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Lettau E, Lorent C, Appel J, Boehm M, Cordero PRF, Lauterbach L. Insights into electron transfer and bifurcation of the Synechocystis sp. PCC6803 hydrogenase reductase module. BIOCHIMICA ET BIOPHYSICA ACTA. BIOENERGETICS 2025; 1866:149508. [PMID: 39245309 DOI: 10.1016/j.bbabio.2024.149508] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2024] [Revised: 09/03/2024] [Accepted: 09/04/2024] [Indexed: 09/10/2024]
Abstract
The NAD+-reducing soluble [NiFe] hydrogenase (SH) is the key enzyme for production and consumption of molecular hydrogen (H2) in Synechocystis sp. PCC6803. In this study, we focused on the reductase module of the SynSH and investigated the structural and functional aspects of its subunits, particularly the so far elusive role of HoxE. We demonstrated the importance of HoxE for enzyme functionality, suggesting a regulatory role in maintaining enzyme activity and electron supply. Spectroscopic analysis confirmed that HoxE and HoxF each contain one [2Fe2S] cluster with an almost identical electronic structure. Structure predictions, alongside experimental evidence for ferredoxin interactions, revealed a remarkable similarity between SynSH and bifurcating hydrogenases, suggesting a related functional mechanism. Our study unveiled the subunit arrangement and cofactor composition essential for biological electron transfer. These findings enhance our understanding of NAD+-reducing [NiFe] hydrogenases in terms of their physiological function and structural requirements for biotechnologically relevant modifications.
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Affiliation(s)
- Elisabeth Lettau
- RWTH Aachen University, iAMB - Institute of Applied Microbiology, Worringerweg 1, 52074 Aachen, Germany; Technische Universität Berlin, Institute of Chemistry, Straße des 14. Juni 135, 10623 Berlin, Germany.
| | - Christian Lorent
- Technische Universität Berlin, Institute of Chemistry, Straße des 14. Juni 135, 10623 Berlin, Germany
| | - Jens Appel
- Universität Kassel, Molecular Plant Biology, Heinrich-Plett-Straße 40, 34132 Kassel, Germany
| | - Marko Boehm
- Universität Kassel, Molecular Plant Biology, Heinrich-Plett-Straße 40, 34132 Kassel, Germany
| | - Paul R F Cordero
- RWTH Aachen University, iAMB - Institute of Applied Microbiology, Worringerweg 1, 52074 Aachen, Germany
| | - Lars Lauterbach
- RWTH Aachen University, iAMB - Institute of Applied Microbiology, Worringerweg 1, 52074 Aachen, Germany.
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2
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Romig M, Eberwein M, Deobald D, Schmid A. Reactivation and long-term stabilization of the [NiFe] Hox hydrogenase of Synechocystis sp. PCC6803 by glutathione after oxygen exposure. J Biol Chem 2024:108086. [PMID: 39675701 DOI: 10.1016/j.jbc.2024.108086] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2024] [Revised: 11/29/2024] [Accepted: 12/09/2024] [Indexed: 12/17/2024] Open
Abstract
Hydrogenases are key enzymes forming or consuming hydrogen. The inactivation of these transition metal biocatalysts with oxygen limits their biotechnological applications. Oxygen-sensitive hydrogenases are distinguished from oxygen-insensitive (tolerant) ones by their initial hydrogen turnover rates influenced by oxygen. Several hydrogenases, such as the oxygen-sensitive bidirectional [NiFe] Hox hydrogenase (Hox) of the unicellular cyanobacterium Synechocystis sp. PCC6803, are reactivated after oxygen-induced deactivation by redox mechanisms. In cyanobacteria, the glutathione (GSH) redox buffer majorly controls intracellular redox potentials. The relationship between Hox turnover rates and the redox potential in its natural reaction environment is not fully understood. We thus determined hydrogen oxidation rates as activities of Hox in cell-free extracts of Synechocystis using benzyl viologen as artificial electron acceptor. We found that GSH modulates Hox hydrogen oxidation rates under oxygen-free conditions. After oxygen exposure, it influences the maximal turnover rate and aids in the reactivation of Hox. Moreover, GSH stabilizes the long-term Hox activity under anoxic conditions and attenuates oxygen-induced deactivation of Hox in a concentration dependent manner, probably by fostering reactivation. Conversely, oxidized GSH (GSSG) negatively affects Hox activity and oxygen insensitivity. Using Blue Native PAGE followed by mass spectrometry, we showed that oxygen affects Hox complex integrity. The in-silico predicted structure of the Hox complex and complexome analyses reveal the formation of various Hox subcomplexes under different conditions. Our findings refine our current classification of oxygen-hydrogenase interactions beyond sensitive and insensitive, which is particularly important for understanding hydrogenase function under physiological conditions in future.
