Mechanism In Cyanobacteria Research Articles

Modelling circadian rhythms of protein KaiA, KaiB and KaiC interactions in cyanobacteria

Cyanobacteria are the simplest organisms known that exhibit circadian rhythms. The mechanism of circadian rhythm generation in cyanobacteria is different from eukaryotes. Based on the recent experiments about the interaction of KaiA, KaiB, and KaiC proteins with the generation of circadian rhythms in vitro, we developed a mathematical model to describe post-translational oscillations and the possible chemical reactions involved in the circadian clock mechanism of cyanobacteria. In this model, a series of differential equations, with linear kinetics for binding of proteins, Michaelis – Menten kinetics for enzymatic processes and a term including an explicit delay for dissociation of the KaiA/KaiB/phospho-KaiC complex, are proposed describing the dynamics of the chemistry. It is demonstrated that the mathematical system can lead to circadian oscillation within a range of parameter values.

Proteomic studies of the thylakoid membrane ofSynechocystis sp. PCC 6803

Purified thylakoid membranes from the cyanobacterium Synechocystis sp. PCC 6803 were used for the first time in proteomic studies. The membranes were prepared by a combination of sucrose density centrifugation and aqueous polymer two-phase partitioning. In total, 76 different proteins were identified from 2- and 1-D gels by MALDI-TOF MS analysis. Twelve of the identified proteins have a predicted Sec/Tat signal peptide. Fourteen of the proteins were known, or predicted to be, integral membrane proteins. Among the proteins identified were subunits of the well-characterized thylakoid membrane constituents Photosystem I and II, ATP synthase, cytochrome b6f-complex, NADH dehydrogenase, and phycobilisome complex. In addition, novel thylakoid membrane proteins, both integral and peripheral were found, including enzymes involved in protein folding and pigment biosynthesis. The latter were the chlorophyll biosynthesis enzymes, light-dependent protochlorophyllide reductase and geranylgeranyl reductase as well as phytoene desaturase involved in carotenoid biosynthesis and a water-soluble carotenoid-binding protein. Interestingly, in view of the protein sorting mechanism in cyanobacteria, one of the two signal peptidases type I of Synechocystis was found in the thylakoid membrane, whereas the second one has been identified previously in the plasma membrane. Sixteen proteins are hypothetical proteins with unknown function.

Effects of salt stress on basic processes of photosynthesis

Salt stress causes decrease in plant growth and productivity by disrupting physiological processes, especially photosynthesis. The accumulation of intracellular sodium ions at salt stress changes the ratio of K : Na, which seems to affect the bioenergetic processes of photosynthesis. Both multiple inhibitory effects of salt stress on photosynthesis and possible salt stress tolerance mechanisms in cyanobacteria and plants are reviewed.

Low‐temperature modulation of the redox properties of the acceptor side of photosystem II: photoprotection through reaction centre quenching of excess energy

Although it has been well established that acclimation to low growth temperatures is strongly correlated with an increased proportion of reduced QA in all photosynthetic groups, the precise mechanism controlling the redox state of QA and its physiological significance in developing cold tolerance in photoautotrophs has not been fully elucidated. Our recent thermoluminescence (TL) measurements of the acceptor site of PSII have revealed that short‐term exposure of the cyanobacterium Synechococcus sp. PCC 7942 to cold stress, overwintering of Scots pine (Pinus sylvestris L.), and acclimation of Arabidopsis plants to low growth temperatures, all caused a substantial shift in the characteristic TM of S2QB– recombination to lower temperatures. These changes were accompanied by much lower overall TL emission, restricted electron transfer between QA and QB, and in Arabidopsis by a shift of the S2QA–‐related peak to higher temperatures. The shifts in recombination temperatures are indicative of a lower activation energy for the S2QB– redox pair and a higher activation energy for the S2QA– redox pair. This results in an increase in the free‐energy gap between P680+QA– and P680+Pheo– and a narrowing of the free energy gap between QA and QB electron acceptors. We propose that these effects result in an increased population of reduced QA (QA–), facilitating non‐radiative P680+QA– radical pair recombination within the PSII reaction centre. The proposed reaction centre quenching could be an important protective mechanism in cyanobacteria in which antenna and zeaxanthin cycle‐dependent quenching are not present. In herbaceous plants, the enhanced capacity for dissipation of excess light energy via PSII reaction centre quenching following cold acclimation may complement their capacity for increased utilization of absorbed light through CO2 assimilation and carbon metabolism. During overwintering of evergreens, when photosynthesis is inhibited, PSII reaction centre quenching may complement non‐photochemical quenching within the light‐harvesting antenna when zeaxanthin cycle‐dependent energy quenching is thermodynamically restricted by low temperatures. We suggest that PSII reaction centre quenching is a significant mechanism enabling cold‐acclimated organisms to acquire increased resistance to high light.

