Biochemical elucidation of citrate accumulation in Synechocystis sp. PCC 6803 via kinetic analysis of aconitase.
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ABSTRACT:
SUBMITTER: Nishii M
PROVIDER: S-EPMC8385029 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Synechocystis sp. PCC 6803 is a widely used model cyanobacterium whose genome has been well annotated. However, several additional small protein coding sequences (sORFs) have been recently identified, which might play important roles, for example in the regulation of cellular metabolism. Here, we analyzed the function of a sORF encoding a 44 amino acid peptide showing high similarity to the N-terminal part of aconitase (AcnB). The expression of the gene, which probably originated from a partial gene duplication of chromosomal acnB into the plasmid pSYSA, was verified and it was designated as acnSP. The protein-coding part of acnSP was inactivated by interposon mutagenesis. The obtained mutant displayed slower growth under photoautotrophic conditions with light exceeding 100 μmol photons m-2 s-1 and showed significant changes in the metabolome compared to wild type, including alterations in many metabolites associated to the tricarboxylic acid (TCA) cycle. To analyze a possible direct impact of AcnSP on aconitase, the recombinant Synechocystis enzyme was generated and biochemically characterized. Biochemical analysis revealed that addition of equimolar amounts of AcnSP resulted in an improved substrate affinity (lower K m) and lowered V max of aconitase. These results imply that AcnSP can regulate aconitase activity, thereby impacting the carbon flow into the oxidative branch of the cyanobacterial TCA cycle, which is mainly responsible for the synthesis of carbon skeletons needed for ammonia assimilation.
| S-EPMC7336809 | biostudies-literature
Project description:In recent years, there has been an increased interest in the research and development of sustainable alternatives to fossil fuels. Using photosynthetic microorganisms to produce such alternatives is advantageous, since they can achieve direct conversion of carbon dioxide from the atmosphere into the desired product, using sunlight as the energy source. Squalene is a naturally occurring 30-carbon isoprenoid, which has commercial use in cosmetics and in vaccines. If it could be produced sustainably on a large scale, it could also be used instead of petroleum as a raw material for fuels and as feedstock for the chemical industry. The unicellular cyanobacterium Synechocystis PCC 6803 possesses a gene, slr2089, predicted to encode squalene hopene cyclase (Shc), an enzyme converting squalene into hopene, the substrate for forming hopanoids. Through inactivation of slr2089 (shc), we explored the possibility to produce squalene using cyanobacteria. The inactivation led to accumulation of squalene, to a level over 70 times higher than in wild type cells, reaching 0.67 mg OD750(-1) L(-1). We did not observe any significant growth deficiency in the Δshc strain compared to the wild type Synechocystis, even at high light conditions, suggesting that the observed squalene accumulation was not detrimental to growth, and that formation of hopene by Shc is not crucial for growth under normal conditions, nor for high-light stress tolerance. Effects of different light intensities and growth stages on squalene accumulation in the Δshc strain were investigated. We also identified a gene, sll0513, as a putative squalene synthase in Synechocystis, and verified its function by inactivation. In this work, we show that it is possible to use the cyanobacterium Synechocystis to generate squalene, a hydrocarbon of commercial interest and a potential biofuel. We also report the first identification of a squalene hopene cyclase, and the second identification of squalene synthase, in cyanobacteria.
| S-EPMC3953072 | biostudies-literature
Project description:The effect of phycobilisome antenna-truncation in the cyanobacterium Synechocystis sp. PCC 6803 on biomass production and glycogen accumulation have not yet been fully clarified. To investigate these effects here, the apcE gene, which encodes the anchor protein linking the phycobilisome to the thylakoid membrane, was deleted in a glucose tolerant strain of Synechocystis sp. PCC 6803. Biomass production of the apcE-deleted strain under photoautotrophic and atmospheric air conditions was 1.6 times higher than that of strain PCC 6803 (1.32?±?0.01 versus 0.84?±?0.07 g cell-dry weight L(-1), respectively) after 15 days of cultivation. In addition, the glycogen content of the apcE-deleted strain (24.2?±?0.7%) was also higher than that of strain PCC 6803 (11.1?±?0.3%). Together, these results demonstrate that antenna truncation by deleting the apcE gene was effective for increasing biomass production and glycogen accumulation under photoautotrophic and atmospheric air conditions in Synechocystis sp. PCC 6803.