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Affiliation(s)
- Merle Romig
- Department of Solar Materials Biotechnology, Helmholtz Centre for Environmental Research - UFZ GmbH, Permoserstrasse 15, 04318 Leipzig, Germany
| | - Marie Eberwein
- Department of Molecular Environmental Biotechnology, Helmholtz Centre for Environmental Research - UFZ GmbH, Permoserstrasse 15, 04318 Leipzig, Germany
| | - Darja Deobald
- Department of Molecular Environmental Biotechnology, Helmholtz Centre for Environmental Research - UFZ GmbH, Permoserstrasse 15, 04318 Leipzig, Germany
| | - Andreas Schmid
- Department of Solar Materials Biotechnology, Helmholtz Centre for Environmental Research - UFZ GmbH, Permoserstrasse 15, 04318 Leipzig, Germany
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3
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Blahut MR, Dawson ME, Kisgeropoulos EC, Ledinina AE, Mulder DW, King PW. Functional roles of the [2Fe-2S] clusters in Synechocystis PCC 6803 Hox [NiFe]-hydrogenase reactivity with ferredoxins. J Biol Chem 2024; 300:107936. [PMID: 39476964 DOI: 10.1016/j.jbc.2024.107936] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2024] [Revised: 10/07/2024] [Accepted: 10/21/2024] [Indexed: 12/01/2024] Open
Abstract
The HoxEFUYH complex of Synechocystis PCC 6803 (S. 6803) consists of a HoxEFU ferredoxin:NAD(P)H oxidoreductase subcomplex and a HoxYH [NiFe]-hydrogenase subcomplex that catalyzes reversible H2 oxidation. Prior studies have suggested that the presence of HoxE is required for reactivity with ferredoxin; however, it is unknown how HoxE is functionally integrated into the electron transfer network of the HoxEFU:ferredoxin complex. Deciphering electron transfer pathways is challenged by the rich iron-sulfur cluster content of HoxEFU, which includes a [2Fe-2S] cluster in each subunit, along with multiple [4Fe-4S] clusters and a flavin cofactor. To resolve the role of HoxE, we determined the biophysical and thermodynamic properties of each [2Fe-2S] cluster in HoxEFU using steady-state and potentiometric EPR analysis in combination with square wave voltammetry (SWV). The temperature-dependence of the EPR signal for HoxE confirmed the coordination of a single [2Fe-2S] cluster that was shown by SWV to have an Em = -424 mV (versus SHE). Strikingly, when the Em of the HoxE [2Fe-2S] cluster was analyzed in HoxEFU titrations, it was shifted by >100 mV to an Em < -525 mV (versus SHE). EPR titrations of HoxEFU gave an Em value for the [2Fe-2S] cluster of HoxF, Em = -419 mV and HoxU, Em = -349 mV. These values were used to re-analyze the diaphorase kinetics in reactions performed with ferredoxins with varying Em's. The results are formulated into a model of HoxEFU:ferredoxin reactivity and the role of HoxE in mediating electron transfer within the HoxEFU:ferredoxin complex.
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Affiliation(s)
- Matthew R Blahut
- Biosciences Center, National Renewable Energy Lab, Golden, Colorado, USA
| | - Michael E Dawson
- Biosciences Center, National Renewable Energy Lab, Golden, Colorado, USA
| | | | | | - David W Mulder
- Biosciences Center, National Renewable Energy Lab, Golden, Colorado, USA
| | - Paul W King
- Biosciences Center, National Renewable Energy Lab, Golden, Colorado, USA.
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4
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Evidence for Electron Transfer from the Bidirectional Hydrogenase to the Photosynthetic Complex I (NDH-1) in the Cyanobacterium Synechocystis sp. PCC 6803. Microorganisms 2022; 10:microorganisms10081617. [PMID: 36014035 PMCID: PMC9414918 DOI: 10.3390/microorganisms10081617] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Revised: 08/01/2022] [Accepted: 08/02/2022] [Indexed: 12/12/2022] Open
Abstract
The cyanobacterial bidirectional [NiFe]-hydrogenase is a pentameric enzyme. Apart from the small and large hydrogenase subunits (HoxYH) it contains a diaphorase module (HoxEFU) that interacts with NAD(P)+ and ferredoxin. HoxEFU shows strong similarity to the outermost subunits (NuoEFG) of canonical respiratory complexes I. Photosynthetic complex I (NDH-1) lacks these three subunits. This led to the idea that HoxEFU might interact with NDH-1 instead. HoxEFUYH utilizes excited electrons from PSI for photohydrogen production and it catalyzes the reverse reaction and feeds electrons into the photosynthetic electron transport. We analyzed hydrogenase activity, photohydrogen evolution and hydrogen uptake, the respiration and photosynthetic electron transport of ΔhoxEFUYH, and a knock-out strain with dysfunctional NDH-1 (ΔndhD1/ΔndhD2) of the cyanobacterium Synechocystis sp. PCC 6803. Photohydrogen production was prolonged in ΔndhD1/ΔndhD2 due to diminished hydrogen uptake. Electrons from hydrogen oxidation must follow a different route into the photosynthetic electron transport in this mutant compared to wild type cells. Furthermore, respiration was reduced in ΔhoxEFUYH and the ΔndhD1/ΔndhD2 localization of the hydrogenase to the membrane was impaired. These data indicate that electron transfer from the hydrogenase to the NDH-1 complex is either direct, by the binding of the hydrogenase to the complex, or indirect, via an additional mediator.
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5
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Zuchan K, Baymann F, Baffert C, Brugna M, Nitschke W. The dyad of the Y-junction- and a flavin module unites diverse redox enzymes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2021; 1862:148401. [PMID: 33684340 DOI: 10.1016/j.bbabio.2021.148401] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 08/27/2020] [Revised: 02/09/2021] [Accepted: 02/16/2021] [Indexed: 11/26/2022]
Abstract
The concomitant presence of two distinctive polypeptide modules, which we have chosen to denominate as the "Y-junction" and the "flavin" module, is observed in 3D structures of enzymes as functionally diverse as complex I, NAD(P)-dependent [NiFe]-hydrogenases and NAD(P)-dependent formate dehydrogenases. Amino acid sequence conservation furthermore suggests that both modules are also part of NAD(P)-dependent [FeFe]-hydrogenases for which no 3D structure model is available yet. The flavin module harbours the site of interaction with the substrate NAD(P) which exchanges two electrons with a strictly conserved flavin moiety. The Y-junction module typically contains four iron-sulphur centres arranged to form a Y-shaped electron transfer conduit and mediates electron transfer between the flavin module and the catalytic units of the respective enzymes. The Y-junction module represents an electron transfer hub with three potential electron entry/exit sites. The pattern of specific redox centres present both in the Y-junction and the flavin module is correlated to present knowledge of these enzymes' functional properties. We have searched publicly accessible genomes for gene clusters containing both the Y-junction and the flavin module to assemble a comprehensive picture of the diversity of enzymes harbouring this dyad of modules and to reconstruct their phylogenetic relationships. These analyses indicate the presence of the dyad already in the last universal common ancestor and the emergence of complex I's EFG-module out of a subgroup of NAD(P)- dependent formate dehydrogenases.
