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Zhou J, Deng W, Wu J, Xiang H, Shen X, Lin JG, Hong Y. Respiration and growth of Paracoccus denitrificans R-1 with nitrous oxide as an electron acceptor. Microbiol Spectr 2024; 12:e0381123. [PMID: 38647341 DOI: 10.1128/spectrum.03811-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2023] [Accepted: 03/22/2024] [Indexed: 04/25/2024] Open
Abstract
In the nitrogen biogeochemical cycle, the reduction of nitrous oxide (N2O) to N2 by N2O reductase, which is encoded by nosZ gene, is the only biological pathway for N2O consumption. In this study, we successfully isolated a strain of denitrifying Paracoccus denitrificans R-1 from sewage treatment plant sludge. This strain has strong N2O reduction capability, and the average N2O reduction rate was 5.10 ± 0.11 × 10-9 µmol·h-1·cell-1 under anaerobic condition in a defined medium. This reduction was accompanied by the stoichiometric consumption of acetate over time when N2O served as the sole electron acceptor and the reduction can yield energy to support microbial growth, suggesting that microbial N2O reduction is related to the energy generation process. Genomic analysis showed that the gene cluster encoding N2O reductase of P. denitrificans R-1 was composed of nosR, nosZ, nosD, nosF, nosY, nosL, and nosZ, which was identified as that in other strains in clade I. Respiratory inhibitors test indicated that the pathway of electron transport for N2O reduction was different from that of the traditional electron transport chain for aerobic respiration. Cu2+, silver nanoparticles, O2, and acidic conditions can strongly inhibit the reduction, whereas NO3- or NH4+ can promote it. These findings suggest that modular N2O reduction of P. denitrificans R-1 is linked to the electron transport and energy conservation, and dissimilatory N2O reduction is a form of microbial anaerobic respiration. IMPORTANCE Nitrous oxide (N2O) is a potent greenhouse gas and contributor to ozone layer destruction, and atmospheric N2O has increased steadily over the past century due to human activities. The release of N2O from fixed N is almost entirely controlled by microbial N2O reductase activities. Here, we investigated the ability to obtain energy for the growth of Paracoccus denitrificans R-1 by coupling the oxidation of various electron donors to N2O reduction. The modular N2O reduction process of denitrifying microorganism not only can consume N2O produced by itself but also can consume the external N2O generated from biological or abiotic pathways under suitable condition, which should be critical for controlling the release of N2O from ecosystems into the atmosphere.
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Affiliation(s)
- Jiaxian Zhou
- Institute of Environmental Research at Greater Bay Area; Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, Guangzhou University, Guangzhou, China
- School of Environmental Science and Engineering, Guangzhou University, Guangzhou, China
| | - Wenfang Deng
- Institute of Environmental Research at Greater Bay Area; Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, Guangzhou University, Guangzhou, China
| | - Jiapeng Wu
- Institute of Environmental Research at Greater Bay Area; Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, Guangzhou University, Guangzhou, China
| | - Hua Xiang
- Institute of Environmental Research at Greater Bay Area; Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, Guangzhou University, Guangzhou, China
| | - Xiaomei Shen
- Institute of Environmental Research at Greater Bay Area; Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, Guangzhou University, Guangzhou, China
| | - Jih-Gaw Lin
- Institute of Environmental Engineering, National Yangming Chiao Tung University, Hsinchu City, Taiwan
| | - Yiguo Hong
- Institute of Environmental Research at Greater Bay Area; Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of Education, Guangzhou University, Guangzhou, China