RNA Polyadenylation and Degradation in Cyanobacteria Are Similar to the Chloroplast but Different from Escherichia coli

The mechanism of RNA degradation in Escherichia coli involves endonucleolytic cleavage, polyadenylation of the cleavage product by poly(A) polymerase, and exonucleolytic degradation by the exoribonucleases, polynucleotide phosphorylase (PNPase) and RNase II. The poly(A) tails are homogenous, containing only adenosines in most of the growth conditions. In the chloroplast, however, the same enzyme, PNPase, polyadenylates and degrades the RNA molecule; there is no equivalent for the E. coli poly(A) polymerase enzyme. Because cyanobacteria is a prokaryote believed to be related to the evolutionary ancestor of the chloroplast, we asked whether the molecular mechanism of RNA polyadenylation in the Synechocystis PCC6803 cyanobacteria is similar to that in E. coli or the chloroplast. We found that RNA polyadenylation in Synechocystis is similar to that in the chloroplast but different from E. coli. No poly(A) polymerase enzyme exists, and polyadenylation is performed by PNPase, resulting in heterogeneous poly(A)-rich tails. These heterogeneous tails were found in the amino acid coding region, the 5' and 3' untranslated regions of mRNAs, as well as in rRNA and the single intron located at the tRNA(fmet). Furthermore, unlike E. coli, the inactivation of PNPase or RNase II genes caused lethality. Together, our results show that the RNA polyadenylation and degradation mechanisms in cyanobacteria and chloroplast are very similar to each other but different from E. coli.

Evolution and diversity of CO2 concentrating mechanisms in cyanobacteria.

Cyanobacteria have developed an effective photosynthetic CO2 concentrating mechanism (CCM) for improving the efficiency of carboxylation by a relatively inefficient Rubisco. The development of this CCM was presumably in response to the decline in atmospheric CO2 levels and rising O2, both of which were triggered by the development of oxygenic photosynthesis by cyanobacteria themselves. In the past few years there has been a rapid expansion in our understanding of the mechanism and genes responsible for the CCM. In addition, there has been a recent expansion in the availability of complete cyanobacterial genomes, thus increasing our potential to examine questions regarding both the evolution and diversity of components of the CCM across cyanobacteria. This paper considers various CCM and photosynthesis gene components across eight cyanobacteria where significant genomic information is available. Significant conclusions from our analysis of the distribution of various genes indicated the following. Firstly, cyanobacteria have developed with two types of carboxysomes, and this is correlated with the form of Rubisco present. We have coined the terms α-cyanobacteria to refer to cyanobacteria containing Form 1A Rubisco and α-carboxysomes, and β-cyanobacteria having Form 1B Rubisco and β-carboxysomes. Secondly, there are two NDH-1 CO2 uptake systems distributed variably, withProchlorococcus marinus species appearing to lack this CO2 uptake system. There are at least two HCO3- transport systems distributed variably, with some α-cyanobacteria having an absence of systems identified in β-cyanobacteria. Finally, there are multiple forms of carbonic anhydrases (CAs), but with only β-carboxysomal CA having a clearly shown role at present. The α-cyanobacteria appear to lack a clearly identifiable carboxysomal CA. A pathway for the evolution of cyanobacterial CCMs is proposed. The acquisition of carboxysomes triggered by the rapid decline of atmospheric CO2 in the Phanerozoic is argued to be the initial step. This would then be followed by the development of NDH-1 CO2-uptake systems, followed by the development of low-and high-affinity HCO3- transporters. An intriguing question is, were carboxysomes developed first in cyanobacteria, or did they originate by the lateral transfer of pre-existing proteobacterial bacterial microcompartment genes? The potentially late evolution of the CCM genes in cyanobacteria argues for a polyphyletic and separate evolution of CCMs in cyanobacteria, algae, and higher plants.