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Affiliation(s)
- Kilian Zuchan
- Aix Marseille Univ, CNRS, BIP, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 09, France
| | - Frauke Baymann
- Aix Marseille Univ, CNRS, BIP, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 09, France
| | - Carole Baffert
- Aix Marseille Univ, CNRS, BIP, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 09, France
| | - Myriam Brugna
- Aix Marseille Univ, CNRS, BIP, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 09, France.
| | - Wolfgang Nitschke
- Aix Marseille Univ, CNRS, BIP, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 09, France
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6
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Preissler J, Reeve HA, Zhu T, Nicholson J, Urata K, Lauterbach L, Wong LL, Vincent KA, Lenz O. Dihydrogen‐Driven NADPH Recycling in Imine Reduction and P450‐Catalyzed Oxidations Mediated by an Engineered O
2
‐Tolerant Hydrogenase. ChemCatChem 2020. [DOI: 10.1002/cctc.202000763] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Janina Preissler
- Institute of Chemistry, Biophysical Chemistry Technische Universität Berlin Straße des 17. Juni 135 10623 Berlin Germany
| | - Holly A. Reeve
- Department of Chemistry University of Oxford Inorganic Chemistry Laboratory South Parks Road Oxford OX1 3QR UK
| | - Tianze Zhu
- Department of Chemistry University of Oxford Inorganic Chemistry Laboratory South Parks Road Oxford OX1 3QR UK
| | - Jake Nicholson
- Department of Chemistry University of Oxford Inorganic Chemistry Laboratory South Parks Road Oxford OX1 3QR UK
| | - Kouji Urata
- Department of Chemistry University of Oxford Inorganic Chemistry Laboratory South Parks Road Oxford OX1 3QR UK
| | - Lars Lauterbach
- Institute of Chemistry, Biophysical Chemistry Technische Universität Berlin Straße des 17. Juni 135 10623 Berlin Germany
| | - Luet L. Wong
- Department of Chemistry University of Oxford Inorganic Chemistry Laboratory South Parks Road Oxford OX1 3QR UK
| | - Kylie A. Vincent
- Department of Chemistry University of Oxford Inorganic Chemistry Laboratory South Parks Road Oxford OX1 3QR UK
| | - Oliver Lenz
- Institute of Chemistry, Biophysical Chemistry Technische Universität Berlin Straße des 17. Juni 135 10623 Berlin Germany
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7
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Artz JH, Tokmina-Lukaszewska M, Mulder DW, Lubner CE, Gutekunst K, Appel J, Bothner B, Boehm M, King PW. The structure and reactivity of the HoxEFU complex from the cyanobacterium Synechocystis sp. PCC 6803. J Biol Chem 2020; 295:9445-9454. [PMID: 32409585 PMCID: PMC7363133 DOI: 10.1074/jbc.ra120.013136] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Revised: 05/11/2020] [Indexed: 11/19/2022] Open
Abstract
Cyanobacterial Hox is a [NiFe] hydrogenase that consists of the hydrogen (H2)-activating subunits HoxYH, which form a complex with the HoxEFU assembly to mediate reactions with soluble electron carriers like NAD(P)H and ferredoxin (Fdx), thereby coupling photosynthetic electron transfer to energy-transforming catalytic reactions. Researchers studying the HoxEFUYH complex have observed that HoxEFU can be isolated independently of HoxYH, leading to the hypothesis that HoxEFU is a distinct functional subcomplex rather than an artifact of Hox complex isolation. Moreover, outstanding questions about the reactivity of Hox with natural substrates and the site(s) of substrate interactions and coupling of H2, NAD(P)H, and Fdx remain to be resolved. To address these questions, here we analyzed recombinantly produced HoxEFU by electron paramagnetic resonance spectroscopy and kinetic assays with natural substrates. The purified HoxEFU subcomplex catalyzed electron transfer reactions among NAD(P)H, flavodoxin, and several ferredoxins, thus functioning in vitro as a shuttle among different cyanobacterial pools of reducing equivalents. Both Fdx1-dependent reductions of NAD+ and NADP+ were cooperative. HoxEFU also catalyzed the flavodoxin-dependent reduction of NAD(P)+, Fdx2-dependent oxidation of NADH and Fdx4- and Fdx11-dependent reduction of NAD+. MS-based mapping identified an Fdx1-binding site at the junction of HoxE and HoxF, adjacent to iron-sulfur (FeS) clusters in both subunits. Overall, the reactivity of HoxEFU observed here suggests that it functions in managing peripheral electron flow from photosynthetic electron transfer, findings that reveal detailed insights into how ubiquitous cellular components may be used to allocate energy flow into specific bioenergetic products.
