1
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Yang Y, Lu Z, Azari M, Kartal B, Du H, Cai M, Herbold CW, Ding X, Denecke M, Li X, Li M, Gu JD. Discovery of a new genus of anaerobic ammonium oxidizing bacteria with a mechanism for oxygen tolerance. WATER RESEARCH 2022; 226:119165. [PMID: 36257158 DOI: 10.1016/j.watres.2022.119165] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2022] [Revised: 09/15/2022] [Accepted: 09/23/2022] [Indexed: 06/16/2023]
Abstract
In the past 20 years, there has been a major stride in understanding the core mechanism of anaerobic ammonium-oxidizing (anammox) bacteria, but there are still several discussion points on their survival strategies. Here, we discovered a new genus of anammox bacteria in a full-scale wastewater-treating biofilm system, tentatively named "Candidatus Loosdrechtia aerotolerans". Next to genes of all core anammox metabolisms, it encoded and transcribed genes involved in the dissimilatory nitrate reduction to ammonium (DNRA), which coupled to oxidation of small organic acids, could be used to replenish ammonium and sustain their metabolism. Surprisingly, it uniquely harbored a new ferredoxin-dependent nitrate reductase, which has not yet been found in any other anammox genome and might confer a selective advantage to it in nitrate assimilation. Similar to many other microorganisms, superoxide dismutase and catalase related to oxidative stress resistance were encoded and transcribed by "Ca. Loosdrechtia aerotolerans". Interestingly, bilirubin oxidase (BOD), likely involved in oxygen resistance of anammox bacteria under fluctuating oxygen concentrations, was identified in "Ca. Loosdrechtia aerotolerans" and four Ca. Brocadia genomes, and its activity was demonstrated using purified heterologously expressed proteins. A following survey of oxygen-active proteins in anammox bacteria revealed the presence of other previously undetected oxygen defense systems. The novel cbb3-type cytochrome c oxidase and bifunctional catalase-peroxidase may confer a selective advantage to Ca. Kuenenia and Ca. Scalindua that face frequent changes in oxygen concentrations. The discovery of this new genus significantly broadens our understanding of the ecophysiology of anammox bacteria. Furthermore, the diverse oxygen tolerance strategies employed by distinct anammox bacteria advance our understanding of their niche adaptability and provide valuable insight for the operation of anammox-based wastewater treatment systems.
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Affiliation(s)
- Yuchun Yang
- State Key Laboratory of Biocontrol, School of Ecology, Sun Yat-Sen University, Guangzhou 510275, People's Republic of China
| | - Zhongyi Lu
- Shenzhen Key Laboratory of Marine Microbiome Engineering, Institute for Advanced Study, Shenzhen University, Shenzhen 518060, People's Republic of China; Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, People's Republic of China
| | - Mohammad Azari
- Department of Aquatic Environmental Engineering, Institute for Water and River Basin Management, Karlsruhe Institute of Technology (KIT), Gotthard-Franz-Str. 3, Karlsruhe 76131, Germany
| | - Boran Kartal
- Microbial Physiology Group, Max Planck Institute for Marine Microbiology, Celsiusstraße 1, Bremen 28359, Germany
| | - Huan Du
- Shenzhen Key Laboratory of Marine Microbiome Engineering, Institute for Advanced Study, Shenzhen University, Shenzhen 518060, People's Republic of China
| | - Mingwei Cai
- Shenzhen Key Laboratory of Marine Microbiome Engineering, Institute for Advanced Study, Shenzhen University, Shenzhen 518060, People's Republic of China
| | - Craig W Herbold
- Centre for Microbiology and Environmental Systems Science, Division of Microbial Ecology, University of Vienna, Althanstrasse 14, Vienna 1090, Austria
| | - Xinghua Ding
- Laboratory of Environmental Microbiology and Toxicology, School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, People's Republic of China
| | - Martin Denecke
- Department of Urban Water- and Waste Management, University of Duisburg-Essen, Universitätsstraße 15, Essen 45141, Germany
| | - Xiaoyan Li
- Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, People's Republic of China
| | - Meng Li
- Shenzhen Key Laboratory of Marine Microbiome Engineering, Institute for Advanced Study, Shenzhen University, Shenzhen 518060, People's Republic of China
| | - Ji-Dong Gu
- Environmental Science and Engineering Research Group, Guangdong Technion - Israel Institute of Technology, 241 Daxue Road, Shantou, Guangdong 515063, People's Republic of China; Southern Laboratory of Ocean Science and Engineering (Guangdong, Zhuhai), Zhuhai, Guangdong 519082, People's Republic of China; Guangdong Provincial Key Laboratory of Materials and Technologies for Energy Conversion, Guangdong Technion - Israel Institute of Technology, 241 Daxue Road, Shantou, Guangdong 515063, People's Republic of China.
