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At least 721 records · Page 40Linked to original sources
PubMed2005

Dynamics of fluxes through photosynthetic complexes in response to changing light and inorganic carbon acclimation in Synechococcus elongatus.

Cyanobacteria acclimate to environmental inorganic carbon (C(i)) concentrations through re-organisations of photosynthetic function and the induction of carbon concentrating mechanisms (CCMs), which alter and constrain their subsequent acclimation to changing light. We grew cells acclimated to high C(i) (4 mM) or low C(i) (0.02 mM), shifted them from 50 micromol m(-2) s(-1) to 500 micromol m(-2) s(-1), and quantified their photosynthetic performance in parallel with quantitation of allocations to key indicator macromolecules. Pigments cell(-1) declined, PsbA (PS II), AtpB (ATP Synthase), RbcL (Rubisco) and GlnA (Glutamine Synthetase) increased, and PsaC (PS I) remained stable through the light shift. The increase in these protein pools was slower and smaller in low C(i) cells, but acted in both cell types to re-normalise the electron fluxes through the catalytic complexes back toward values before the light shift (for PsbA and GlnA) or even below the initial flux per complex (for RbcL). In contrast, an increased electron flux per PsaC was sustained for at least 6 h after the increase in light. Initially, high levels of PS II cell(-1) and PS II connectivity in high C(i) cells caused a more rapid net photoinactivation of PS II in high C(i) cells than in low C(i) cells, depressing the rate of PS II-specific electron transport (PS II ETR) to levels similar to linear ETR (net O(2) evolution minus respiration). In low C(i) cells, PS II ETR remained in excess of linear ETR and may have helped maintain CCM activity. The pool sizes of PsbA, AtpB and GlnA correlated with cellular growth rate, and changed at similar rates in high C(i) and low C(i) cells when expressed on a generational rather than chronological timescale, which has implications for differing ecology of high and low C(i) cells under variable natural light.

Acclimatization↗
PubMed2006

Structural and dynamic repercussions of heme binding and heme-protein cross-linking in Synechococcus sp. PCC 7002 hemoglobin.

The recombinant two-on-two hemoglobin from the cyanobacterium Synechoccocus sp. PCC 7002 (S7002 rHb) is a bishistidine hexacoordinate globin capable of forming a covalent cross-link between a heme vinyl and a histidine in the C-terminal helix (H helix). Of the two heme axial histidines, His46 (in the E helix, distal side) and His70 (in the F helix, proximal histidine), His46 is displaced by exogenous ligands. S7002 rHb can be readily prepared as an apoglobin (apo-rHb), a non-cross-linked hemichrome (ferric iron and histidine axial ligands, rHb-R), and a cross-linked hemichrome (rHb-A). To determine the effects of heme binding and subsequent cross-linking, apo-rHb, rHb-R, and rHb-A were subjected to thermal denaturation and 1H/2H exchange. Interpretation of the latter data was based on nuclear magnetic resonance assignments obtained with uniformly 15N- and 13C,15N-labeled proteins. Apo-rHb was found to contain a cooperative structural core, which was extended and stabilized by heme binding. Cross-linking resulted in further stabilization attributed mainly to an unfolded-state effect. Protection factors were higher at the cross-link site and near His70 in rHb-A than in rHb-R. In contrast, other regions became less resistant to exchange in rHb-A. These included portions of the B and E helices, which undergo large conformational changes upon exogenous ligand binding. Thus, the cross-link readjusted the dynamic properties of the heme pocket. 1H/2H exchange data also revealed that the B, G, and H helices formed a robust core regardless of the presence of the heme or cross-link. This motif likely encompasses the early folding nucleus of two-on-two globins.

Circular Dichroism↗
PubMed2005

NblC, a novel component required for pigment degradation during starvation in Synechococcus PCC 7942.