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Affiliation(s)
- Jacob H Artz
- Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado, USA
| | | | - David W Mulder
- Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado, USA
| | - Carolyn E Lubner
- Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado, USA
| | | | - Jens Appel
- Botanical Institute, Christian-Albrechts-University, Kiel, Germany
| | - Brian Bothner
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana, USA
| | - Marko Boehm
- Botanical Institute, Christian-Albrechts-University, Kiel, Germany
| | - Paul W King
- Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado, USA
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8
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Shomura Y, Taketa M, Nakashima H, Tai H, Nakagawa H, Ikeda Y, Ishii M, Igarashi Y, Nishihara H, Yoon KS, Ogo S, Hirota S, Higuchi Y. Structural basis of the redox switches in the NAD +-reducing soluble [NiFe]-hydrogenase. Science 2018; 357:928-932. [PMID: 28860386 DOI: 10.1126/science.aan4497] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2017] [Accepted: 08/03/2017] [Indexed: 11/03/2022]
Abstract
NAD+ (oxidized form of NAD:nicotinamide adenine dinucleotide)-reducing soluble [NiFe]-hydrogenase (SH) is phylogenetically related to NADH (reduced form of NAD+):quinone oxidoreductase (complex I), but the geometrical arrangements of the subunits and Fe-S clusters are unclear. Here, we describe the crystal structures of SH in the oxidized and reduced states. The cluster arrangement is similar to that of complex I, but the subunits orientation is not, which supports the hypothesis that subunits evolved as prebuilt modules. The oxidized active site includes a six-coordinate Ni, which is unprecedented for hydrogenases, whose coordination geometry would prevent O2 from approaching. In the reduced state showing the normal active site structure without a physiological electron acceptor, the flavin mononucleotide cofactor is dissociated, which may be caused by the oxidation state change of nearby Fe-S clusters and may suppress production of reactive oxygen species.
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Affiliation(s)
- Y Shomura
- Institute of Quantum Beam Science, Graduate School of Science and Engineering, Ibaraki University, 4-12-1 Nakanarusawa, Hitachi, Ibaraki 316-8511, Japan.
| | - M Taketa
- Department of Picobiology, Graduate School of Life Science, University of Hyogo, 3-2-1 Koto, Kamigori-cho, Ako-gun, Hyogo 678-1297, Japan.,Core Research for Evolutional Science and Technology (CREST), Japan and Science Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - H Nakashima
- Department of Picobiology, Graduate School of Life Science, University of Hyogo, 3-2-1 Koto, Kamigori-cho, Ako-gun, Hyogo 678-1297, Japan
| | - H Tai
- Core Research for Evolutional Science and Technology (CREST), Japan and Science Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.,Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama-cho, Ikoma, Nara 630-0192, Japan
| | - H Nakagawa
- Department of Picobiology, Graduate School of Life Science, University of Hyogo, 3-2-1 Koto, Kamigori-cho, Ako-gun, Hyogo 678-1297, Japan
| | - Y Ikeda
- Department of Picobiology, Graduate School of Life Science, University of Hyogo, 3-2-1 Koto, Kamigori-cho, Ako-gun, Hyogo 678-1297, Japan
| | - M Ishii
- Department of Biotechnology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Y Igarashi
- Department of Biotechnology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
| | - H Nishihara
- Department of Bioresource Science, College of Agriculture, Ibaraki University, 3-21-1, Chu-ou, Ami, Ibaraki 300-0393, Japan
| | - K-S Yoon
- World Premier International Research Center Initiative-International Institute for Carbon Neutral Energy Research (WPI-ICNER), Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka 819-0395, Japan.,SPring-8 Center, RIKEN, 1-1-1 Koto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
| | - S Ogo
- World Premier International Research Center Initiative-International Institute for Carbon Neutral Energy Research (WPI-ICNER), Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka 819-0395, Japan.,SPring-8 Center, RIKEN, 1-1-1 Koto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
| | - S Hirota
- Core Research for Evolutional Science and Technology (CREST), Japan and Science Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.,Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama-cho, Ikoma, Nara 630-0192, Japan
| | - Y Higuchi
- Department of Picobiology, Graduate School of Life Science, University of Hyogo, 3-2-1 Koto, Kamigori-cho, Ako-gun, Hyogo 678-1297, Japan. .,Core Research for Evolutional Science and Technology (CREST), Japan and Science Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.,SPring-8 Center, RIKEN, 1-1-1 Koto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
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9
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Rewiring of Cyanobacterial Metabolism for Hydrogen Production: Synthetic Biology Approaches and Challenges. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018; 1080:171-213. [PMID: 30091096 DOI: 10.1007/978-981-13-0854-3_8] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/06/2022]
Abstract
With the demand for renewable energy growing, hydrogen (H2) is becoming an attractive energy carrier. Developing H2 production technologies with near-net zero carbon emissions is a major challenge for the "H2 economy." Certain cyanobacteria inherently possess enzymes, nitrogenases, and bidirectional hydrogenases that are capable of H2 evolution using sunlight, making them ideal cell factories for photocatalytic conversion of water to H2. With the advances in synthetic biology, cyanobacteria are currently being developed as a "plug and play" chassis to produce H2. This chapter describes the metabolic pathways involved and the theoretical limits to cyanobacterial H2 production and summarizes the metabolic engineering technologies pursued.
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10
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Khetkorn W, Rastogi RP, Incharoensakdi A, Lindblad P, Madamwar D, Pandey A, Larroche C. Microalgal hydrogen production - A review. BIORESOURCE TECHNOLOGY 2017; 243:1194-1206. [PMID: 28774676 DOI: 10.1016/j.biortech.2017.07.085] [Citation(s) in RCA: 96] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2017] [Revised: 07/13/2017] [Accepted: 07/17/2017] [Indexed: 06/07/2023]
Abstract
Bio-hydrogen from microalgae including cyanobacteria has attracted commercial awareness due to its potential as an alternative, reliable and renewable energy source. Photosynthetic hydrogen production from microalgae can be interesting and promising options for clean energy. Advances in hydrogen-fuel-cell technology may attest an eco-friendly way of biofuel production, since, the use of H2 to generate electricity releases only water as a by-product. Progress in genetic/metabolic engineering may significantly enhance the photobiological hydrogen production from microalgae. Manipulation of competing metabolic pathways by modulating the certain key enzymes such as hydrogenase and nitrogenase may enhance the evolution of H2 from photoautotrophic cells. Moreover, biological H2 production at low operating costs is requisite for economic viability. Several photobioreactors have been developed for large-scale biomass and hydrogen production. This review highlights the recent technological progress, enzymes involved and genetic as well as metabolic engineering approaches towards sustainable hydrogen production from microalgae.