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2
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Srivastava AP, Mishra N, Prasad RLA, Rajesh P, Knaff DB. Thermodynamics of ferredoxin binding to cyanobacterial nitrate reductase. PHOTOSYNTHESIS RESEARCH 2020; 144:73-84. [PMID: 32222887 DOI: 10.1007/s11120-020-00738-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2019] [Accepted: 03/20/2020] [Indexed: 06/10/2023]
Abstract
The role of the seven negatively charged amino acids of Synechocystis sp. PCC 6803 ferredoxin (Fd), i.e., Glu29, Glu30, Asp60, Asp65, Asp66, Glu92, and Glu93, predicted to form complex with nitrate reductase (NR), was investigated using site-directed mutagenesis and isothermal titration calorimetry (ITC). These experiments identified four Fd amino acids, i.e., Glu29, Asp60, Glu92, and Glu93, that are essential for the Fd binding and efficient electron transfer to the NR. ITC measurements showed that the most likely stoichiometry for the wild-type NR/wild-type Fd complex is 1:1, a Kd value 4.7 μM for the complex at low ionic strength residues and both the enthalpic and entropic components are associated with complex formation. ITC titrations of wild-type NR with four Fd variants, E29N, D60N, E92Q, and E93N demonstrated that the complex formation, although favorable, was less energetically favorable when compared to complex formation between the two wild-type proteins, suggesting that these negatively charged Fd residues at these positions are important for the effective and productive interaction with wild-type enzyme.
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Affiliation(s)
- Anurag P Srivastava
- Department of Life Sciences, Garden City University, Bangalore, Karnataka, India.
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas, USA.
| | - Neelam Mishra
- Department of Botany, St. Joseph's College, Bangalore, Karnataka, India
| | | | - Preethi Rajesh
- Department of Life Sciences, Garden City University, Bangalore, Karnataka, India.
| | - David B Knaff
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas, USA
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3
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Tan W, Liao TH, Wang J, Ye Y, Wei YC, Zhou HK, Xiao Y, Zhi XY, Shao ZH, Lyu LD, Zhao GP. A recently evolved diflavin-containing monomeric nitrate reductase is responsible for highly efficient bacterial nitrate assimilation. J Biol Chem 2020; 295:5051-5066. [PMID: 32111737 DOI: 10.1074/jbc.ra120.012859] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2020] [Revised: 02/25/2020] [Indexed: 12/11/2022] Open
Abstract
Nitrate is one of the major inorganic nitrogen sources for microbes. Many bacterial and archaeal lineages have the capacity to express assimilatory nitrate reductase (NAS), which catalyzes the rate-limiting reduction of nitrate to nitrite. Although a nitrate assimilatory pathway in mycobacteria has been proposed and validated physiologically and genetically, the putative NAS enzyme has yet to be identified. Here, we report the characterization of a novel NAS encoded by Mycolicibacterium smegmatis Msmeg_4206, designated NasN, which differs from the canonical NASs in its structure, electron transfer mechanism, enzymatic properties, and phylogenetic distribution. Using sequence analysis and biochemical characterization, we found that NasN is an NADPH-dependent, diflavin-containing monomeric enzyme composed of a canonical molybdopterin cofactor-binding catalytic domain and an FMN-FAD/NAD-binding, electron-receiving/transferring domain, making it unique among all previously reported hetero-oligomeric NASs. Genetic studies revealed that NasN is essential for aerobic M. smegmatis growth on nitrate as the sole nitrogen source and that the global transcriptional regulator GlnR regulates nasN expression. Moreover, unlike the NADH-dependent heterodimeric NAS enzyme, NasN efficiently supports bacterial growth under nitrate-limiting conditions, likely due to its significantly greater catalytic activity and oxygen tolerance. Results from a phylogenetic analysis suggested that the nasN gene is more recently evolved than those encoding other NASs and that its distribution is limited mainly to Actinobacteria and Proteobacteria. We observed that among mycobacterial species, most fast-growing environmental mycobacteria carry nasN, but that it is largely lacking in slow-growing pathogenic mycobacteria because of multiple independent genomic deletion events along their evolution.
