Research Interests: Biophysics, Kinetics, Photochemistry, Photosynthesis, Fluorescence, and 15 moreBiology, Cyanobacteria, Membrane Proteins, Medicine, Biological Sciences, Mutation, Chlorophyll, Absorption spectroscopy, Light, photosystem I, Oxygen, Energy Transfer, Light Harvesting, Biochemistry and cell biology, and Dcmu
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A Synechococcus sp. strain PCC 7002 ΔpsaAB::cat mutant has been constructed by deletional interposon mutagenesis of the psaA and psaB genes through selection and segregation under low-light conditions. This strain can grow... more
A Synechococcus sp. strain PCC 7002 ΔpsaAB::cat mutant has been constructed by deletional interposon mutagenesis of the psaA and psaB genes through selection and segregation under low-light conditions. This strain can grow photoheterotrophically with glycerol as carbon source with a doubling time of 25 h at low light intensity (10 μE m(-2) s(-1)). No Photosystem I (PS I)-associated chlorophyll fluorescence emission peak was detected in the ΔpsaAB::cat mutant. The chlorophyll content of the ΔpsaAB::cat mutant was approximately 20% that of the wild-type strain on a per cell basis. In the absence of the PsaA and PsaB proteins, several other PS I proteins do not accumulate to normal levels. Assembly of the peripheral PS I proteins PsaC,PsaD, PsaE, and PsaL is dependent on the presence of the PsaA and PsaB heterodimer core. The precursor form of PsaF may be inserted into the thylakoid membrane but is not processed to its mature form in the absence of PsaA and PsaB. The absence of PS I reaction centers has no apparent effect on Photosystem II (PS II) assembly and activity. Although the mutant exhibited somewhat greater fluorescence emission from phycocyanin, most of the light energy absorbed by phycobilisomes was efficiently transferred to the PS II reaction centers in the absence of the PS I. No light state transition could be detected in the ΔpsaAB::cat strain; in the absence of PS I, cells remain in state 1. Development of this relatively light-tolerant strain lacking PS I provides an important new tool for the genetic manipulation of PS I and further demonstrates the utility of Synechococcus sp. PCC 7002 for structural and functional analyses of the PS I reaction center.
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Summary Photosystem I (PSI) converts photons into electrons with a nearly 100% quantum efficiency. Its minimal energy requirement for photochemistry corresponds to a 700-nm photon, representing the well-known “red limit” of oxygenic... more
Summary Photosystem I (PSI) converts photons into electrons with a nearly 100% quantum efficiency. Its minimal energy requirement for photochemistry corresponds to a 700-nm photon, representing the well-known “red limit” of oxygenic photosynthesis. Recently, some cyanobacteria containing the red-shifted pigment chlorophyll f have been shown to harvest photons up to 800 nm. To investigate the mechanism responsible for converting such low-energy photons, we applied steady-state and time-resolved spectroscopies to the chlorophyll-f-containing PSI and chlorophyll-a-only PSI of various cyanobacterial strains. Chlorophyll-f-containing PSI displays a less optimal energetic connectivity between its pigments. Nonetheless, it consistently traps long-wavelength excitations with a surprisingly high efficiency, which can only be achieved by lowering the energy required for photochemistry, i.e., by “breaking the red limit”. We propose that charge separation occurs via a low-energy charge-transfer state to reconcile this finding with the available structural data excluding the involvement of chlorophyll f in photochemistry.
