Elucidating the role of primary and secondary sphere Zn ligands in the cyanobacterial CO uptake complex NDH-1: The essentiality of arginine in zinc coordination and catalysis.

Inorganic carbon uptake in cyanobacteria is facilitated by an energetically intensive CO-concentrating mechanism (CCM). Specialized Type-1 NDH complexes function as a part of this mechanism to couple photosynthetic energy generated by redox reactions of the electron transport chain (ETC) to CO hydration. This active site of CO hydration incorporates an arginine side chain as a Zn ligand, diverging from the typical histidine and/or cysteine residues found in standard CAs.

Cyanobacterial Bioenergetics in Relation to Cellular Growth and Productivity.

Cyanobacteria, the evolutionary originators of oxygenic photosynthesis, have the capability to convert CO, water, and minerals into biomass using solar energy. This process is driven by intricate bioenergetic mechanisms that consist of interconnected photosynthetic and respiratory electron transport chains coupled. Over the last few decades, advances in physiochemical analysis, molecular genetics, and structural analysis have enabled us to gain a more comprehensive understanding of cyanobacterial bioenergetics.

Cyclic Electron Flow-Coupled Proton Pumping in sp. PCC6803 Is Dependent upon NADPH Oxidation by the Soluble Isoform of Ferredoxin:NADP-Oxidoreductase.

Ferredoxin:NADP-oxidoreductase (FNR) catalyzes the reversible exchange of electrons between ferredoxin (Fd) and NADP(H). Reduction of NADP by Fd via FNR is essential in the terminal steps of photosynthetic electron transfer, as light-activated electron flow produces NADPH for CO assimilation. FNR also catalyzes the reverse reaction in photosynthetic organisms, transferring electrons from NADPH to Fd, which is important in cyanobacteria for respiration and cyclic electron flow (CEF).

From manganese oxidation to water oxidation: assembly and evolution of the water-splitting complex in photosystem II.

The manganese cluster of photosystem II has been the focus of intense research aiming to understand the mechanism of HO-oxidation. Great effort has also been applied to investigating its oxidative photoassembly process, termed photoactivation that involves the light-driven incorporation of metal ions into the active MnCaO cluster. The knowledge gained on these topics has fundamental scientific significance, but may also provide the blueprints for the development of biomimetic devices capable of splitting water for solar energy applications.

Bioenergetics: To the dark side and back with cyanobacterial ATP synthase.

FF ATP synthases are remarkable because of their strict reversibility and the diverse mechanisms that prevent back reactions and futile cycling. Cyanobacteria power both the photosynthetic and respiratory electron transport chains in the same membrane system using a novel regulatory polypeptide that is expressed only at night.

Resolving the Rules of Robustness and Resilience in Biology Across Scales.

Why do some biological systems and communities persist while others fail? Robustness, a system's stability, and resilience, the ability to return to a stable state, are key concepts that span multiple disciplines within and outside the biological sciences. Discovering and applying common rules that govern the robustness and resilience of biological systems is a critical step toward creating solutions for species survival in the face of climate change, as well as the for the ever-increasing need for food, health, and energy for human populations. We propose that network theory provides a framework for universal scalable mathematical models to describe robustness and resilience and the relationship between them, and hypothesize that resilience at lower organization levels contribute to robust systems.

Electron flow through NDH-1 complexes is the major driver of cyclic electron flow-dependent proton pumping in cyanobacteria.

Cyclic electron flow (CEF) around photosystem I is vital to balancing the photosynthetic energy budget of cyanobacteria and other photosynthetic organisms. The coupling of CEF to proton pumping has long been hypothesized to occur, providing proton motive force (PMF) for the synthesis of ATP with no net cost to [NADPH]. This is thought to occur largely through the activity of NDH-1 complexes, of which cyanobacteria have four with different activities.

Light-driven formation of manganese oxide by today's photosystem II supports evolutionarily ancient manganese-oxidizing photosynthesis.