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Affiliation(s)
- Wei Tan
- Department of Microbiology and Li Ka Shing Institute of Health Sciences, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong 999077, China.,Key Laboratory of Medical Molecular Virology (MOE/NHC/CAMS), School of Basic Medical Sciences and Department of Microbiology and Microbial Engineering, School of Life Sciences, Fudan University, Shanghai 200032, China
| | - Tian-Hua Liao
- Institute of Synthetic Biology, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China
| | - Jin Wang
- College of Life Sciences, Shanghai Normal University, Shanghai 200234, China
| | - Yu Ye
- Department of Microbiology and Li Ka Shing Institute of Health Sciences, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong 999077, China
| | - Yu-Chen Wei
- Department of Microbiology and Li Ka Shing Institute of Health Sciences, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong 999077, China
| | - Hao-Kui Zhou
- Institute of Synthetic Biology, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China
| | - Youli Xiao
- CAS Key Laboratory of Synthetic Biology, CAS Center for Excellence in Molecular Plant Sciences, Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, Shanghai 200032, China
| | - Xiao-Yang Zhi
- Yunnan Institute of Microbiology, School of Life Sciences, Yunnan University, Kunming 650091, China
| | - Zhi-Hui Shao
- CAS Key Laboratory of Synthetic Biology, CAS Center for Excellence in Molecular Plant Sciences, Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, Shanghai 200032, China
| | - Liang-Dong Lyu
- Key Laboratory of Medical Molecular Virology (MOE/NHC/CAMS), School of Basic Medical Sciences and Department of Microbiology and Microbial Engineering, School of Life Sciences, Fudan University, Shanghai 200032, China
| | - Guo-Ping Zhao
- Department of Microbiology and Li Ka Shing Institute of Health Sciences, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong 999077, China .,Key Laboratory of Medical Molecular Virology (MOE/NHC/CAMS), School of Basic Medical Sciences and Department of Microbiology and Microbial Engineering, School of Life Sciences, Fudan University, Shanghai 200032, China.,Institute of Synthetic Biology, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China.,CAS Key Laboratory of Synthetic Biology, CAS Center for Excellence in Molecular Plant Sciences, Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, Shanghai 200032, China.,Bio-Med Big Data Center, Key Laboratory of Computational Biology, CAS-MPG Partner Institute for Computational Biology, Shanghai Institute of Nutrition and Health, Shanghai Institutes for Biological Sciences, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200031, China.,Shanghai-MOST Key Laboratory for Health and Disease Genomics, Chinese National Human Genome Center, Shanghai 201203, China
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4
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Zeamari K, Gerbaud G, Grosse S, Fourmond V, Chaspoul F, Biaso F, Arnoux P, Sabaty M, Pignol D, Guigliarelli B, Burlat B. Tuning the redox properties of a [4Fe-4S] center to modulate the activity of Mo-bisPGD periplasmic nitrate reductase. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2019; 1860:402-413. [DOI: 10.1016/j.bbabio.2019.01.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2018] [Revised: 11/30/2018] [Accepted: 01/25/2019] [Indexed: 11/15/2022]
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5
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Srivastava AP, Hardy EP, Allen JP, Vaccaro BJ, Johnson MK, Knaff DB. Identification of the Ferredoxin-Binding Site of a Ferredoxin-Dependent Cyanobacterial Nitrate Reductase. Biochemistry 2017; 56:5582-5592. [PMID: 28520412 DOI: 10.1021/acs.biochem.7b00025] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