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Affiliation(s)
- Wanthanee Khetkorn
- Division of Biology, Faculty of Science and Technology, Rajamangala University of Technology Thanyaburi, Thanyaburi, Pathumthani 12110, Thailand
| | - Rajesh P Rastogi
- Ministry of Environment, Forest and Climate Change, Indira Paryavaran Bhawan, Jor Bagh Road, New Delhi 110 003, India.
| | - Aran Incharoensakdi
- Laboratory of Cyanobacterial Biotechnology, Department of Biochemistry, Faculty of Science, Chulalongkorn University, Phayathai Road, Bangkok 10330, Thailand
| | - Peter Lindblad
- Microbial Chemistry, Department of Chemistry-Ångström, Uppsala University, Box 523, SE-75120 Uppsala, Sweden
| | - Datta Madamwar
- Department of Biosciences, UGC-Centre of Advanced Study, Sardar Patel University, Vadtal Road, Satellite Campus, Bakrol, Anand, Gujarat 388 315, India
| | - Ashok Pandey
- Center of Innovative and Applied Bioprocessing, C-127 2nd Floor Phase 8 Industrial Area, SAS Nagar, Mohali 160 071, Punjab, India
| | - Christian Larroche
- Labex IMobS3 and Institut Pascal, 4 Avenue Blaise Pascal, TSA 60026/CS 60026, 63178 Aubière Cedex, France
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11
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Type II Toxin-Antitoxin Systems in the Unicellular Cyanobacterium Synechocystis sp. PCC 6803. Toxins (Basel) 2016; 8:toxins8070228. [PMID: 27455323 PMCID: PMC4963859 DOI: 10.3390/toxins8070228] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2016] [Accepted: 07/11/2016] [Indexed: 12/03/2022] Open
Abstract
Bacterial toxin–antitoxin (TA) systems are genetic elements, which are encoded by plasmid as well as chromosomal loci. They mediate plasmid and genomic island maintenance through post-segregational killing mechanisms but may also have milder effects, acting as mobile stress response systems that help certain cells of a population in persisting adverse growth conditions. Very few cyanobacterial TA system have been characterized thus far. In this work, we focus on the cyanobacterium Synechocystis 6803, a widely used model organism. We expand the number of putative Type II TA systems from 36 to 69 plus seven stand-alone components. Forty-seven TA pairs are located on the chromosome and 22 are plasmid-located. Different types of toxins are associated with various antitoxins in a mix and match principle. According to protein domains and experimental data, 81% of all toxins in Synechocystis 6803 likely exhibit RNase activity, suggesting extensive potential for toxicity-related RNA degradation and toxin-mediated transcriptome remodeling. Of particular interest is the Ssr8013–Slr8014 system encoded on plasmid pSYSG, which is part of a larger defense island or the pSYSX system Slr6056–Slr6057, which is linked to a bacterial ubiquitin-like system. Consequently, Synechocystis 6803 is one of the most prolific sources of new information about these genetic elements.
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12
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Qian X, Kumaraswamy GK, Zhang S, Gates C, Ananyev GM, Bryant DA, Dismukes GC. Inactivation of nitrate reductase alters metabolic branching of carbohydrate fermentation in the cyanobacterium Synechococcus sp. strain PCC 7002. Biotechnol Bioeng 2015; 113:979-88. [PMID: 26479976 DOI: 10.1002/bit.25862] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Revised: 10/07/2015] [Accepted: 10/13/2015] [Indexed: 11/07/2022]
Abstract
To produce cellular energy, cyanobacteria reduce nitrate as the preferred pathway over proton reduction (H2 evolution) by catabolizing glycogen under dark anaerobic conditions. This competition lowers H2 production by consuming a large fraction of the reducing equivalents (NADPH and NADH). To eliminate this competition, we constructed a knockout mutant of nitrate reductase, encoded by narB, in Synechococcus sp. PCC 7002. As expected, ΔnarB was able to take up intracellular nitrate but was unable to reduce it to nitrite or ammonia, and was unable to grow photoautotrophically on nitrate. During photoautotrophic growth on urea, ΔnarB significantly redirects biomass accumulation into glycogen at the expense of protein accumulation. During subsequent dark fermentation, metabolite concentrations--both the adenylate cellular energy charge (∼ATP) and the redox poise (NAD(P)H/NAD(P))--were independent of nitrate availability in ΔnarB, in contrast to the wild type (WT) control. The ΔnarB strain diverted more reducing equivalents from glycogen catabolism into reduced products, mainly H2 and d-lactate, by 6-fold (2.8% yield) and 2-fold (82.3% yield), respectively, than WT. Continuous removal of H2 from the fermentation medium (milking) further boosted net H2 production by 7-fold in ΔnarB, at the expense of less excreted lactate, resulting in a 49-fold combined increase in the net H2 evolution rate during 2 days of fermentation compared to the WT. The absence of nitrate reductase eliminated the inductive effect of nitrate addition on rerouting carbohydrate catabolism from glycolysis to the oxidative pentose phosphate (OPP) pathway, indicating that intracellular redox poise and not nitrate itself acts as the control switch for carbon flux branching between pathways.