Analysis of PSI and PSII driven electron transportduring steady-state photosynthesis in the cyanobacteriumSynechococcus PCC7942

Photosynthetic electron transport is required for the transport of CO2 and HCO3- in Synechococcus PCC 7942. This transport supports the CO2 concentrating mechanism in cyanobacteria. The roles that linear and cyclic electron flow play in the energization of these processes is unclear. This study describes a system for measuring the quantum yields of photochemistry in both photosystems and, thus, the extent of electron flow, during steady-state cyanobacterial photosynthesis. These measurements were made in a custom-built cuvette coupled by a membrane inlet to a mass spectrometer enabling the concomitant measurement of photosynthetic gas exchange. In wild-type cells, the relationship between f PSI and f PSII was found to be linear between the CO2 compensation point and to approximately ¼ Vmax. The ratio of f PSI/f PSII was always greater than 1 and increased as net photosynthesis approached zero. This was suggestive of significant cyclic electron transport around PSI which became more pronounced as the rate of Ci supply decreased. Whether CO2 or HCO3- was used to drive photosynthesis the relationship between f PSI and f PSII was the same indicative of similar rates of linear and cyclic electron transport. Since we found no greater engagement of f PSI in the presence of enhanced CO2 supply we could not provide evidence for a model of CO2 transport coupled exclusively to cyclic electron transport. A double mutant (ndhD3-/ndhD4-) of Synechococcus PCC7942 in which CO2 transport is absent showed an alteration in electron transport properties relative to wild-type cells.

The inorganic carbon-concentrating mechanism in cyanobacteria: induction and ecological significance

In this minireview we focus on certain aspects of the induction, function, and ecophysiological significance of the inorganic carbon-concentrating mechanism in cyanobacteria. Since this entire issue is dedicated to various aspects of this mechanism, we mainly discuss some of the recent studies in our laboratory and point to open questions and perspectives.Key words: CO2, cyanobacteria, inorganic carbon-concentrating mechanism, photosynthesis.

Protein phosphorylation and its possible involvement in the induction of the high-affinity CO2 concentrating mechanism in cyanobacteria

Cyanobacteria as well as eukaryotic algae possess a CO2 concentrating mechanism that enables the cells to use low CO2 concentrations very efficiently for photosynthesis. The efficiency of the CO2 concentrating mechanism changes in response to environmental changes, especially the availability of inorganic carbon, but the underlying mechanisms that are involved in the regulation of the induction are unknown. This review deals with the occurrence of protein phosphorylation in cyanobacteria and highlights the possible involvement of post-translational modifications of existing proteins in the induction process, which leads to a high-affinity state of the CO2 concentrating mechanism.Key words: cyanobacteria, CO2 concentrating mechanism, protein kinase, protein phosphorylation, post-translational regulation.

The use of mutants in the analysis of the CO2-concentrating mechanism in cyanobacteria

Mutants of cyanobacteria defective in parts of the CO2-concentrating mechanism are classified into three types. (i) Mutants defective in inorganic carbon transporters. One of these mutants was constructed by inactivating cmpA encoding 42 kDa protein in the cytoplasmic membrane. (ii) Mutants defective in NAD(P)H dehydrogenase(s). There are five ndhD genes in Synechocystis PCC6803, two of them expressed constitutively and three inducible by low CO2. Two kinds of NAD(P)H dehydrogenase appear to be involved in energizing and inducing the high affinity inorganic carbon transport system. (iii) Mutants defective in carboxysome with impaired ccm or icfA genes. New type of mutants with impaired cotA (renamed as pxcA) have also been isolated. These mutants did not show light-induced proton extrusion and were unable to grow at acidic pHs. A mutant constructed by inactivating cotA (pxcA) in the wild-type Synechocystis was unable to transport CO2 at pH 6.5. We concluded that cotA (pxcA) has a role in light-induced proton extrusion that is essential at acidic pHs to extrude protons produced during CO2 transport.Key words: CO2-concentrating mechanism (CCM), CO2 transport, NAD(P)H dehydrogenase, proton extrusion, carboxysome, mutant.