Water oxidation and concomitant dioxygen formation by the manganese-calcium cluster of oxygenic photosynthesis has shaped the biosphere, atmosphere, and geosphere. It has been hypothesized that at an early stage of evolution, before photosynthetic water oxidation became prominent, light-driven formation of manganese oxides from dissolved Mn(2+) ions may have played a key role in bioenergetics and possibly facilitated early geological manganese deposits. Here we report the biochemical evidence for the ability of photosystems to form extended manganese oxide particles.

The role of Ca and protein scaffolding in the formation of nature's water oxidizing complex.

Photosynthetic O evolution is catalyzed by the MnCaO cluster of the water oxidation complex of the photosystem II (PSII) complex. The photooxidative self-assembly of the MnCaO cluster, termed photoactivation, utilizes the same highly oxidizing species that drive the water oxidation in order to drive the incorporation of Mn into the high-valence MnCaO cluster. This multistep process proceeds with low quantum efficiency, involves a molecular rearrangement between light-activated steps, and is prone to photoinactivation and misassembly.

The D1-V185N mutation alters substrate water exchange by stabilizing alternative structures of the MnCa-cluster in photosystem II.

In photosynthesis, the oxygen-evolving complex (OEC) of the pigment-protein complex photosystem II (PSII) orchestrates the oxidation of water. Introduction of the V185N mutation into the D1 protein was previously reported to drastically slow O-release and strongly perturb the water network surrounding the MnCa cluster. Employing time-resolved membrane inlet mass spectrometry, we measured here the HO/HO-exchange kinetics of the fast (W) and slow (W) exchanging substrate waters bound in the S, S and S states to the MnCa cluster of PSII core complexes isolated from wild type and D1-V185N strains of Synechocystis sp.

Carbon/Nitrogen Metabolic Balance: Lessons from Cyanobacteria.

Carbon and nitrogen are the two most abundant nutrient elements for all living organisms, and their metabolism is tightly coupled. What are the signaling mechanisms that cells use to sense and control the carbon/nitrogen (C/N) metabolic balance following environmental changes? Based on studies in cyanobacteria, it was found that 2-phosphoglycolate derived from the oxygenase activity of Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) and 2-oxoglutarate from the Krebs cycle act as the carbon- and nitrogen-starvation signals, respectively, and their concentration ratio likely reflects the status of the C/N metabolic balance. We will present and discuss the regulatory principles underlying the signaling mechanisms, which are likely to be conserved in other photosynthetic organisms.

Synthetic DNA system for structure-function studies of the high affinity CO uptake NDH-1 protein complex in cyanobacteria.

The CO-concentrating mechanism (CCM) in cyanobacteria supports high rates of photosynthesis by greatly increasing the concentration of CO around the major carbon fixing enzyme, Rubisco. However, the CCM remains poorly understood, especially in regards to the enigmatic CO-hydration enzymes which couple photosynthetically generated redox energy to the hydration of CO to bicarbonate. This CO-hydration reaction is catalysed by specialized forms of NDH-1 thylakoid membrane complexes that contain phylogenetically unique extrinsic proteins that appear to couple CO hydration to NDH-1 proton pumping.

Impact of D1-V185 on the Water Molecules That Facilitate O Formation by the Catalytic MnCaO Cluster in Photosystem II.

The oxidations of the O-evolving MnCaO cluster in Photosystem II are coupled to the release of protons to the thylakoid lumen via one or more proton egress pathways. These pathways are comprised of extensive networks of hydrogen-bonded water molecules and amino acid side chains. The hydrophobic residue, D1-V185, is adjacent to numerous water molecules in one of these pathways.

Glycogen Synthesis and Metabolite Overflow Contribute to Energy Balancing in Cyanobacteria.

Understanding how living cells manage high-energy metabolites such as ATP and NADPH is essential for understanding energy transformations in the biosphere. Using light as the energy input, we find that energy charge (ratio of ATP over ADP+ATP) in the cyanobacterium Synechocystis sp. PCC 6803 varies in different growth stages, with a peak upon entry into the rapid growth phase, as well as a positive correlation with light intensity.