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Affiliation(s)
- Xiao Qian
- Waksman Institute, Rutgers University, New Brunswick, New Jersey.,Department of Microbiology and Biochemistry, Rutgers University, New Brunswick, New Jersey
| | | | - Shuyi Zhang
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, Pennsylvania
| | - Colin Gates
- Waksman Institute, Rutgers University, New Brunswick, New Jersey
| | | | - Donald A Bryant
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, Pennsylvania.,Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana
| | - G Charles Dismukes
- Waksman Institute, Rutgers University, New Brunswick, New Jersey. .,Department of Chemistry and Biological Chemistry, Rutgers University, New Brunswick, New Jersey, 08901.
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13
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Photosynthetic, respiratory and extracellular electron transport pathways in cyanobacteria. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1857:247-55. [PMID: 26498190 DOI: 10.1016/j.bbabio.2015.10.007] [Citation(s) in RCA: 122] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2015] [Revised: 10/09/2015] [Accepted: 10/14/2015] [Indexed: 01/05/2023]
Abstract
Cyanobacteria have evolved elaborate electron transport pathways to carry out photosynthesis and respiration, and to dissipate excess energy in order to limit cellular damage. Our understanding of the complexity of these systems and their role in allowing cyanobacteria to cope with varying environmental conditions is rapidly improving, but many questions remain. We summarize current knowledge of cyanobacterial electron transport pathways, including the possible roles of alternative pathways in photoprotection. We describe extracellular electron transport, which is as yet poorly understood. Biological photovoltaic devices, which measure electron output from cells, and which have been proposed as possible means of renewable energy generation, may be valuable tools in understanding cyanobacterial electron transfer pathways, and enhanced understanding of electron transfer may allow improvements in the efficiency of power output. This article is part of a Special Issue entitled Organization and dynamics of bioenergetic systems in bacteria, edited by Conrad Mullineaux.
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14
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Ghirardi ML. Implementation of photobiological H2 production: the O 2 sensitivity of hydrogenases. PHOTOSYNTHESIS RESEARCH 2015; 125:383-93. [PMID: 26022106 DOI: 10.1007/s11120-015-0158-1] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2015] [Accepted: 05/13/2015] [Indexed: 05/10/2023]
Abstract
The search for the ultimate carbon-free fuel has intensified in recent years, with a major focus on photoproduction of H2. Biological sources of H2 include oxygenic photosynthetic green algae and cyanobacteria, both of which contain hydrogenase enzymes. Although algal and cyanobacterial hydrogenases perform the same enzymatic reaction through metallo-clusters, their hydrogenases have evolved separately, are expressed differently (transcription of algal hydrogenases is anaerobically induced, while bacterial hydrogenases are constitutively expressed), and display different sensitivity to O2 inactivation. Among various physiological factors, the sensitivity of hydrogenases to O2 has been one of the major factors preventing implementation of biological systems for commercial production of renewable H2. This review addresses recent strategies aimed at engineering increased O2 tolerance into hydrogenases (as of now mainly unsuccessful), as well as towards the development of methods to bypass the O2 sensitivity of hydrogenases (successful but still yielding low solar conversion efficiencies). The author concludes with a description of current approaches from various laboratories to incorporate multiple genetic traits into either algae or cyanobacteria to jointly address limiting factors other than the hydrogenase O2 sensitivity and achieve more sustained H2 photoproduction activity.
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Affiliation(s)
- Maria L Ghirardi
- National Renewable Energy Laboratory, 15013 Denver West Pkway, Golden, CO, 80401, USA,
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15
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[NiFe]-hydrogenase is essential for cyanobacterium Synechocystis sp. PCC 6803 aerobic growth in the dark. Sci Rep 2015. [PMID: 26215212 PMCID: PMC4517062 DOI: 10.1038/srep12424] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The cyanobacterium Synechocystis sp. PCC 6803 has a bidirectional [NiFe]-hydrogenase (Hox hydrogenase) which reversibly reduces protons to H2. This enzyme is composed of a hydrogenase domain and a diaphorase moiety, which is distinctly homologous to the NADH input module of mitochondrial respiratory Complex I. Hox hydrogenase physiological function is still unclear, since it is not required for Synechocystis fitness under standard growth conditions. We analyzed the phenotype under prolonged darkness of three Synechocystis knock-out strains, lacking either Hox hydrogenase (ΔHoxE-H) or one of the proteins responsible for the assembly of its NiFe active site (ΔHypA1 and ΔHypB1). We found that Hox hydrogenase is required for Synechocystis growth under this condition, regardless of the functional status of its catalytic site, suggesting an additional role beside hydrogen metabolism. Moreover, quantitative proteomic analyses revealed that the expression levels of several subunits of the respiratory NADPH/plastoquinone oxidoreductase (NDH-1) are reduced when Synechocystis is grown in the dark. Our findings suggest that the Hox hydrogenase could contribute to electron transport regulation when both photosynthetic and respiratory pathways are down-regulated, and provide a possible explanation for the close evolutionary relationship between mitochondrial respiratory Complex I and cyanobacterial [NiFe]-hydrogenases.