Protein phosphorylation and its possible involvement in the induction of the high-affinity CO<sub>2</sub> concentrating mechanism in cyanobacteria

Protein phosphorylation and its possible involvement in the induction of the high-affinity CO<sub>2</sub> concentrating mechanism in cyanobacteria

The inorganic carbon-concentrating mechanism in cyanobacteria: induction and ecological significance

The inorganic carbon-concentrating mechanism in cyanobacteria: induction and ecological significance

The use of mutants in the analysis of the CO<sub>2</sub>-concentrating mechanism in cyanobacteria

The use of mutants in the analysis of the CO<sub>2</sub>-concentrating mechanism in cyanobacteria

Improved 5-step modeling of the Photosystem II S-state mechanism in cyanobacteria

We present a model of the S-state mechanism, as well as an improved eigenvalue analysis, that integrate into a coherent ensemble several features found since the S-state model was initially developed. These features include the presence of S-1, deactivations in the dark interval between flashes, and the change in the number of active PS II centers by photoinhibition or photoactivation. A new feature is the capacity to predict the steady-state distribution of S-states under conditions of steady photoinhibition or photoactivation. The improved eigenvalue analysis allowed the calculation of the initial S-state distribution. In addition, the model resolved 'true' photochemical misses from apparent misses due to deactivations in the dark interval between flashes. The model suggested that most of the misses that are commonly reported are due to deactivations, and not to an intrinsic inefficiency of the photochemical mechanism of PS II. Because models that allow double-hits encompassing the S2 to S3 transition often predict negative initial quantities of S2 in cyanobacteria, our proposed model specifically prohibited them. The model accounts for inhomogeneous misses and a steady-state distribution of the type (S2)≈(S1)>(S3)≈(S0). This 5-step model uses only 4 probabilities, and is therefore easy to handle. The use of this model is critical for the analysis of several cyanobacterial strains, as well as for any species that show non-negligible deactivations in the dark interval between flashes.

ラン藻のＣＯ２濃縮機構

ラン藻のＣＯ２濃縮機構

Isolation of a Putative Carboxysomal Carbonic Anhydrase Gene from the Cyanobacterium Synechococcus PCC7942

The Type II mutants of the cyanobacterium Synechococcus PCC7942 (G.D. Price, M.R. Badger [1989] Plant Physiol 91: 514-525) are able to accumulate a large pool of inorganic carbon inside the cell, but are unable to utilize it for CO(2) fixation, resulting in a high CO(2)-requiring phenotype. We have isolated a 3.5-kb BamHI clone (pT2) that complements the Type II mutants, and complementation analysis with DNA subclones indicated that the complementing region was located in the 0.75-kb XhoI-Bg/II fragment. This same region hybridized to the chloroplastic carbonic anhydrase (CA) gene from spinach on Southern blots and to a mRNA of approximate 1 kb on northern blots. Restriction mapping and sequence analysis revealed that pT2 is the same as a genomic clone (pBM3.8) that complements another high CO(2)-requiring (temperature sensitive) mutant, C3P-O (E. Suzuki, H. Fukuzawa, S. Miyachi [1991] Mol Gen Genet 226: 401-408). Recently, a 272-amino acid open reading frame showing 22% homology with pea and spinach chloroplast CA genes was identified in clone pBM3.8 (H. Fukuzawa, E. Suzuki, Y. Komukal, S. Miyachi [1992] Proc Natl Acad Sci USA 89: 4437-4441). CA activity was detected in Escherichia coli cells transformed with subclones of pT2 (pT2-A and pT2-A1) containing the HindIII-Bg/II fragment, and the expressed CA has properties similar to those of the CA activity associated with carboxysomes purified from Synechococcus PCC7942 (G.D. Price, J.R. Coleman, M.R. Badger [1992] Plant Physiol 100: 784-793). Therefore, it is reasonable to conclude that the HindIII-Bg/II fragment codes for the carboxysomal CA gene product. The result is discussed in the context of the role that carboxysomal CA plays in the operation of the CO(2)-concentrating mechanism in cyanobacteria.