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Plant-Pathogenic Ralstonia Phylotypes Evolved Divergent Respiratory Strategies and Behaviors To Thrive in Xylem. mBio 2023; 14:e0318822. [PMID: 36744950 PMCID: PMC9973335 DOI: 10.1128/mbio.03188-22] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Bacterial pathogens in the Ralstonia solanacearum species complex (RSSC) infect the water-transporting xylem vessels of plants, causing bacterial wilt disease. Strains in RSSC phylotypes I and III can reduce nitrate to dinitrogen via complete denitrification. The four-step denitrification pathway enables bacteria to use inorganic nitrogen species as terminal electron acceptors, supporting their growth in oxygen-limited environments such as biofilms or plant xylem. Reduction of nitrate, nitrite, and nitric oxide all contribute to the virulence of a model phylotype I strain. However, little is known about the physiological role of the last denitrification step, the reduction of nitrous oxide to dinitrogen by NosZ. We found that phylotypes I and III need NosZ for full virulence. However, strains in phylotypes II and IV are highly virulent despite lacking NosZ. The ability to respire by reducing nitrate to nitrous oxide does not greatly enhance the growth of phylotype II and IV strains. These partial denitrifying strains reach high cell densities during plant infection and cause typical wilt disease. However, unlike phylotype I and III strains, partial denitrifiers cannot grow well under anaerobic conditions or form thick biofilms in culture or in tomato xylem vessels. Furthermore, aerotaxis assays show that strains from different phylotypes have different oxygen and nitrate preferences. Together, these results indicate that the RSSC contains two subgroups that occupy the same habitat but have evolved divergent energy metabolism strategies to exploit distinct metabolic niches in the xylem. IMPORTANCE Plant-pathogenic Ralstonia spp. are a heterogeneous globally distributed group of bacteria that colonize plant xylem vessels. Ralstonia cells multiply rapidly in plants and obstruct water transport, causing fatal wilting and serious economic losses of many key food security crops. The virulence of these pathogens depends on their ability to grow to high cell densities in the low-oxygen xylem environment. Plant-pathogenic Ralstonia can use denitrifying respiration to generate ATP. The last denitrification step, nitrous oxide reduction by NosZ, contributes to energy production and virulence for only one of the three phytopathogenic Ralstonia species. These complete denitrifiers form thicker biofilms in culture and in tomato xylem, suggesting they are better adapted to hypoxic niches. Strains with partial denitrification physiology form less biofilm and are more often planktonic. They are nonetheless highly virulent. Thus, these closely related bacteria have adapted their core metabolic functions to exploit distinct microniches in the same habitat.
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Pacheco PJ, Cabrera JJ, Jiménez-Leiva A, Bedmar EJ, Mesa S, Tortosa G, Delgado MJ. Effect of Copper on Expression of Functional Genes and Proteins Associated with Bradyrhizobium diazoefficiens Denitrification. Int J Mol Sci 2022; 23:ijms23063386. [PMID: 35328804 PMCID: PMC8951191 DOI: 10.3390/ijms23063386] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Revised: 03/16/2022] [Accepted: 03/17/2022] [Indexed: 12/16/2022] Open
Abstract
Nitrous oxide (N2O) is a powerful greenhouse gas that contributes to climate change. Denitrification is one of the largest sources of N2O in soils. The soybean endosymbiont Bradyrhizobium diazoefficiens is a model for rhizobial denitrification studies since, in addition to fixing N2, it has the ability to grow anaerobically under free-living conditions by reducing nitrate from the medium through the complete denitrification pathway. This bacterium contains a periplasmic nitrate reductase (Nap), a copper (Cu)-containing nitrite reductase (NirK), a c-type nitric oxide reductase (cNor), and a Cu-dependent nitrous oxide reductase (Nos) encoded by the napEDABC, nirK, norCBQD and nosRZDFYLX genes, respectively. In this work, an integrated study of the role of Cu in B. diazoefficiens denitrification has been performed. A notable reduction in nirK, nor, and nos gene expression observed under Cu limitation was correlated with a significant decrease in NirK, NorC and NosZ protein levels and activities. Meanwhile, nap expression was not affected by Cu, but a remarkable depletion in Nap activity was found, presumably due to an inhibitory effect of nitrite accumulated under Cu-limiting conditions. Interestingly, a post-transcriptional regulation by increasing Nap and NirK activities, as well as NorC and NosZ protein levels, was observed in response to high Cu. Our results demonstrate, for the first time, the role of Cu in transcriptional and post-transcriptional control of B. diazoefficiens denitrification. Thus, this study will contribute by proposing useful strategies for reducing N2O emissions from agricultural soils.