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16
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Khanna N, Lindblad P. Cyanobacterial hydrogenases and hydrogen metabolism revisited: recent progress and future prospects. Int J Mol Sci 2015; 16:10537-61. [PMID: 26006225 PMCID: PMC4463661 DOI: 10.3390/ijms160510537] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2015] [Revised: 04/29/2015] [Accepted: 04/30/2015] [Indexed: 11/25/2022] Open
Abstract
Cyanobacteria have garnered interest as potential cell factories for hydrogen production. In conjunction with photosynthesis, these organisms can utilize inexpensive inorganic substrates and solar energy for simultaneous biosynthesis and hydrogen evolution. However, the hydrogen yield associated with these organisms remains far too low to compete with the existing chemical processes. Our limited understanding of the cellular hydrogen production pathway is a primary setback in the potential scale-up of this process. In this regard, the present review discusses the recent insight around ferredoxin/flavodoxin as the likely electron donor to the bidirectional Hox hydrogenase instead of the generally accepted NAD(P)H. This may have far reaching implications in powering solar driven hydrogen production. However, it is evident that a successful hydrogen-producing candidate would likely integrate enzymatic traits from different species. Engineering the [NiFe] hydrogenases for optimal catalytic efficiency or expression of a high turnover [FeFe] hydrogenase in these photo-autotrophs may facilitate the development of strains to reach target levels of biohydrogen production in cyanobacteria. The fundamental advancements achieved in these fields are also summarized in this review.
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Affiliation(s)
- Namita Khanna
- Microbial Chemistry, Department of Chemistry-Ångström Laboratory, Uppsala University, Box 523, Uppsala SE-75120, Sweden.
| | - Peter Lindblad
- Microbial Chemistry, Department of Chemistry-Ångström Laboratory, Uppsala University, Box 523, Uppsala SE-75120, Sweden.
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17
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Burroughs NJ, Boehm M, Eckert C, Mastroianni G, Spence EM, Yu J, Nixon PJ, Appel J, Mullineaux CW, Bryan SJ. Solar powered biohydrogen production requires specific localization of the hydrogenase. ENERGY & ENVIRONMENTAL SCIENCE 2014; 7:3791-3800. [PMID: 26339289 PMCID: PMC4535174 DOI: 10.1039/c4ee02502d] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2014] [Accepted: 09/04/2014] [Indexed: 05/15/2023]
Abstract
Cyanobacteria contain a bidirectional [NiFe] hydrogenase which transiently produces hydrogen upon exposure of anoxic cells to light, potentially acting as a "valve" releasing excess electrons from the electron transport chain. However, its interaction with the photosynthetic electron transport chain remains unclear. By GFP-tagging the HoxF diaphorase subunit we show that the hydrogenase is thylakoid associated, comprising a population dispersed uniformly through the thylakoids and a subpopulation localized to discrete puncta in the distal thylakoid. Thylakoid localisation of both the HoxH and HoxY hydrogenase subunits is confirmed by immunogold electron microscopy. The diaphorase HoxE subunit is essential for recruitment to the dispersed thylakoid population, potentially anchoring the hydrogenase to the membrane, but aggregation to puncta occurs through a distinct HoxE-independent mechanism. Membrane association does not require NDH-1. Localization is dynamic on a scale of minutes, with anoxia and high light inducing a significant redistribution between these populations in favour of puncta. Since HoxE is essential for access to its electron donor, electron supply to the hydrogenase depends on a physiologically controlled localization, potentially offering a new avenue to enhance photosynthetic hydrogen production by exploiting localization/aggregation signals.
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Affiliation(s)
- Nigel J Burroughs
- Systems Biology Centre , Coventry House , University of Warwick , Coventry , CV4 7AL , UK
| | - Marko Boehm
- Imperial College London , South Kensington Campus , London , SW7 2AZ , UK
| | - Carrie Eckert
- Biosciences Centre , National Renewable Energy Laboratory , Golden , Colorado 80401 , USA ; Renewable and Sustainable Energy Institute, University of Colorado Boulder , Boulder , CO 80309 , USA
| | - Giulia Mastroianni
- School of Biological and Chemical Sciences , Queen Mary University of London , Mile End Road , London , E1 4NS , UK .
| | - Edward M Spence
- Pharmaceutical Science Division , King's College London , Franklin-Wilkins Building, 150 Stamford Street , London , SE1 9NH , UK
| | - Jianfeng Yu
- Imperial College London , South Kensington Campus , London , SW7 2AZ , UK
| | - Peter J Nixon
- Imperial College London , South Kensington Campus , London , SW7 2AZ , UK
| | - Jens Appel
- Botanical Institute , University of Kiel , Am Botanischen Garten 1-9 , 24118 Kiel , Germany
| | - Conrad W Mullineaux
- School of Biological and Chemical Sciences , Queen Mary University of London , Mile End Road , London , E1 4NS , UK .
| | - Samantha J Bryan
- School of Biological and Chemical Sciences , Queen Mary University of London , Mile End Road , London , E1 4NS , UK .
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18
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Engineering Synechocystis PCC6803 for hydrogen production: influence on the tolerance to oxidative and sugar stresses. PLoS One 2014; 9:e89372. [PMID: 24586727 PMCID: PMC3933540 DOI: 10.1371/journal.pone.0089372] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2013] [Accepted: 01/20/2014] [Indexed: 11/23/2022] Open
Abstract
In the prospect of engineering cyanobacteria for the biological photoproduction of hydrogen, we have studied the hydrogen production machine in the model unicellular strain Synechocystis PCC6803 through gene deletion, and overexpression (constitutive or controlled by the growth temperature). We demonstrate that the hydrogenase-encoding hoxEFUYH operon is dispensable to standard photoautotrophic growth in absence of stress, and it operates in cell defense against oxidative (H2O2) and sugar (glucose and glycerol) stresses. Furthermore, we showed that the simultaneous over-production of the proteins HoxEFUYH and HypABCDE (assembly of hydrogenase), combined to an increase in nickel availability, led to an approximately 20-fold increase in the level of active hydrogenase. These novel results and mutants have major implications for those interested in hydrogenase, hydrogen production and redox metabolism, and their connections with environmental conditions.