Research Interests: Biochemistry, Physics, Materials Chemistry, Photochemistry, Photosynthesis, and 13 moreSpectroscopy, Environmental Chemistry, Chlorophyll, Chlorophyll Fluorescence, Medical Biochemistry, photosystem I, Photon, Photosystem II, Light Harvesting, Excitation Energy Transfer, Chlorophyll a, Chem, and Photoacclimation
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Research Interests: Photosynthesis, Biology, Near Infrared, Medicine, Biological Sciences, and 12 moreOrganelles, Protein Structure and Function, Mutagenesis, Bacteriochlorophyll, Bacteria, Genetic Recombination, Homologous Recombination, Energy Transfer, Light Harvesting, Green Sulfur Bacteria, Doubling Time, and Medical and Health Sciences
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Synechococcus sp. strain PCC 7002 is a robust, genetically tractable cyanobacterium that produces six different xanthophyll carotenoids (zeaxanthin, cryptoxanthin, myxoxanthophyll... more
Synechococcus sp. strain PCC 7002 is a robust, genetically tractable cyanobacterium that produces six different xanthophyll carotenoids (zeaxanthin, cryptoxanthin, myxoxanthophyll (myxol-2'-fucoside), echinenone,…
Research Interests: Biochemistry, Genetics, Photosynthesis, Biology, Oxidative Stress, and 15 moreMedicine, Mutation, Reactive Oxygen Species, Light, Nitrogen, photosystem I, Enzyme, Carotenoid, Synechococcus, Environmental Stress, Cell Proliferation, chlorophyll Content, Biochemistry and cell biology, Gene expression profiling, and high light
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The enzyme ferredoxin-NADP(+) oxidoreductase (FNR) from Synechococcus sp. PCC 7002 has an extended structure comprising three domains (FNR-3D) (Schluchter, W. M., and Bryant, D. A. (1992) Biochemistry 31, 3092-3102). Phycobilisome (PBS)... more
The enzyme ferredoxin-NADP(+) oxidoreductase (FNR) from Synechococcus sp. PCC 7002 has an extended structure comprising three domains (FNR-3D) (Schluchter, W. M., and Bryant, D. A. (1992) Biochemistry 31, 3092-3102). Phycobilisome (PBS) preparations from wild-type cells contained from 1.0 to 1.6 molecules of FNR-3D per PBS, with an average value of 1.3 FNR per PBS. A maximum of two FNR-3D molecules could be specifically bound to wild-type PBS via the N-terminal, CpcD-like domain of the enzyme when exogenous recombinant FNR-3D (rFNR-3D) was added. To localize the enzyme within the PBS, the interaction of PBS and their substructures with rFNR-3D was further investigated. The binding affinity of rFNR-3D for phycocyanin (PC) hexamers, which contained a 22-kDa proteolytic fragment derived from CpcG, the L(RC)(27) linker polypeptide, was higher than its affinity for PC hexamers containing no linker protein. PBS from a cpcD3 mutant, which lacks the 9-kDa, PC-associated rod linker, incorporated up to six rFNR-3D molecules per PBS. PBS of a cpcC mutant, which has peripheral rods that contain single PC hexamers, also incorporated up to six rFNR-3D molecules per PBS. Direct competition binding experiments showed that PBS from the cpcD3 mutant bound more enzyme than PBS from the cpcC mutant. These observations support the hypothesis that the enzyme binds preferentially to the distal ends of the peripheral rods of the PBS. These data also show that the relative affinity order of the PC complexes for FNR-3D is as follows: (alpha(PC)beta(PC))(6)-L(R)(33) > (alpha(PC)beta(PC))(6)-L(RC)(27) > (alpha(PC)beta(PC))(6). The data suggest that, during the assembly of the PBS, FNR-3D could be displaced to the periphery according to its relative binding affinity for different PC subcomplexes. Thus, FNR-3D would not interfere with the light absorption and energy transfer properties of PC in the peripheral rods of the PBS. The implications of this localization of FNR within the PBS with respect to its function in cyanobacteria are discussed.
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Research Interests: Kinetics, Biology, Cyanobacteria, Biological Chemistry, Medicine, and 14 moreBiological Sciences, DNA, Mutation, Plants, Gene, Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis, CHEMICAL SCIENCES, Molecular weight, Amino Acid Sequence, Base Sequence, Photosystem II, Molecular Sequence Data, Restriction Mapping, and Medical and Health Sciences
Synechococcus sp. PCC 7002 is an ideal model cyanobacterium for functional genomics and biotechnological applications through metabolic engineering. A gene expression system that takes advantage of its multiple, endogenous plasmids has... more
Synechococcus sp. PCC 7002 is an ideal model cyanobacterium for functional genomics and biotechnological applications through metabolic engineering. A gene expression system that takes advantage of its multiple, endogenous plasmids has been constructed in this cyanobacterium. The method involves the integration of foreign DNA cassettes with selectable markers into neutral sites that can be located on any of the several endogenous plasmids of this organism. We have exploited the natural transformability and powerful homologous recombination capacity of this organism by using linear DNA fragments for transformation. This approach overcomes barriers that have made the introduction and expression of foreign genes problematic in the past. Foremost among these is the natural restriction endonuclease barrier that can cleave transforming circular plasmid DNAs before they can be replicated in the cell. We describe herein the general methodology for expressing foreign and homologous genes in Synechococcus sp. PCC 7002, a comparison of several commonly used promoters, and provide examples of how this approach has successfully been used in complementation analyses and overproduction of proteins with affinity tags.