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Bennett SP, Torres MJ, Soriano-Laguna MJ, Richardson DJ, Gates AJ, Le Brun NE. nosX is essential for whole-cell N 2O reduction in Paracoccus denitrificans but not for assembly of copper centres of nitrous oxide reductase. MICROBIOLOGY-SGM 2020; 166:909-917. [PMID: 32886603 PMCID: PMC7660919 DOI: 10.1099/mic.0.000955] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Nitrous oxide (N2O) is a potent greenhouse gas that is produced naturally as an intermediate during the process of denitrification carried out by some soil bacteria. It is consumed by nitrous oxide reductase (N2OR), the terminal enzyme of the denitrification pathway, which catalyses a reduction reaction to generate dinitrogen. N2OR contains two important copper cofactors (CuA and CuZ centres) that are essential for activity, and in copper-limited environments, N2OR fails to function, contributing to rising levels of atmospheric N2O and a major environmental challenge. Here we report studies of nosX, one of eight genes in the nos cluster of the soil dwelling α-proteobaterium Paraccocus denitrificans. A P. denitrificans ΔnosX deletion mutant failed to reduce N2O under both copper-sufficient and copper-limited conditions, demonstrating that NosX plays an essential role in N2OR activity. N2OR isolated from nosX-deficient cells was found to be unaffected in terms of the assembly of its copper cofactors, and to be active in in vitro assays, indicating that NosX is not required for the maturation of the enzyme; in particular, it plays no part in the assembly of either of the CuA and CuZ centres. Furthermore, quantitative Reverse Transcription PCR (qRT-PCR) studies showed that NosX does not significantly affect the expression of the N2OR-encoding nosZ gene. NosX is a homologue of the FAD-binding protein ApbE from Pseudomonas stutzeri, which functions in the flavinylation of another N2OR accessory protein, NosR. Thus, it is likely that NosX is a system-specific maturation factor of NosR, and so is indirectly involved in maintaining the reaction cycle of N2OR and cellular N2O reduction.
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Affiliation(s)
- Sophie P Bennett
- Centre for Molecular and Structural Biochemistry, School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK
| | - Maria J Torres
- Centre for Molecular and Structural Biochemistry, School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK
| | - Manuel J Soriano-Laguna
- Centre for Molecular and Structural Biochemistry, School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK
| | - David J Richardson
- Centre for Molecular and Structural Biochemistry, School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK
| | - Andrew J Gates
- Centre for Molecular and Structural Biochemistry, School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK
| | - Nick E Le Brun
- Centre for Molecular and Structural Biochemistry, School of Chemistry, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK
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Carreira C, Nunes RF, Mestre O, Moura I, Pauleta SR. The effect of pH on Marinobacter hydrocarbonoclasticus denitrification pathway and nitrous oxide reductase. J Biol Inorg Chem 2020; 25:927-940. [PMID: 32851479 DOI: 10.1007/s00775-020-01812-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2020] [Accepted: 08/12/2020] [Indexed: 11/27/2022]
Abstract
Increasing atmospheric concentration of N2O has been a concern, as it is a potent greenhouse gas and promotes ozone layer destruction. In the N-cycle, release of N2O is boosted upon a drop of pH in the environment. Here, Marinobacter hydrocarbonoclasticus was grown in batch mode in the presence of nitrate, to study the effect of pH in the denitrification pathway by gene expression profiling, quantification of nitrate and nitrite, and evaluating the ability of whole cells to reduce NO and N2O. At pH 6.5, accumulation of nitrite in the medium occurs and the cells were unable to reduce N2O. In addition, the biochemical properties of N2O reductase isolated from cells grown at pH 6.5, 7.5 and 8.5 were compared for the first time. The amount of this enzyme at acidic pH was lower than that at pH 7.5 and 8.5, pinpointing to a post-transcriptional regulation, though pH did not affect gene expression of N2O reductase accessory genes. N2O reductase isolated from cells grown at pH 6.5 has its catalytic center mainly as CuZ(4Cu1S), while that from cells grown at pH 7.5 or 8.5 has it as CuZ(4Cu2S). This study evidences that an in vivo secondary level of regulation is required to maintain N2O reductase in an active state.
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Affiliation(s)
- Cíntia Carreira
- Microbial Stress Lab, UCIBIO, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516, Caparica, Portugal
- Biological Chemistry Lab, LAQV, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516, Caparica, Portugal
| | - Rute F Nunes
- Microbial Stress Lab, UCIBIO, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516, Caparica, Portugal
| | - Olga Mestre
- Microbial Stress Lab, UCIBIO, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516, Caparica, Portugal
| | - Isabel Moura
- Biological Chemistry Lab, LAQV, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516, Caparica, Portugal
| | - Sofia R Pauleta
- Microbial Stress Lab, UCIBIO, REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516, Caparica, Portugal.
