxamate siderophore. The expression of alr0397, which encodes an outer membrane protein, was elevated under iron-limited conditions. Inactivation of this gene caused a moderate phenotype of iron starvation in the mutant cells. The characterization of the mutant strain showed that Alr0397 is a TonB-dependent schizokinen transporter (SchT) of the outer membrane and that alr0397 expression and schizokinen production are regulated by the iron homeostasis of the cell.
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PMID:Alr0397 is an outer membrane transporter for the siderophore schizokinen in Anabaena sp. strain PCC 7120. 1880 87

Fur (ferric uptake regulator) is a prokaryotic transcriptional regulator that controls a large number of genes mainly related to iron metabolism. Several Fur homologues with different physiological roles are frequently found in the same organism. The genome of the filamentous cyanobacterium Anabaena (Nostoc) sp. PCC 7120 codes for three different fur genes. FurA is an essential protein involved in iron homoeostasis that also modulates dinitrogen fixation. FurA interacts with haem, impairing its DNA-binding ability. To explore functional differences between Fur homologues in Anabaena, factors affecting their regulation, as well as some biochemical characteristics, have been investigated. Although incubation of FurB with haem severely hinders its ability to interact with DNA, binding of haem to FurC could not be detected. Oxidative stress enhances the transcription of the three fur genes, especially that of furB and furC. In addition, overexpression of FurA and FurB in Escherichia coli increases survival when the cells are challenged with H(2)O(2) or Methyl Viologen (paraquat), a superoxide-anion-generating reagent. When present in saturating concentrations, FurB exhibits unspecific DNA-binding activity and protects DNA from cleavage produced by hydroxyl radicals or DNaseI. On the basis of these results, we suggest that, whereas at low concentrations FurB would act as a member of the Fur family, at saturating concentrations FurB protects DNA, showing a DNA-protection-during-starvation-like behaviour.
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PMID:New insights into the role of Fur proteins: FurB (All2473) from Anabaena protects DNA and increases cell survival under oxidative stress. 1894 13

The hetL gene from the cyanobacterium Nostoc sp. PCC 7120 encodes a 237 amino acid protein (25.6kDa) containing 40 predicted tandem pentapeptide repeats. Nostoc sp. PCC 7120 is a filamentous cyanobacterium that forms heterocysts, specialized cells capable of fixing atmospheric N(2) during nitrogen starvation in its aqueous environment. Under these conditions, heterocysts occur in a regular pattern of approximately one out of every 10-15 vegetative cells. Heterocyst differentiation is highly regulated involving hundreds of genes, one of which encodes PatS, thought to be an intercellular peptide signal made by developing heterocysts to inhibit heterocyst differentiation in neighboring vegetative cells, thus contributing to pattern formation and spacing of heterocysts along the filament. While overexpression of PatS suppresses heterocyst differentiation in Nostoc sp. PCC 7120, overexpression of HetL produces a multiple contiguous heterocyst phenotype with loss of the wild type heterocyst pattern, and strains containing extra copies of hetL allow heterocyst formation even in cells overexpressing PatS. Thus, HetL appears to interfere with heterocyst differentiation inhibition by PatS, however, the mechanism for HetL function remains unknown. As a first step towards exploring the mechanism for its biochemical function, the crystal structure of HetL has been solved at 2.0A resolution using sulfur anomalous scattering.
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PMID:The 2A resolution crystal structure of HetL, a pentapeptide repeat protein involved in regulation of heterocyst differentiation in the cyanobacterium Nostoc sp. strain PCC 7120. 1895 82

In the heterocyst-forming cyanobacterium Anabaena sp. PCC 7120 (also known as Nostoc sp. PCC 7120), it has been shown that spsB and susA, the genes coding for proteins related to sucrose synthesis and cleavage, respectively, exhibit converse expression regarding the nitrogen source. In the nitrogen-fixing filament, spsB expression is mostly localized to the heterocysts and susA is only expressed in vegetative cells. The aim of this work was to investigate the participation of NtcA, a global nitrogen regulator that operates in cyanobacteria, in the regulation of sucrose metabolism genes in Anabaena sp. PCC 7120. The induction of spsB expression observed in the filaments upon combined-nitrogen depletion was abolished in an NtcA-deficient mutant. In vitro experiments showed that NtcA binds specifically but with different affinities to two sites in the spsB promoter region. When susA expression was analyzed after a combined-nitrogen starvation, the levels of mRNA, polypeptide and activity increased in the mutant in comparison with the wild-type strain. Also, NtcA interacted with one site in the promoter region of susA. We conclude that sucrose metabolism is coordinated at the transcriptional level with nitrogen metabolism, suggesting a global metabolism regulating role for NtcA.
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PMID:Role of NtcA, a cyanobacterial global nitrogen regulator, in the regulation of sucrose metabolism gene expression in Anabaena sp. PCC 7120. 1908 79

A Ca2+ signal is required for the process of heterocyst differentiation in the filamentous diazotrophic cyanobacterium Anabaena sp. PCC 7120. This paper presents evidence that a transient increase in intracellular free Ca2+ is also involved in acclimation to nitrogen starvation in the unicellular non-diazotrophic cyanobacterium Synechococcus elongatus PCC 7942. The Ca2+ transient was triggered in response to nitrogen step-down or the addition of 2-oxoglutarate (2-OG), or its analogues 2,2-difluoropentanedioic acid (DFPA) and 2-methylenepentanedioic acid (2-MPA), to cells growing with combined nitrogen, suggesting that an increase in intracellular 2-OG levels precedes the Ca2+ transient. The signalling protein P(II) and the transcriptional regulator NtcA appear to be needed to trigger the signal. Suppression of the Ca2+ transient by the intracellular Ca2+ chelator N,N'-[1,2-ethanediylbis(oxy-2,1-phenylene)]bis[N-[2-[(acetyloxy)methoxy]-2-oxoethyl]]-,bis[(acetyloxy)methyl] ester (BAPTA-AM) inhibited expression of the glnB and glnN genes, which are involved in acclimation to nitrogen starvation and transcriptionally activated by NtcA. BAPTA-AM treatment partially inhibited expression of the nblA gene, which is involved in phycobiliprotein degradation following nutrient starvation and is regulated by NtcA and NblR; in close agreement, BAPTA-AM treatment partially inhibited bleaching following nitrogen starvation. Taken together, the results presented here strongly suggest an involvement of a defined Ca2+ transient in acclimation of S. elongatus to nitrogen starvation through NtcA-dependent regulation.
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PMID:Role of calcium in acclimation of the cyanobacterium Synechococcus elongatus PCC 7942 to nitrogen starvation. 1911 43

Filamentous cyanobacteria like Anabaena sp. PCC 7120 are able to develop a specialized cell type named heterocyst from vegetative cells in times of nitrogen starvation. Heterocyst development is controlled by the function of two master-regulators, NtcA and HetR. This review focuses on the remodeling of the cell wall during transition from the vegetative cell to a heterocyst, including the formation of the heterocyst-specific glycolipid layer and the heterocyst envelope polysaccharide layer. The functional assignment of genes involved therein, their genomic organization and their regulation are highlighted. Communication pathways and exchange routes for metabolites between heterocysts and vegetative cells are discussed. Further on, an overview of the heterocyst outer membrane proteome is given, together with possible functions of the identified proteins in the metabolism of heterocysts.
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PMID:The cell wall in heterocyst formation by Anabaena sp. PCC 7120. 1925 32


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