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Cyanobacterium Synechococcus sp. PCC 7002 contains a single gene (glbN) coding for GlbN, a protein of the 2/2 hemoglobin lineage. The precise function of GlbN is not known, but comparison to similar 2/2 hemoglobins suggests that... more
Cyanobacterium Synechococcus sp. PCC 7002 contains a single gene (glbN) coding for GlbN, a protein of the 2/2 hemoglobin lineage. The precise function of GlbN is not known, but comparison to similar 2/2 hemoglobins suggests that reversible dioxygen binding is not its main activity. In this report, the results of in vitro and in vivo experiments probing the role of GlbN are presented. Transcription profiling indicated that glbN is not strongly regulated under any of a large number of growth conditions and that the gene is probably constitutively expressed. High levels of nitrate, used as the sole source of nitrogen, and exposure to nitric oxide were tolerated better by the wild-type strain than a glbN null mutant, whereas overproduction of GlbN in the null mutant background restored the wild-type growth. The cellular contents of reactive oxygen/nitrogen species were elevated in the null mutant under all conditions and were highest under NO challenge or in the presence of high nitrate concentrations. GlbN overproduction attenuated these contents significantly under the latter conditions. The analysis of cell extracts revealed that the heme of GlbN was covalently bound to overproduced GlbN apoprotein in cells grown under microoxic conditions. A peroxidase assay showed that purified GlbN does not possess significant hydrogen peroxidase activity. It was concluded that GlbN protects cells from reactive nitrogen species that could be encountered naturally during growth on nitrate or under denitrifying conditions. The solution structure of covalently modified GlbN was determined and used to rationalize some of its chemical properties.
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Research Interests: Molecular Evolution, Photosynthesis, Plant Biology, Biology, Cyanobacteria, and 15 moreHorizontal Gene Transfer, Medicine, Antibodies, Phylogeny, Animals, Iron, Gene, Gene Duplication, Homeostasis, Acclimatization, Phylogenetic Tree, Rabbits, Photosystem II, Gene expression profiling, and photosystem
PsaE is a small basic subunit located on the stromal (cytoplasmic) side of photosystem I. In cyanobacteria, this subunit participates in cyclic electron transport and modulates the interactions of the complex with soluble ferredoxin. The... more
PsaE is a small basic subunit located on the stromal (cytoplasmic) side of photosystem I. In cyanobacteria, this subunit participates in cyclic electron transport and modulates the interactions of the complex with soluble ferredoxin. The PsaE protein isolated from the cyanobacterium Synechococcus sp. strain PCC 7002 adopts the beta topology of an SH3 domain, with five beta strands (betaA through betaE) and a turn of 3(10) helix between strands betaD and betaE [Falzone, C. J., Kao, Y.-H., Zhao, J., Bryant, D. A., and Lecomte, J. T. J. (1994) Biochemistry 33, 6052-6062]. The primary structure of the PsaE protein is strongly conserved across all oxygen-evolving photosynthetic organisms. However, variability in loop lengths, as well as N- or C-terminal extensions, suggests that the structure of a second representative PsaE subunit would be useful to characterize the interactions among photosystem I polypeptides. In this work, the solution structure of PsaE from the cyanobacterium Nostoc sp. strain PCC 8009 was determined by NMR methods. Compared to PsaE from Synechococcus sp. strain PCC 7002, this PsaE has a seven-residue deletion in the loop connecting strands betaC and betaD, and an eight-residue C-terminal extension. Angular and distance restraints derived from homonuclear and heteronuclear NMR experiments were used to calculate structures by a distance-geometry/simulated-annealing protocol. A family of 20 structures (rmsd of 0.24 A in the regular secondary structure) is presented. Differences between the two cyanobacterial proteins are mostly confined to the CD loop region; the C-terminal extension is disordered. The thermodynamic stability of Nostoc sp. strain PCC 8009 PsaE toward urea denaturation was measured by circular dichroism and fluorescence spectroscopy, and thermal denaturation was monitored by UV absorption spectroscopy. Chemical and thermal denaturation curves are modeled satisfactorily with two-state processes. The DeltaG degrees of unfolding at room temperature is 12.4 +/- 0.3 kJ mol(-1) (pH 5), and the thermal transition midpoint is 59 +/- 1 degrees C (pH 7). Interactions with other proteins in the photosystem I complex may aid in maintaining PsaE in its native state under physiological conditions.