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Bacterial nitrous oxide respiration: electron transport chains and copper transfer reactions. Adv Microb Physiol 2019; 75:137-175. [PMID: 31655736 DOI: 10.1016/bs.ampbs.2019.07.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Biologically catalyzed nitrous oxide (N2O, laughing gas) reduction to dinitrogen gas (N2) is a desirable process in the light of ever-increasing atmospheric concentrations of this important greenhouse gas and ozone depleting substance. A diverse range of bacterial species produce the copper cluster-containing enzyme N2O reductase (NosZ), which is the only known enzyme that converts N2O to N2. Based on phylogenetic analyses, NosZ enzymes have been classified into clade I or clade II and it has turned out that this differentiation is also applicable to nos gene clusters (NGCs) and some physiological traits of the corresponding microbial cells. The NosZ enzyme is the terminal reductase of anaerobic N2O respiration, in which electrons derived from a donor substrate are transferred to NosZ by means of an electron transport chain (ETC) that conserves energy through proton motive force generation. This chapter presents models of the ETCs involved in clade I and clade II N2O respiration as well as of the respective NosZ maturation and maintenance processes. Despite differences in NGCs and growth yields of N2O-respiring microorganisms, the deduced bioenergetic framework in clade I and clade II N2O respiration is assumed to be equivalent. In both cases proton motive quinol oxidation by N2O is thought to be catalyzed by the Q cycle mechanism of a membrane-bound Rieske/cytochrome bc complex. However, clade I and clade II organisms are expected to differ significantly in terms of auxiliary electron transport processes as well as NosZ active site maintenance and repair.
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Li W, Li H, Liu YD, Zheng P, Shapleigh JP. Salinity-Aided Selection of Progressive Onset Denitrifiers as a Means of Providing Nitrite for Anammox. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2018; 52:10665-10672. [PMID: 30148965 DOI: 10.1021/acs.est.8b02314] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Anaerobic ammonium oxidation (anammox) combined with partial-denitrification (NO3- → NO2-) is an innovative process for the simultaneous removal of ammonia and nitrate from wastewaters. An efficient method for the selection of partial denitrifying community, which relies on increasing influent salinity, is described. Using this method, a denitratating community was enriched, which showed a nitrite accumulation efficiency higher than 75% as well as a high nitrate conversion efficiency. Community analysis using 16S rDNA indicated that Halomonas became the dominant genus as salinity increased. Metagenomic analysis revealed that there was not a significant difference in reads mapping to downstream denitrification genes in a comparison of samples from cultures with 5% salinity to those without salinity. The majority of the reads mapping to the genes encoding dissimilatory nitrate and nitrite reductases nar and nirS came from Halomonas under high salinity conditions. Two metagenome-assembled genomes taxonomically assigned to Halomonas were obtained, one of which accounted for ∼35% of the reads under high salinity conditions. Both genomes harbored the genes for the complete denitrification pathway. These results indicate progressive onset denitrifiers, a phenotype where nitrite reduction only occurs after nitrate exhaustion, could be successfully enriched with increasing salinity. Progressive onset denitrifiers may be more widespread in natural and artificial habitats than anticipated and are shown here to be valuable for nitrogen mitigating processes.