CO capture using limestone for cultivation of the freshwater microalga Chlorella sorokiniana PAZ and the cyanobacterium Arthrospira sp. VSJ.

The present study reports a process wherein CO is captured in the form of bicarbonates using calcium oxide and photosynthetically fixed into biomass. Microalgal cultures viz. Chlorella sorokiniana PAZ and Arthrospira sp.

Photoactivation: The Light-Driven Assembly of the Water Oxidation Complex of Photosystem II.

Photosynthetic water oxidation is catalyzed by the Mn4CaO5 cluster of photosystem II. The assembly of the Mn4O5Ca requires light and involves a sequential process called photoactivation. This process harnesses the charge-separation of the photochemical reaction center and the coordination environment provided by the amino acid side chains of the protein to oxidize and organize the incoming manganese ions to form the oxo-bridged metal cluster capable of H2O-oxidation.

Structural rearrangements preceding dioxygen formation by the water oxidation complex of photosystem II.

Photosynthetic water oxidation is catalyzed by the Mn4CaO5 cluster of photosystem II. Recent studies implicate an oxo bridge atom, O5, of the Mn4CaO5 cluster, as the "slowly exchanging" substrate water molecule. The D1-V185N mutant is in close vicinity of O5 and known to extend the lag phase and retard the O2 release phase (slow phase) in this critical last [Formula: see text] transition of water oxidation.

Systems and photosystems: cellular limits of autotrophic productivity in cyanobacteria.

Recent advances in the modeling of microbial growth and metabolism have shown that growth rate critically depends upon the optimal allocation of finite proteomic resources among different cellular functions and that modeling growth rates becomes more realistic with the explicit accounting for the costs of macromolecular synthesis, most importantly, protein expression. The "proteomic constraint" is considered together with its application to understanding photosynthetic microbial growth. The central hypothesis is that physical limits of cellular space (and corresponding solvation capacity) in conjunction with cell surface-to-volume ratios represent the underlying constraints on the maximal rate of autotrophic microbial growth.

Regulation of CO2 Concentrating Mechanism in Cyanobacteria.

In this chapter, we mainly focus on the acclimation of cyanobacteria to the changing ambient CO2 and discuss mechanisms of inorganic carbon (Ci) uptake, photorespiration, and the regulation among the metabolic fluxes involved in photoautotrophic, photomixotrophic and heterotrophic growth. The structural components for several of the transport and uptake mechanisms are described and the progress towards elucidating their regulation is discussed in the context of studies, which have documented metabolomic changes in response to changes in Ci availability. Genes for several of the transport and uptake mechanisms are regulated by transcriptional regulators that are in the LysR-transcriptional regulator family and are known to act in concert with small molecule effectors, which appear to be well-known metabolites.

Redox changes accompanying inorganic carbon limitation in Synechocystis sp. PCC 6803.

Inorganic carbon (Ci) is the major sink for photosynthetic reductant in organisms capable of oxygenic photosynthesis. In the absence of abundant Ci, the cyanobacterium Synechocystis sp. strain PCC6803 expresses a high affinity Ci acquisition system, the CO2-concentrating mechanisms (CCM), controlled by the transcriptional regulator CcmR and the metabolites NADP+ and α-ketoglutarate, which act as co-repressors of CcmR by modulating its DNA binding.

Parallel expression of alternate forms of psbA2 gene provides evidence for the existence of a targeted D1 repair mechanism in Synechocystis sp. PCC 6803.

The D1 protein of Photosystem II (PSII) is recognized as the main target of photoinhibitory damage and exhibits a high turnover rate due to its degradation and replacement during the PSII repair cycle. Damaged D1 is replaced by newly synthesized D1 and, although reasonable, there is no direct evidence for selective replacement of damaged D1. Instead, it remains possible that increased turnover of D1 subunits occurs in a non-selective manner due for example, to a general up-regulation of proteolytic activity triggered during damaging environmental conditions, such as high light.