Research Interests: Biochemistry, Thermodynamics, Chemistry, Cyanobacteria, Medicine, and 10 moreMacromolecular X-Ray Crystallography, Urea, photosystem I, Solutions, Amino Acid Sequence, Protein Denaturation, Solution Structure, Biochemistry and cell biology, Molecular Sequence Data, and Medical biochemistry and metabolomics
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Research Interests: Chemistry, Kinetics, Cyanobacteria, Biological Chemistry, Medicine, and 15 moreBiological Sciences, Mutation, Electron Transfer, Chlorophyll, Biological, Light, Electron Transport, photosystem I, CHEMICAL SCIENCES, Electrons, Oxygen, Photosystem II, Dimerization, binding sites, and Medical and Health Sciences
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Cyanobacteria acclimate to low temperature by desaturating their membrane lipids. Mutant strains of Synechococcus sp. PCC 7002 containing insertionally inactivated desA (Delta12 acyl-lipid desaturase) and desB (omega3 acyl-lipid... more
Cyanobacteria acclimate to low temperature by desaturating their membrane lipids. Mutant strains of Synechococcus sp. PCC 7002 containing insertionally inactivated desA (Delta12 acyl-lipid desaturase) and desB (omega3 acyl-lipid desaturase) genes were produced, and their low-temperature susceptibility was characterized. The desA mutant synthesized no linoleic acid or alpha-linolenic acid, and the desB mutant did not produce alpha-linolenic acid. The desA mutant grew more slowly than the wild-type at 22 degrees C and could not grow at 15 degrees C. The desB mutant could not continuously grow at 15 degrees C, although no observable phenotype appeared at higher temperatures. It has been shown that expression of the desA gene occurs at 38 degrees C and is up-regulated at 22 degrees C, and that the desB gene is only expressed at 22 degrees C. These results indicate that the expression of the desA and desB genes occurs at higher temperatures than those at which a significant decline in physiological activities is caused by the absence of their products. The temperature dependency of photosynthesis was not affected by these mutations. Since chlorosis and inability to grow at 15 degrees C with nitrate was suppressed by the substitution of urea as a nitrogen source, it is very likely that the chilling susceptibility of the desaturase mutants is attributable to nutrient limitation.
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... ANALYSES OF CYANOBACTERIAL PHOTOSYSTEM I The Directionality of Electron Transfer Fan Yang, 1 Gaozhong Shen, 2 Wendy M. Schluchter, 2 ... MY and Feher, G.(1995) in Anoxygenic Photosynthetic Bacteria (Blankenship, RE, Madi-gan, MT, and... more
... ANALYSES OF CYANOBACTERIAL PHOTOSYSTEM I The Directionality of Electron Transfer Fan Yang, 1 Gaozhong Shen, 2 Wendy M. Schluchter, 2 ... MY and Feher, G.(1995) in Anoxygenic Photosynthetic Bacteria (Blankenship, RE, Madi-gan, MT, and Bauer, CE eds.), pp. ...