Association of Carbonic Anhydrase Activity with Carboxysomes Isolated from the Cyanobacterium Synechococcus PCC7942

The development of a simple method for the isolation of purified carboxysomes from the cyanobacterium Synechococcus PCC7942 has made it possible to identify a specific and inducible, intracellular carbonic anhydrase (CA) activity that is strongly associated with carboxysomes. This was shown, in part, through enzyme recovery experiments that indicated that a clear majority of a CA activity that is sensitive to the CA inhibitor ethoxyzolamide (I(50) = 4 mum) copurifies with a majority of the cell's ribulose-1,5-bisphosphate carboxylase/oxygenase activity in a highly purified pelletable fraction. Electron microscopy of this pelletable fraction revealed the presence of carboxysomes that were physically intact. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of carboxysome proteins showed that the large and small subunits of ribulose-1,5-bisphosphate carbosylase/oxygenase were clearly prominent and that several other minor proteins could be distinguished. The specific location of this carboxysomal CA activity is further reinforced by the finding that a previously isolated high CO(2)-requiring mutant, Type II/No. 68 (G.D. Price, M.R. Badger [1989] Plant Physiol 91: 514-525), displayed a 30-fold reduction in carboxysome-associated CA activity when tested under optimal conditions. Carboxysomal CA has the unusual property of being inactivated by dithiothreitol. The enzyme also requires 20 mm Mg(2+) (as MgSO(4)) for near maximum activity; other divalent cations, such as Ca(2+) and Mn(2+), also stimulate carboxysomal CA activity, but to a lesser extent than Mg(2+). Results are discussed in relation to the role of carboxysomes in the CO(2)-concentrating mechanism in cyanobacteria and the role that carboxysomal CA activity appears to play in this process.

The CO2 concentrating mechanism in cyanobacteria and microalgae

Over the past 10 years it has become clear that cyanobacteria and microalgae possess mechanisms for actively acquiring inorganic carbon from the external medium and are able to use this to elevate the CO 2 concentration around the active site of the primary photosynthetic carboxylating enzyme, ribulose bisphosphate carboxylase-oxygenase (Rubisco)

Physiological and Molecular Aspects of the Inorganic Carbon-Concentrating Mechanism in Cyanobacteria

This paper reviews progress made in elucidating the inorganic carbon concentrating mechanism in cyanobacteria at the physiological and molecular levels. Emphasis is placed on the mechanism of inorganic carbon transport, physiological and genetical analysis of high-CO(2)-requiring mutants, the polypeptides induced during adaptation to low CO(2), the functional significance of carboxysomes, and the role of carbonic anhydrase. We also make occasional reference to the green algal inorganic carbon-concentrating mechanism.

The molecular and biochemical analyses of CO2‐concentrating mechanisms in cyanobacteria and microalgae

Abstract. The supply of dissolved inorganic carbon for photosynthesis in the aquatic environment is much more variable than that experienced by terrestrial plants. In response to this variability, cyanobacteria and many species of microalgae acclimate to rapid changes in the availability of dissolved inorganic carbon by the induction of high affinity/high capacity CO2‐concentrating systems (CCMs). Biochemical and molecular analyses of the acclimation response have recently identified several components that are required for efficient operation of the CCMs and CO2 assimilation. This has been accomplished using in vivo labelling studies, and characterization of high inorganic carbon (Ci) requiring cyanobacterial and algal mutants. The identification and regulation of expression of polypeptides synthesized in response to limiting Ci concentrations, and the proposed role of the carboxysome and the pyrenoid in the functioning of the CCMs are examined.