An in silico model for the 1:1 ferredoxin (Fd)/nitrate reductase (NR) complex, using the known structure of Synechocystis sp. PCC 6803 Fd and the in silico model of Synechococcus sp. PCC 7942 NR, is used to map the interaction sites that define the interface between Fd and NR. To test the electrostatic interactions predicted by the model complex, five positively charged NR amino acids (Arg43, Arg46, Arg197, Lys201, and Lys614) and a negatively charged amino acid (Glu219) were altered using site-directed mutagenesis and characterized by activity measurements, metal analysis, and electron paramagnetic resonance (EPR) studies. All of the charge replacement variants retained wild-type levels of activity with reduced methyl viologen (MV), but a significant decrease in activity was observed for the R43Q, R46Q, K201Q, and K614Q variants when reduced Fd served as the electron donor. EPR analysis as well as the Fe and Mo analyses showed that loss of activity observed with these variants was not the consequence of perturbation of the Mo center or [4Fe-4S] cluster. Therefore, the loss of the Fd-linked specific activity observed with these variants can be explained only by invoking a role for Arg43, Arg46, Lys201, and Lys614 in Fd binding. The R43Q, R46Q, K201Q, and K614Q NR variants also showed a decreased binding affinity for Fd, compared to that of wild-type NR, supporting a key role of these four positively charged residues in the productive binding of Fd.
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Affiliation(s)
- Anurag P Srivastava
- Department of Chemistry and Biochemistry, Texas Tech University , Lubbock, Texas 79409-1061, United States
| | - Emily P Hardy
- Department of Chemistry and Biochemistry, Texas Tech University , Lubbock, Texas 79409-1061, United States
| | - James P Allen
- School of Molecular Sciences, Arizona State University , Tempe, Arizona 85287-1604, United States
| | - Brian J Vaccaro
- Department of Chemistry and Center for Metalloenzyme Studies, University of Georgia , Athens, Georgia 30602-2556, United States
| | - Michael K Johnson
- Department of Chemistry and Center for Metalloenzyme Studies, University of Georgia , Athens, Georgia 30602-2556, United States
| | - David B Knaff
- Department of Chemistry and Biochemistry, Texas Tech University , Lubbock, Texas 79409-1061, United States.,Center for Biotechnology and Genomics, Texas Tech University , Lubbock, Texas 79409-3132, United States
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6
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Chu S, Zhang D, Wang D, Zhi Y, Zhou P. Heterologous expression and biochemical characterization of assimilatory nitrate and nitrite reductase reveals adaption and potential of Bacillus megaterium NCT-2 in secondary salinization soil. Int J Biol Macromol 2017; 101:1019-1028. [PMID: 28389402 DOI: 10.1016/j.ijbiomac.2017.04.009] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Revised: 03/30/2017] [Accepted: 04/03/2017] [Indexed: 10/19/2022]
Abstract
Large accumulation of nitrate in soil has resulted in "salt stress" and soil secondary salinization. Bacillus megaterium NCT-2 which was isolated from secondary salinization soil showed high capability of nitrate reduction. The genes encoding assimilatory nitrate and nitrite reductase from NCT-2 were cloned and over-expressed in Escherichia coli. The optimum co-expression condition was obtained with E. coli BL21 (DE3) and 0.1mM IPTG for 10h when expression was carried out at 20°C and 120rpm in Luria-Bertani (LB) medium. The molecular mass of nitrate reductase was 87.3kDa and 80.5kDa for electron transfer and catalytic subunit, respectively. The large and small subunit of nitrite reductase was 88kDa and 11.7kDa, respectively. The purified recombinant enzymes showed broad activity range of temperature and pH. The maximum activities were obtained at 35°C and 30°C, pH 6.2 and 6.5, which was similar to the condition of greenhouse soils. Maximum stimulation of the enzymes occurred with addition of Fe3+, while Cu2+ caused the maximum inhibition. The optimum electron donor was MV+Na2S2O4+EDTA and MV+Na2S2O4, respectively. Kinetic parameters of Km and Vmax were determined to be 670μM and 58U/mg for nitrate reductase, and 3100μM and 5.2U/mg for nitrite reductase. Results of quantitative real-time PCR showed that the maximum expression levels of nitrate and nitrite reductase were obtained at 50mM nitrate for 8h and 12h, respectively. These results provided information on novel assimilatory nitrate and nitrite reductase and their properties presumably revealed adaption of B. megaterium NCT-2 to secondary salinization condition. This study also shed light on the role played by the nitrate assimilatory pathway in B. megaterium NCT-2.