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Research Interests: Engineering, Chemistry, Water, Quantum Theory, Nuclear Magnetic Resonance, and 14 moreCyanobacteria, Chemical Physics, Medicine, Mutation, Physical sciences, Data Reduction, photosystem I, Oxygen Isotopes, CHEMICAL SCIENCES, Biological systems, Molecular weight, Photosystem II, Rate Constant, and nonlinear equation
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Insertional Inactivation of the <i>menG</i> Gene, Encoding 2-Phytyl-1,4-Naphthoquinone Methyltransferase of <i>Synechocystis</i> sp. PCC 6803, Results in the Incorporation of 2-Phytyl-1,4-Naphthoquinone into the A<sub>1</sub> Site and Alteration of the Equilibrium Constant between A<sub>1</sub> a...more
A gene encoding a methyltransferase (menG) was identified in Synechocystis sp. PCC 6803 as responsible for transferring the methyl group to 2-phytyl-1,4-naphthoquinone in the biosynthetic pathway of phylloquinone, the secondary electron... more
A gene encoding a methyltransferase (menG) was identified in Synechocystis sp. PCC 6803 as responsible for transferring the methyl group to 2-phytyl-1,4-naphthoquinone in the biosynthetic pathway of phylloquinone, the secondary electron acceptor in photosystem I (PS I). Mass spectrometric measurements showed that targeted inactivation of the menG gene prevented the methylation step in the synthesis of phylloquinone and led to the accumulation of 2-phytyl-1,4-naphthoquinone in PS I. Growth rates of the wild-type and the menG mutant strains under photoautotrophic and photomixotrophic conditions were virtually identical. The chlorophyll a content of the menG mutant strain was similar to that of wild type when the cells were grown at a light intensity of 50 microE m(-2) s(-1) but was slightly lower when grown at 300 microE m(-2) s(-1). Chlorophyll fluorescence emission measurements at 77 K showed a larger increase in the ratio of PS II to PS I in the menG mutant strain relative to the wild type as the light intensity was elevated from 50 to 300 microE m(-2) s(-1). CW EPR studies at 34 GHz and transient EPR studies at multiple frequencies showed that the quinone radical in the menG mutant has a similar overall line width as that for the wild type, but consistent with the presence of an aromatic proton at ring position 2, the pattern of hyperfine splittings showed two lines in the low-field region. The spin polarization pattern indicated that 2-phytyl-1,4-naphthoquinone is in the same orientation as phylloquinone, and out-of-phase, spin-echo modulation spectroscopy shows the same P700(+) to Q(-) center-to-center distance as in wild-type PS I. Transient EPR studies indicated that the lifetime for forward electron transfer from Q(-) to F(X) is slowed from 290 ns in the wild type to 600 ns in the menG mutant. The redox potential of 2-phytyl-1,4-naphthoquinone is estimated to be 50 to 60 mV more oxidizing than phylloquinone in the A(1) site, which translates to a lowering of the equilibrium constant between Q(-)/Q and F(X)(-)/F(X) by a factor of ca. 10. The lifetime of the P700(+) [F(A)/F(B)](-) backreaction decreased from 80 ms in the wild type to 20 ms in the menG mutant strain and is evidence for a thermally activated, uphill electron transfer through the quinone rather than a direct charge recombination between [F(A)/F(B)](-) and P700(+).
Research Interests: Biochemistry, Chemistry, Fluorescence, Cyanobacteria, Medicine, and 13 moreMutation, Chlorophyll, Methylation, Light, Naphthoquinones, Electron Transport, photosystem I, High Pressure Liquid Chromatography, Oxidation-Reduction, Equilibrium Constant, Methyltransferase, Biochemistry and cell biology, and Medical biochemistry and metabolomics
Research Interests: Chemistry, Crystallography, Kinetics, Mössbauer Spectroscopy, Cyanobacteria, and 15 moreBiological Chemistry, Medicine, Biological Sciences, Temperature, Spectrophotometry, Plasmids, photosystem I, CHEMICAL SCIENCES, Oxygen, Synechococcus, Protein Conformation, P, Electron Paramagnetic Resonance, Medical and Health Sciences, and In Vitro Techniques
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The first attempts to elucidate the molecular mechanisms that function in the bioassembly of the bound Fe/S clusters in Photosystem I (PS I) are discussed. Fe/S proteins participate in a wide variety of processes, the most important of... more
The first attempts to elucidate the molecular mechanisms that function in the bioassembly of the bound Fe/S clusters in Photosystem I (PS I) are discussed. Fe/S proteins participate in a wide variety of processes, the most important of which in photosynthetic organisms are light-mediated electron transport and stress-induced regulation of genes. One of the last steps in the biogenesis of
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Research Interests: Chemistry, Kinetics, Medicine, Macromolecular X-Ray Crystallography, Biological Sciences, and 12 moreMutation, Electron Transfer, Physical sciences, Electron Transport, photosystem I, CHEMICAL SCIENCES, Photochemistry and Photobiology, Time Factors, Kinetic Energy, Synechococcus, Protein Binding, and Oxidation-Reduction
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The issue of whether one or both branches of electron-transfer cofactors is active in Photosystem I (PS I) was studied using a strategy employing interposon mutagenesis and electron paramagnetic resonance (EPR) spectroscopy. PS I... more
The issue of whether one or both branches of electron-transfer cofactors is active in Photosystem I (PS I) was studied using a strategy employing interposon mutagenesis and electron paramagnetic resonance (EPR) spectroscopy. PS I complexes were isolated using n-dodecyl-β-d-...