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19
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Gutekunst K, Chen X, Schreiber K, Kaspar U, Makam S, Appel J. The bidirectional NiFe-hydrogenase in Synechocystis sp. PCC 6803 is reduced by flavodoxin and ferredoxin and is essential under mixotrophic, nitrate-limiting conditions. J Biol Chem 2013; 289:1930-7. [PMID: 24311779 DOI: 10.1074/jbc.m113.526376] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cyanobacteria are able to use solar energy for the production of hydrogen. It is generally accepted that cyanobacterial NiFe-hydrogenases are reduced by NAD(P)H. This is in conflict with thermodynamic considerations, as the midpoint potentials of NAD(P)H do not suffice to support the measured hydrogen production under physiological conditions. We show that flavodoxin and ferredoxin directly reduce the bidirectional NiFe-hydrogenase of Synechocystis sp. PCC 6803 in vitro. A merodiploid ferredoxin-NADP reductase mutant produced correspondingly more photohydrogen. We furthermore found that the hydrogenase receives its electrons via pyruvate:flavodoxin/ferredoxin oxidoreductase (PFOR)-flavodoxin/ferredoxin under fermentative conditions, enabling the cells to gain ATP. These results strongly support that the bidirectional NiFe-hydrogenases in cyanobacteria function as electron sinks for low potential electrons from photosystem I and as a redox balancing device under fermentative conditions. However, the selective advantage of this enzyme is not known. No strong phenotype of mutants lacking the hydrogenase has been found. Because bidirectional hydrogenases are widespread in aquatic nutrient-rich environments that are capable of triggering phytoplankton blooms, we mimicked those conditions by growing cells in the presence of increased amounts of dissolved organic carbon and dissolved organic nitrogen. Under these conditions the hydrogenase was found to be essential. As these conditions close the two most important sinks for reduced flavodoxin/ferredoxin (CO2-fixation and nitrate reduction), this discovery further substantiates the connection between flavodoxin/ferredoxin and the NiFe-hydrogenase.
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Affiliation(s)
- Kirstin Gutekunst
- From the Botanical Institute, Christian-Albrechts-University, 24118 Kiel, Germany and
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20
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Eckert C, Boehm M, Carrieri D, Yu J, Dubini A, Nixon PJ, Maness PC. Genetic analysis of the Hox hydrogenase in the cyanobacterium Synechocystis sp. PCC 6803 reveals subunit roles in association, assembly, maturation, and function. J Biol Chem 2012; 287:43502-15. [PMID: 23139416 DOI: 10.1074/jbc.m112.392407] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Hydrogenases are metalloenzymes that catalyze 2H(+) + 2e(-) ↔ H(2). A multisubunit, bidirectional [NiFe]-hydrogenase has been identified and characterized in a number of bacteria, including cyanobacteria, where it is hypothesized to function as an electron valve, balancing reductant in the cell. In cyanobacteria, this Hox hydrogenase consists of five proteins in two functional moieties: a hydrogenase moiety (HoxYH) with homology to heterodimeric [NiFe]-hydrogenases and a diaphorase moiety (HoxEFU) with homology to NuoEFG of respiratory Complex I, linking NAD(P)H ↔ NAD(P)(+) as a source/sink for electrons. Here, we present an extensive study of Hox hydrogenase in the cyanobacterium Synechocystis sp. PCC 6803. We identify the presence of HoxEFUYH, HoxFUYH, HoxEFU, HoxFU, and HoxYH subcomplexes as well as association of the immature, unprocessed large subunit (HoxH) with other Hox subunits and unidentified factors, providing a basis for understanding Hox maturation and assembly. The analysis of mutants containing individual and combined hox gene deletions in a common parental strain reveals apparent alterations in subunit abundance and highlights an essential role for HoxF and HoxU in complex/subcomplex association. In addition, analysis of individual and combined hox mutant phenotypes in a single strain background provides a clear view of the function of each subunit in hydrogenase activity and presents evidence that its physiological function is more complicated than previously reported, with no outward defects apparent in growth or photosynthesis under various growth conditions.
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Affiliation(s)
- Carrie Eckert
- Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, USA.
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21
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The AbrB2 autorepressor, expressed from an atypical promoter, represses the hydrogenase operon to regulate hydrogen production in Synechocystis strain PCC6803. J Bacteriol 2012; 194:5423-33. [PMID: 22865847 DOI: 10.1128/jb.00543-12] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
We have thoroughly investigated the abrB2 gene (sll0822) encoding an AbrB-like regulator in the wild-type strain of the model cyanobacterium Synechocystis strain PCC6803. We report that abrB2 is expressed from an active but atypical promoter that possesses an extended -10 element (TGTAATAT) that compensates for the absence of a -35 box. Strengthening the biological significance of these data, we found that the occurrence of an extended -10 promoter box and the absence of a -35 element are two well-conserved features in abrB2 genes from other cyanobacteria. We also show that AbrB2 is an autorepressor that is dispensable to cell growth under standard laboratory conditions. Furthermore, we demonstrate that AbrB2 also represses the hox operon, which encodes the Ni-Fe hydrogenase of biotechnological interest, and that the hox operon is weakly expressed even though it possesses the two sequences resembling canonical -10 and -35 promoter boxes. In both the AbrB2-repressed promoters of the abrB2 gene and the hox operon, we found a repeated DNA motif [TT-(N(5))-AAC], which could be involved in AbrB2 repression. Supporting this hypothesis, we found that a TT-to-GG mutation of one of these elements increased the activity of the abrB2 promoter. We think that our abrB2-deleted mutant with increased expression of the hox operon and hydrogenase activity, together with the reporter plasmids we constructed to analyze the abrB2 gene and the hox operon, will serve as useful tools to decipher the function and the regulation of hydrogen production in Synechocystis.
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