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Affiliation(s)
- Shaohua Chu
- School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, China; Key Laboratory of Urban Agriculture (South), Ministry of Agriculture, Shanghai, China; Bor S. Luh Food Safety Research Center, Shanghai Jiao Tong University, Shanghai, China
| | - Dan Zhang
- School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, China; Key Laboratory of Urban Agriculture (South), Ministry of Agriculture, Shanghai, China; Bor S. Luh Food Safety Research Center, Shanghai Jiao Tong University, Shanghai, China.
| | - Daxin Wang
- School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, China; Key Laboratory of Urban Agriculture (South), Ministry of Agriculture, Shanghai, China; Bor S. Luh Food Safety Research Center, Shanghai Jiao Tong University, Shanghai, China
| | - Yuee Zhi
- School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, China; Key Laboratory of Urban Agriculture (South), Ministry of Agriculture, Shanghai, China; Bor S. Luh Food Safety Research Center, Shanghai Jiao Tong University, Shanghai, China
| | - Pei Zhou
- School of Agriculture and Biology, Shanghai Jiao Tong University, Shanghai, China; Key Laboratory of Urban Agriculture (South), Ministry of Agriculture, Shanghai, China; Bor S. Luh Food Safety Research Center, Shanghai Jiao Tong University, Shanghai, China.
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7
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Kinoshita M, Kim JY, Kume S, Lin Y, Mok KH, Kataoka Y, Ishimori K, Markova N, Kurisu G, Hase T, Lee YH. Energetic basis on interactions between ferredoxin and ferredoxin NADP + reductase at varying physiological conditions. Biochem Biophys Res Commun 2017; 482:909-915. [DOI: 10.1016/j.bbrc.2016.11.132] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Accepted: 11/24/2016] [Indexed: 10/20/2022]
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8
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Non-covalent forces tune the electron transfer complex between ferredoxin and sulfite reductase to optimize enzymatic activity. Biochem J 2016; 473:3837-3854. [PMID: 27551107 DOI: 10.1042/bcj20160658] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2016] [Accepted: 08/22/2016] [Indexed: 11/17/2022]
Abstract
Although electrostatic interactions between negatively charged ferredoxin (Fd) and positively charged sulfite reductase (SiR) have been predominantly highlighted to characterize complex formation, the detailed nature of intermolecular forces remains to be fully elucidated. We investigated interprotein forces for the formation of an electron transfer complex between Fd and SiR and their relationship to SiR activity using various approaches over NaCl concentrations between 0 and 400 mM. Fd-dependent SiR activity assays revealed a bell-shaped activity curve with a maximum ∼40-70 mM NaCl and a reverse bell-shaped dependence of interprotein affinity. Meanwhile, intrinsic SiR activity, as measured in a methyl viologen-dependent assay, exhibited saturation above 100 mM NaCl. Thus, two assays suggested that interprotein interaction is crucial in controlling Fd-dependent SiR activity. Calorimetric analyses showed the monotonic decrease in interprotein affinity on increasing NaCl concentrations, distinguished from a reverse bell-shaped interprotein affinity observed from Fd-dependent SiR activity assay. Furthermore, Fd:SiR complex formation and interprotein affinity were thermodynamically adjusted by both enthalpy and entropy through electrostatic and non-electrostatic interactions. A residue-based NMR investigation on the addition of SiR to 15N-labeled Fd at the various NaCl concentrations also demonstrated that a combination of electrostatic and non-electrostatic forces stabilized the complex with similar interfaces and modulated the binding affinity and mode. Our findings elucidate that non-electrostatic forces are also essential for the formation and modulation of the Fd:SiR complex. We suggest that a complex configuration optimized for maximum enzymatic activity near physiological salt conditions is achieved by structural rearrangement through controlled non-covalent interprotein interactions.