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The secondary electron acceptor, A1, in Photosystem I (PS I) of cyanobacteria and green plants is phylloquinone (2-methyl-3-phytyl-1, 4-naphthoquinone; Vitamin K,). This cofactor accepts an electron from the primary acceptor, A0, and... more
The secondary electron acceptor, A1, in Photosystem I (PS I) of cyanobacteria and green plants is phylloquinone (2-methyl-3-phytyl-1, 4-naphthoquinone; Vitamin K,). This cofactor accepts an electron from the primary acceptor, A0, and passes it forward to Fx, the first of three cubane iron-sulfur clusters in PS I (see ref. [1] for review). There are reports that electron transfer from A0 to the terminal iron-sulfur clusters occurs with a high quantum yield at cryogenic temperatures after extraction of phylloquinone with 80% water-saturated ether [2,3]. Solvent extraction, however, may lead to ancillary damage such as removal of antenna chlorophylls and s-carotenes, opening the possibility for changes in distances and geometries between the remaining cofactors. The biosynthetic pathway of phylloquinone in Synechocystis sp. PCC 6803 has been identified by analogy with the menaquinone pathway of Escherichia coli. The genes include menB, which codes for naphthoate synthase; menA, which codes for phytyl transferase; and an unidentified gene (menG) which codes for SAM-2-phytyl-1,4-naphthoquinone methyltransferase. We interrupted the menA and menB genes to preclude phylloquinone biosynthesis for the purpose of studying electron transfer through A1. Our expectation was that when the mutant cells were grown the A1 site would be empty, thereby allowing us to study electron transfer from A0 to FX in the absence of a bound quinone.
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The photosystem I (PS I) reaction center is a large multisubunit complex composed of at least eleven polypeptides in cyanobacteria and chloroplasts of higher plants [1]. Six redox centers are involved in light-induced electron transfer... more
The photosystem I (PS I) reaction center is a large multisubunit complex composed of at least eleven polypeptides in cyanobacteria and chloroplasts of higher plants [1]. Six redox centers are involved in light-induced electron transfer from plastocyanin (or cytochrome c6) to ferredoxin (or flavodoxin) in PS I. The PsaA/PsaB heterodimer harbors the primary electron carriers P700 (a chlorophyll (Chl) a dimer), A0 (a monomeric Chl a), A1 (a phylloquinone) and FX (an interpolypeptide [4Fe–4S] cluster). The terminal electron acceptors FA and FB are [4Fe–4S] clusters which are located on the extrinsic PsaC protein. Although significant progress has been achieved in elucidating the structure [2, 3] and function of the PS I, questions still remain concerning the biogenesis, assembly, and regulation of PS I in the membrane. The biogenesis of photosynthetic complexes in cyanobacteria and higher-plant chloroplasts is probably a complex, multi-step process, which is likely to be highly regulated at the post-translation level, especially for cofactor-binding polypeptides. Here we report preliminary results from studies of a gene encoding a novel rubredoxin-like protein with an essential function in the assembly of the FA, FB and FX iron-sulfur clusters in PS I reaction center.