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Affiliation(s)
- Wei Li
- National Engineering Laboratory for Industrial Wastewater Treatment, School of Resources and Environmental Engineering , East China University of Science and Technology , Shanghai 200237 , China
- Department of Environmental Engineering, College of Environmental and Resource Science , Zhejiang University , Hangzhou 310027 , China
- Department of Microbiology , Cornell University , Ithaca , New York 14850 , United States
- Shanghai Institute of Pollution Control and Ecological Security , Shanghai 200092 , China
| | - Hui Li
- National Engineering Laboratory for Industrial Wastewater Treatment, School of Resources and Environmental Engineering , East China University of Science and Technology , Shanghai 200237 , China
| | - Yong-di Liu
- National Engineering Laboratory for Industrial Wastewater Treatment, School of Resources and Environmental Engineering , East China University of Science and Technology , Shanghai 200237 , China
| | - Ping Zheng
- Department of Environmental Engineering, College of Environmental and Resource Science , Zhejiang University , Hangzhou 310027 , China
| | - James P Shapleigh
- Department of Microbiology , Cornell University , Ithaca , New York 14850 , United States
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The catalytic cycle of nitrous oxide reductase - The enzyme that catalyzes the last step of denitrification. J Inorg Biochem 2017; 177:423-434. [PMID: 28927704 DOI: 10.1016/j.jinorgbio.2017.09.007] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2017] [Revised: 09/02/2017] [Accepted: 09/08/2017] [Indexed: 01/27/2023]
Abstract
The reduction of the potent greenhouse gas nitrous oxide requires a catalyst to overcome the large activation energy barrier of this reaction. Its biological decomposition to the inert dinitrogen can be accomplished by denitrifiers through nitrous oxide reductase, the enzyme that catalyzes the last step of the denitrification, a pathway of the biogeochemical nitrogen cycle. Nitrous oxide reductase is a multicopper enzyme containing a mixed valence CuA center that can accept electrons from small electron shuttle proteins, triggering electron flow to the catalytic sulfide-bridged tetranuclear copper "CuZ center". This enzyme has been isolated with its catalytic center in two forms, CuZ*(4Cu1S) and CuZ(4Cu2S), proven to be spectroscopic and structurally different. In the last decades, it has been a challenge to characterize the properties of this complex enzyme, due to the different oxidation states observed for each of its centers and the heterogeneity of its preparations. The substrate binding site in those two "CuZ center" forms and which is the active form of the enzyme is still a matter of debate. However, in the last years the application of different spectroscopies, together with theoretical calculations have been useful in answering these questions and in identifying intermediate species of the catalytic cycle. An overview of the spectroscopic, kinetics and structural properties of the two forms of the catalytic "CuZ center" is given here, together with the current knowledge on nitrous oxide reduction mechanism by nitrous oxide reductase and its intermediate species.
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Phenotypic and genotypic richness of denitrifiers revealed by a novel isolation strategy. ISME JOURNAL 2017; 11:2219-2232. [PMID: 28696424 DOI: 10.1038/ismej.2017.82] [Citation(s) in RCA: 90] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Revised: 04/21/2017] [Accepted: 04/24/2017] [Indexed: 11/08/2022]
Abstract
Present-day knowledge on the regulatory biology of denitrification is based on studies of selected model organisms. These show large variations in their potential contribution to NO2-, NO, and N2O accumulation, attributed to lack of genes coding for denitrification reductases, but also to variations in their transcriptional regulation, as well as to post-transcriptional phenomena. To validate the relevance of these observations, there is a need to study a wider range of denitrifiers. We designed an isolation protocol that identifies all possible combinations of truncated denitrification chains (NO3-/NO2-/NO/N2O/N2). Of 176 isolates from two soils (pH 3.7 and 7.4), 30 were denitrifiers sensu stricto, reducing NO2- to gas, and five capable of N2O reduction only. Altogether, 70 isolates performed at least one reduction step, including two DNRA isolates. Gas kinetics and electron flow calculations revealed that several features with potential impact on N2O production, reported from model organisms, also exist in these novel isolates, including denitrification bet-hedging and control of NO2-/NO/N2O accumulation. Whole genome sequencing confirmed most truncations but also showed that phenotypes cannot be predicted solely from genetic potential. Interestingly, and opposed to the commonly observed inability to reduce N2O under acidic conditions, one isolate identified as Rhodanobacter reduced N2O only at low pH.
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Zhang L, Trncik C, Andrade SLA, Einsle O. The flavinyl transferase ApbE of Pseudomonas stutzeri matures the NosR protein required for nitrous oxide reduction. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2016; 1858:95-102. [PMID: 27864152 DOI: 10.1016/j.bbabio.2016.11.008] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2016] [Revised: 11/09/2016] [Accepted: 11/11/2016] [Indexed: 12/15/2022]
Abstract
The copper-containing enzyme nitrous oxide reductase (N2OR) catalyzes the transformation of nitrous oxide (N2O) to dinitrogen (N2) in microbial denitrification. Several accessory factors are essential for assembling the two copper sites CuA and CuZ, and for maintaining the activity. In particular, the deletion of either the transmembrane iron-sulfur flavoprotein NosR or the periplasmic protein NosX, a member of the ApbE family, abolishes N2O respiration. Here we demonstrate through biochemical and structural studies that the ApbE protein from Pseudomonas stutzeri, where the nosX gene is absent, is a monomeric FAD-binding protein that can serve as the flavin donor for NosR maturation via covalent flavinylation of a threonine residue. The flavin transfer reaction proceeds both in vivo and in vitro to generate post-translationally modified NosR with covalently bound FMN. Only FAD can act as substrate and the reaction requires a divalent cation, preferably Mg2+ that was also present in the crystal structure. In addition, the reaction is species-specific to a certain extent.