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9
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Srivastava AP, Allen JP, Vaccaro BJ, Hirasawa M, Alkul S, Johnson MK, Knaff DB. Identification of Amino Acids at the Catalytic Site of a Ferredoxin-Dependent Cyanobacterial Nitrate Reductase. Biochemistry 2015; 54:5557-68. [PMID: 26305228 DOI: 10.1021/acs.biochem.5b00511] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
An in silico model of the ferredoxin-dependent nitrate reductase from the cyanobacterium Synechococcus sp. PCC 7942, and information about active sites in related enzymes, had identified Cys148, Met149, Met306, Asp163, and Arg351 as amino acids likely to be involved in either nitrate binding, prosthetic group binding, or catalysis. Site-directed mutagenesis was used to alter each of these residues, and differences in enzyme activity and substrate binding of the purified variants were analyzed. In addition, the effects of these replacements on the assembly and properties of the Mo cofactor and [4Fe-4S] centers were investigated using Mo and Fe determinations, coupled with electron paramagnetic resonance spectroscopy. The C148A, M149A, M306A, D163N, and R351Q variants were all inactive with either the physiological electron donor, reduced ferredoxin, or the nonphysiological electron donor, reduced methyl viologen, as the source of electrons, and all exhibited changes in the properties of the Mo cofactor. Charge-conserving D163E and R351K variants were also inactive, suggesting that specific amino acids are required at these two positions. The implications for the role of these five conserved active-site residues in light of these new results and previous structural, spectroscopic, and mutagenesis studies for related periplasmic nitrate reductases are discussed.
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Affiliation(s)
- Anurag P Srivastava
- Department of Chemistry and Biochemistry, Texas Tech University , Lubbock, Texas 79409-1061, United States
| | - James P Allen
- Department of Chemistry and Biochemistry, Arizona State University , Tempe, Arizona 85287-1604, United States
| | - Brian J Vaccaro
- Department of Chemistry and Center for Metalloenzyme Studies, University of Georgia , Athens, Georgia 30602-2556, United States
| | - Masakazu Hirasawa
- Department of Chemistry and Biochemistry, Texas Tech University , Lubbock, Texas 79409-1061, United States
| | - Suzanne Alkul
- Department of Chemistry and Biochemistry, Texas Tech University , Lubbock, Texas 79409-1061, United States
| | - Michael K Johnson
- Department of Chemistry and Center for Metalloenzyme Studies, University of Georgia , Athens, Georgia 30602-2556, United States
| | - David B Knaff
- Department of Chemistry and Biochemistry, Texas Tech University , Lubbock, Texas 79409-1061, United States.,Center for Biotechnology and Genomics, Texas Tech University , Lubbock, Texas 79409-3132, United States
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10
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Tripathy JN, Hirasawa M, Sutton RB, Dasgupta A, Vaidyanathan N, Zabet-Moghaddam M, Florencio FJ, Srivastava AP, Knaff DB. A loop unique to ferredoxin-dependent glutamate synthases is not absolutely essential for ferredoxin-dependent catalytic activity. PHOTOSYNTHESIS RESEARCH 2015; 123:129-139. [PMID: 25288260 DOI: 10.1007/s11120-014-0044-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2014] [Accepted: 09/22/2014] [Indexed: 06/03/2023]
Abstract
It had been proposed that a loop, typically containing 26 or 27 amino acids, which is only present in monomeric, ferredoxin-dependent, "plant-type" glutamate synthases and is absent from the catalytic α-subunits of both NADPH-dependent, heterodimeric glutamate synthases found in non-photosynthetic bacteria and NADH-dependent heterodimeric cyanobacterial glutamate synthases, plays a key role in productive binding of ferredoxin to the plant-type enzymes. Site-directed mutagenesis has been used to delete the entire 27 amino acid-long loop in the ferredoxin-dependent glutamate synthase from the cyanobacterium Synechocystis sp. PCC 6803. The specific activity of the resulting loopless variant of this glutamate synthase, when reduced ferredoxin serves as the electron donor, is actually higher than that of the wild-type enzyme, suggesting that this loop is not absolutely essential for efficient electron transfer from reduced ferredoxin to the enzyme. These results are consistent with the results of an in-silico study that suggests that the loop is unlikely to interact directly with ferredoxin in the energetically most favorable model of a 1:1 complex of ferredoxin with the wild-type enzyme.