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Research Interests: Chemistry, Kinetics, Cyanobacteria, Biological Chemistry, Medicine, and 15 moreBiological Sciences, Mutation, Electron Transfer, Chlorophyll, Biological, Light, Electron Transport, photosystem I, CHEMICAL SCIENCES, Electrons, Oxygen, Photosystem II, Dimerization, binding sites, and Medical and Health Sciences
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Of all extant environs, iron-depositing hot springs (IDHS) may exhibit the greatest similarity to late Precambrian shallow warm oceans in regards to temperature, O2 gradients and dissolved iron and H2S concentrations. Despite the insights... more
Of all extant environs, iron-depositing hot springs (IDHS) may exhibit the greatest similarity to late Precambrian shallow warm oceans in regards to temperature, O2 gradients and dissolved iron and H2S concentrations. Despite the insights into the ecology, evolutionary biology, paleogeobiochemistry, and astrobiology examination of IDHS could potentially provide, very few studies dedicated to the physiology and diversity of cyanobacteria (CB) inhabiting IDHS have been conducted. Results. Here we describe the phylogeny, physiology, ultrastructure and biogeochemical activity of several recent CB isolates from two different greater Yellowstone area IDHS, LaDuke and Chocolate Pots. Phylogenetic analysis of 16S rRNA genes indicated that 6 of 12 new isolates examined couldn't be placed within established CB genera. Some of the isolates exhibited pronounced requirements for elevated iron concentrations, with maximum growth rates observed when 0.4-1 mM Fe(3+) was present in the media. In light of "typical" CB iron requirements, our results indicate that elevated iron likely represents a salient factor selecting for "siderophilicM CB species in IDHS. A universal feature of our new isolates is their ability to produce thick EPS layers in which iron accumulates resulting in the generation of well preserved signatures. In parallel, siderophilic CB show enhanced ability to etch the analogs of iron-rich lunar regolith minerals and impact glasses. Despite that iron deposition by CB is not well understood mechanistically, we recently obtained evidence that the PS I:PS II ratio is higher in one of our isolates than for other CB. Although still preliminary, this finding is in direct support of the Y. Cohen hypothesis that PSI can directly oxidize Fe(2+). Conclusion. Our results may have implications for factors driving CB evolutionary relationships and biogeochemical processes on early Earth and probably Mars.
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To compete in certain low-light environments, some cyanobacteria express a paralog of the light-harvesting phycobiliprotein, allophycocyanin (AP), that strongly absorbs far-red light (FRL). Using cryo–electron microscopy and time-resolved... more
To compete in certain low-light environments, some cyanobacteria express a paralog of the light-harvesting phycobiliprotein, allophycocyanin (AP), that strongly absorbs far-red light (FRL). Using cryo–electron microscopy and time-resolved absorption spectroscopy, we reveal the structure-function relationship of this FRL-absorbing AP complex (FRL-AP) that is expressed during acclimation to low light and that likely associates with chlorophyll a–containing photosystem I. FRL-AP assembles as helical nanotubes rather than typical toroids due to alterations of the domain geometry within each subunit. Spectroscopic characterization suggests that FRL-AP nanotubes are somewhat inefficient antenna; however, the enhanced ability to harvest FRL when visible light is severely attenuated represents a beneficial trade-off. The results expand the known diversity of light-harvesting proteins in nature and exemplify how biological plasticity is achieved by balancing resource accessibility with effic...
Research Interests: Biophysics and Science
In hyper-arid deserts, endolithic microbial communities survive in the pore spaces and cracks of rocks, an environment that enhances water retention and filters UV radiation. The rock colonization zone is enriched in far-red light (FRL)... more
In hyper-arid deserts, endolithic microbial communities survive in the pore spaces and cracks of rocks, an environment that enhances water retention and filters UV radiation. The rock colonization zone is enriched in far-red light (FRL) and depleted in visible light. This poses a challenge to cyanobacteria, which are the primary producers of endolithic communities. Many species of cyanobacteria are capable of Far-Red-Light Photoacclimation (FaRLiP), a process in which FRL induces the synthesis of specialized chlorophylls and remodeling of the photosynthetic apparatus, providing the ability to grow in FRL. While FaRLiP has been reported in cyanobacteria from various low-light environments, our understanding of light adaptations for endolithic cyanobacteria remains limited. Here, we demonstrated that endolithic Chroococcidiopsis isolates from deserts around the world synthesize chlorophyll f, an FRL-specialized chlorophyll when FRL is the sole light source. The metagenome-assembled ge...