| S-EPMC4052703 | biostudies-literature
Project description:Heme is a cofactor for proteins participating in many important cellular processes, including respiration, oxygen metabolism and oxygen binding. The key enzyme in the heme biosynthesis pathway is ferrochelatase (protohaem ferrolyase, EC 4.99.1.1), which catalyzes the insertion of ferrous iron into protoporphyrin IX. In higher plants, the ferrochelatase enzyme is localized not only in mitochondria, but also in chloroplasts. The plastidic type II ferrochelatase contains a C-terminal chlorophyll a/b (CAB) motif, a conserved hydrophobic stretch homologous to the CAB domain of plant light harvesting proteins and light-harvesting like proteins. This type II ferrochelatase, found in all photosynthetic organisms, is presumed to have evolved from the cyanobacterial ferrochelatase. Here we describe a detailed enzymological study on recombinant, refolded and functionally active type II ferrochelatase (FeCh) from the cyanobacterium Synechocystis sp. PCC 6803. A protocol was developed for the functional refolding and purification of the recombinant enzyme from inclusion bodies, without truncation products or soluble aggregates. The refolded FeCh is active in its monomeric form, however, addition of an N-terminal His(6)-tag has significant effects on its enzyme kinetics. Strikingly, removal of the C-terminal CAB-domain led to a greatly increased turnover number, k(cat), compared to the full length protein. While pigments isolated from photosynthetic membranes decrease the activity of FeCh, direct pigment binding to the CAB domain of FeCh was not evident.
| S-EPMC3563542 | biostudies-literature
Project description:We designed and constructed a controllable inducing lysis system in Synechocystis sp. PCC 6803 to facilitate extracting lipids for biofuel production. Several bacteriophage-derived lysis genes were integrated into the genome and placed downstream of a nickel-inducible signal transduction system. We applied 3 strategies: (i) directly using the phage lysis cassette, (ii) constitutively expressing endolysin genes while restricting holin genes, and (iii) combining lysis genes from different phages. Significant autolysis was induced in the Synechocystis sp. PCC 6803 cells with this system by the addition of NiSO(4). Our inducible cyanobacterial lysing system eliminates the need for mechanical or chemical cell breakage and could facilitate recovery of biofuel from cyanobacteria.
| S-EPMC2799798 | biostudies-literature
Project description:BackgroundMetabolic engineering and synthetic biology of cyanobacteria offer a promising sustainable alternative approach for fossil-based ethylene production, by using sunlight via oxygenic photosynthesis, to convert carbon dioxide directly into ethylene. Towards this, both well-studied cyanobacteria, i.e., Synechocystis sp PCC 6803 and Synechococcus elongatus PCC 7942, have been engineered to produce ethylene by introducing the ethylene-forming enzyme (Efe) from Pseudomonas syringae pv. phaseolicola PK2 (the Kudzu strain), which catalyzes the conversion of the ubiquitous tricarboxylic acid cycle intermediate 2-oxoglutarate into ethylene.ResultsThis study focuses on Synechocystis sp PCC 6803 and shows stable ethylene production through the integration of a codon-optimized version of the efe gene under control of the Ptrc promoter and the core Shine-Dalgarno sequence (5'-AGGAGG-3') as the ribosome-binding site (RBS), at the slr0168 neutral site. We have increased ethylene production twofold by RBS screening and further investigated improving ethylene production from a single gene copy of efe, using multiple tandem promoters and by putting our best construct on an RSF1010-based broad-host-self-replicating plasmid, which has a higher copy number than the genome. Moreover, to raise the intracellular amounts of the key Efe substrate, 2-oxoglutarate, from which ethylene is formed, we constructed a glycogen-synthesis knockout mutant (ΔglgC) and introduced the ethylene biosynthetic pathway in it. Under nitrogen limiting conditions, the glycogen knockout strain has increased intracellular 2-oxoglutarate levels; however, surprisingly, ethylene production was lower in this strain than in the wild-type background.ConclusionMaking use of different RBS sequences, production of ethylene ranging over a 20-fold difference has been achieved. However, a further increase of production through multiple tandem promoters and a broad-host plasmid was not achieved speculating that the transcription strength and the gene copy number are not the limiting factors in our system.