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Affiliation(s)
- Jatindra N Tripathy
- Center for Biotechnology and Genomics, Texas Tech University, Lubbock, TX, 79409-3132, USA
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Electron-transfer kinetics in cyanobacterial cells: methyl viologen is a poor inhibitor of linear electron flow. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2014; 1847:212-222. [PMID: 25448535 DOI: 10.1016/j.bbabio.2014.10.008] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 09/18/2014] [Revised: 10/24/2014] [Accepted: 10/28/2014] [Indexed: 01/13/2023]
Abstract
The inhibitor methyl viologen (MV) has been widely used in photosynthesis to study oxidative stress. Its effects on electron transfer kinetics in Synechocystis sp. PCC6803 cells were studied to characterize its electron-accepting properties. For the first hundreds of flashes following MV addition at submillimolar concentrations, the kinetics of NADPH formation were hardly modified (less than 15% decrease in signal amplitude) with a significant signal decrease only observed after more flashes or continuous illumination. The dependence of the P700 photooxidation kinetics on the MV concentration exhibited a saturation effect at 0.3 mM MV, a concentration which inhibits the recombination reactions in photosystem I. The kinetics of NADPH formation and decay under continuous light with MV at 0.3 mM showed that MV induces the oxidation of the NADP pool in darkness and that the yield of linear electron transfer decreased by only 50% after 1.5-2 photosystem-I turnovers. The unexpectedly poor efficiency of MV in inhibiting NADPH formation was corroborated by in vitro flash-induced absorption experiments with purified photosystem-I, ferredoxin and ferredoxin-NADP(+)-oxidoreductase. These experiments showed that the second-order rate constants of MV reduction are 20 to 40-fold smaller than the competing rate constants involved in reduction of ferredoxin and ferredoxin-NADP(+)-oxidoreductase. The present study shows that MV, which accepts electrons in vivo both at the level of photosystem-I and ferredoxin, can be used at submillimolar concentrations to inhibit recombination reactions in photosystem-I with only a moderate decrease in the efficiency of fast reactions involved in linear electron transfer and possibly cyclic electron transfer.
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12
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Srivastava AP, Knaff DB, Sétif P. Kinetic Studies of a Ferredoxin-Dependent Cyanobacterial Nitrate Reductase. Biochemistry 2014; 53:5092-101. [DOI: 10.1021/bi500386n] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Anurag P. Srivastava
- Department
of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061, United States
| | - David B. Knaff
- Department
of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061, United States
- Center
for Biotechnology and Genomics, Texas Tech University, Lubbock, Texas 79409-3132, United States
| | - Pierre Sétif
- iBiTec-S, CNRS UMR 8221,
CEA Saclay, 91191 Gif-sur-Yvette, France
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13
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Affiliation(s)
- Russ Hille
- Department of Biochemistry, University of California, Riverside, Riverside, California 92521, United States
| | - James Hall
- Department of Biochemistry, University of California, Riverside, Riverside, California 92521, United States
| | - Partha Basu
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282, United States
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