Adjustment of photosynthetic light harvesting to ambient conditions is essential to allow efficient energy capturing and to prevent surplus excitation and the cellular damage resulting from it. Degradation of the cyanobacterial light harvesting complex, the phycobilisome, is a general acclimation response occurring under various stress conditions. This study identifies a novel component, NblC, which mediates phycobilisome degradation under nitrogen, sulphur and phosphorus starvation. Our study indicates the requirement of NblC for efficient expression of nblA, an essential component of the degradation pathway; accumulation of nblA transcripts upon nutrient starvation was impaired in the NblC-mutant. Furthermore, expression of NblC under the control of a foreign promoter resulted in accumulation of nblA transcripts and degradation of the light harvesting complex. Transcription of nblC is induced upon nutrient starvation, suggesting the requirement of elevated levels of NblC under these conditions. Importantly, NblC could not exert its positive effect on nblA expression in the absence of the response regulator NblR. Sequence alignment suggests kinase motifs as well as homology of NblC to anti-sigma factors. Accordingly, we suggest a mode of action for this newly identified modulator, which provides new insights into regulation of gene expression in response to environmental stimuli.

Amino Acid Sequence↗
PubMed2006

Specific binding of D1 protein degradation products to the psbAI promoter in Synechococcus sp. strain PCC 7942.

The D1:1 protein and its potentially occurring degradation products were overexpressed in Escherichia coli. Protein-DNA interaction is shown for the promoter region of psbAI. The D1:1 degradation products may be involved in transcription regulation of psbAI by binding in the promoter region. Additionally, C-terminal fragments of the D1 protein bind to a sequence with similarity to isiB, a gene which encodes a flavodoxin-like protein.

Blotting, Western↗
PubMed2003

Computational inference of regulatory pathways in microbes: an application to phosphorus assimilation pathways in Synechococcus sp. WH8102.

We present a computational protocol for inference of regulatory and signaling pathways in a microbial cell, through literature search, mining "high-throughput'' biological data of various types, and computer-assisted human inference. This protocol consists of four key components: (a) construction of template pathways for microbial organisms related to the target genome, which either have been extensively studied and/or have a significant amount of (relevant) experimental data, (b) inference of initial pathway models for the target genome, through combining the template pathway models and target genome-specific information, (c) refinement and expansion of the initial pathway models through applications of various data mining tools, including phylogenetic profile analysis, inference of protein-protein interactions, and prediction of transcription factor binding sites, and (d) validation and refinement of the pathway models using pathway-specific experimental data or other information. To demonstrate the effectiveness of this procedure, we have applied it to the construction of the phosphorus assimilation pathways in cyanobacterium sp. WH8102. We present, in this paper, a model of the core components of this pathway.

Bacterial Proteins↗
PubMed2001

Structure of c-phycocyanin from the thermophilic cyanobacterium Synechococcus vulcanus at 2.5 A: structural implications for thermal stability in phycobilisome assembly.

The crystal structure of the light-harvesting phycobiliprotein, c-phycocyanin from the thermophilic cyanobacterium Synechochoccus vulcanus has been determined by molecular replacement to 2.5 A resolution. The crystal belongs to space group R32 with cell parameters a=b=188.43 A, c=61.28 A, alpha=beta=90 degrees, gamma=120 degrees, with one (alphabeta) monomer in the asymmetric unit. The structure has been refined to a crystallographic R factor of 20.2 % (R-free factor is 24.4 %), for all data to 2.5 A. The crystals were grown from phycocyanin (alphabeta)(3) trimers that form (alphabeta)(6) hexamers in the crystals, in a fashion similar to other phycocyanins. Comparison of the primary, tertiary and quaternary structures of the S. vulcanus phycocyanin structure with phycocyanins from both the mesophilic Fremyella diplsiphon and the thermophilic Mastigocladus laminosus were performed. We show that each level of assembly of oligomeric phycocyanin, which leads to the formation of the phycobilisome structure, can be stabilized in thermophilic organisms by amino acid residue substitutions. Each substitution can form additional ionic interactions at critical positions of each association interface. In addition, a significant shift in the position of ring D of the B155 phycocyanobilin cofactor in the S. vulcanus phycocyanin, enables the formation of important polar interactions at both the (alphabeta) monomer and (alphabeta)(6) hexamer association interfaces.

Algal Proteins↗