| S-EPMC5324202 | biostudies-literature
Project description:BACKGROUND:There are an increasing number of studies regarding genetic manipulation of cyanobacteria to produce commercially interesting compounds. The majority of these works study the expression and optimization of a selected heterologous pathway, largely ignoring the wholeness and complexity of cellular metabolism. Regulation and response mechanisms are largely unknown, and even the metabolic pathways themselves are not fully elucidated. This poses a clear limitation in exploiting the rich biosynthetic potential of cyanobacteria. RESULTS:In this work, we focused on the production of two different compounds, the cyanogenic glucoside dhurrin and the diterpenoid 13R-manoyl oxide in Synechocystis PCC 6803. We used genome-scale metabolic modelling to study fluxes in individual reactions and pathways, and we determined the concentrations of key metabolites, such as amino acids, carotenoids, and chlorophylls. This allowed us to identify metabolic crosstalk between the native and the introduced metabolic pathways. Most results and simulations highlight the metabolic robustness of cyanobacteria, suggesting that the host organism tends to keep metabolic fluxes and metabolite concentrations steady, counteracting the effects of the heterologous pathway. However, the amino acid concentrations of the dhurrin-producing strain show an unexpected profile, where the perturbation levels were high in seemingly unrelated metabolites. CONCLUSIONS:There is a wealth of information that can be derived by combining targeted metabolite identification and computer modelling as a frame of understanding. Here we present an example of how strain engineering approaches can be coupled to 'traditional' metabolic engineering with systems biology, resulting in novel and more efficient manipulation strategies.
| S-EPMC5556357 | biostudies-literature
Project description:The biosynthesis pathway of carotenoids in cyanobacteria is partly described. However, the subcellular localization of individual steps is so far unknown. Carotenoid analysis of different membrane subfractions in Synechocystis sp. PCC6803 shows that "light" plasma membranes have a high carotenoid/protein ratio, when compared to "heavier" plasma membranes or thylakoids. The localization of CrtQ and CrtO, two well-defined carotenoid synthesis pathway enzymes in Synechocystis, was studied by epitope tagging and western blots. Both enzymes are locally more abundant in plasma membranes than in thylakoids, implying that the plasma membrane has higher synthesis rates of ?-carotene precursor molecules and echinenone.
| S-EPMC4470828 | biostudies-literature
Project description:Cyanobacteria require efficient protein-quality-control mechanisms to survive under dynamic, often stressful, environmental conditions. It was reported that three serine proteases, HtrA (high temperature requirement A), HhoA (HtrA homologue A) and HhoB (HtrA homologue B), are important for survival of Synechocystis sp. PCC 6803 under high light and temperature stresses and might have redundant physiological functions. In the present paper, we show that all three proteases can degrade unfolded model substrates, but differ with respect to cleavage sites, temperature and pH optima. For recombinant HhoA, and to a lesser extent for HtrA, we observed an interesting shift in the pH optimum from slightly acidic to alkaline in the presence of Mg2+ and Ca2+ ions. All three proteases formed different homo-oligomeric complexes with and without substrate, implying mechanistic differences in comparison with each other and with the well-studied Escherichia coli orthologues DegP (degradation of periplasmic proteins P) and DegS. Deletion of the PDZ domain decreased, but did not abolish, the proteolytic activity of all three proteases, and prevented substrate-induced formation of complexes higher than trimers by HtrA and HhoA. In summary, biochemical characterization of HtrA, HhoA and HhoB lays the foundation for a better understanding of their overlapping, but not completely redundant, stress-resistance functions in Synechocystis sp. PCC 6803.
| S-EPMC3195437 | biostudies-literature
Project description:Nitrogen is often a limiting nutrient in natural habitats. Therefore, cyanobacteria have developed multiple responses, which are controlled by transcription factor NtcA and the PII-signaling protein, to adapt to nitrogen deficiency. Transcriptional analyses of Synechocystis sp. strain PCC 6803 under nitrogen-deficient conditions revealed a highly induced gene (sll0783) which is annotated as encoding a conserved protein with an unknown function. This gene is part of a cluster of seven genes and has potential NtcA-binding sites in the upstream region. Homologues of this cluster occur in some unicellular, nondiazotrophic cyanobacteria and in several Alpha, Beta-, and Gammaproteobacteria, as well as in some Gram-positive bacteria. Most of the heterotrophic bacteria harboring this gene cluster are able to fix nitrogen and to produce polyhydroxybutyrate (PHB), whereas of the cyanobacteria, only Synechocystis sp. strain PCC 6803 can accumulate PHB. In this work, a Synechocystis sp. strain PCC 6803 sll0783 gene knockout mutant is characterized. This mutant is unable to accumulate PHB, a carbon and energy storage compound. In contrast, the levels of the carbon storage compound glycogen and the PHB precursor acetyl coenzyme A were similar to those of the wild type, indicating that the PHB-deficient phenotype does not likely result from a global deficiency in carbon metabolism. A specific deficiency in PHB synthesis was implied by the fact that the mutant exhibits impaired PHB synthase activity during prolonged nitrogen starvation. However, the expression of PHB synthase-encoding genes was not strongly affected in the mutant, suggesting that the impaired PHB synthase activity observed depends on a posttranscriptional process in which the product of sll0783 is involved.
| S-EPMC2937498 | biostudies-literature