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Affiliation(s)
- Lin Zhang
- Institute for Biochemistry, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg im Breisgau, Germany
| | - Christian Trncik
- Institute for Biochemistry, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg im Breisgau, Germany
| | - Susana L A Andrade
- Institute for Biochemistry, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg im Breisgau, Germany; BIOSS Centre for Biological Signalling Studies, Schänzlestrasse 1, 79104 Freiburg im Breisgau, Germany
| | - Oliver Einsle
- Institute for Biochemistry, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg im Breisgau, Germany; BIOSS Centre for Biological Signalling Studies, Schänzlestrasse 1, 79104 Freiburg im Breisgau, Germany.
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Torres M, Simon J, Rowley G, Bedmar E, Richardson D, Gates A, Delgado M. Nitrous Oxide Metabolism in Nitrate-Reducing Bacteria: Physiology and Regulatory Mechanisms. Adv Microb Physiol 2016; 68:353-432. [PMID: 27134026 DOI: 10.1016/bs.ampbs.2016.02.007] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Nitrous oxide (N2O) is an important greenhouse gas (GHG) with substantial global warming potential and also contributes to ozone depletion through photochemical nitric oxide (NO) production in the stratosphere. The negative effects of N2O on climate and stratospheric ozone make N2O mitigation an international challenge. More than 60% of global N2O emissions are emitted from agricultural soils mainly due to the application of synthetic nitrogen-containing fertilizers. Thus, mitigation strategies must be developed which increase (or at least do not negatively impact) on agricultural efficiency whilst decrease the levels of N2O released. This aim is particularly important in the context of the ever expanding population and subsequent increased burden on the food chain. More than two-thirds of N2O emissions from soils can be attributed to bacterial and fungal denitrification and nitrification processes. In ammonia-oxidizing bacteria, N2O is formed through the oxidation of hydroxylamine to nitrite. In denitrifiers, nitrate is reduced to N2 via nitrite, NO and N2O production. In addition to denitrification, respiratory nitrate ammonification (also termed dissimilatory nitrate reduction to ammonium) is another important nitrate-reducing mechanism in soil, responsible for the loss of nitrate and production of N2O from reduction of NO that is formed as a by-product of the reduction process. This review will synthesize our current understanding of the environmental, regulatory and biochemical control of N2O emissions by nitrate-reducing bacteria and point to new solutions for agricultural GHG mitigation.
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Johnston EM, Dell'Acqua S, Pauleta SR, Moura I, Solomon EI. Protonation state of the Cu 4S 2 Cu Z site in nitrous oxide reductase: redox dependence and insight into reactivity. Chem Sci 2015; 6:5670-5679. [PMID: 26417423 PMCID: PMC4583207 DOI: 10.1039/c5sc02102b] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2015] [Accepted: 07/03/2015] [Indexed: 11/21/2022] Open
Abstract
Spectroscopic and computational methods have been used to determine the protonation state of the edge sulfur ligand in the Cu4S2 CuZ form of the active site of nitrous oxide reductase (N2OR) in its 3CuICuII (1-hole) and 2CuI2CuII (2-hole) redox states. The EPR, absorption, and MCD spectra of 1-hole CuZ indicate that the unpaired spin in this site is evenly delocalized over CuI, CuII, and CuIV. 1-hole CuZ is shown to have a μ2-thiolate edge ligand from the observation of S-H bending modes in the resonance Raman spectrum at 450 and 492 cm-1 that have significant deuterium isotope shifts (-137 cm-1) and are not perturbed up to pH 10. 2-hole CuZ is characterized with absorption and resonance Raman spectroscopies as having two Cu-S stretching vibrations that profile differently. DFT models of the 1-hole and 2-hole CuZ sites are correlated to these spectroscopic features to determine that 2-hole CuZ has a μ2-sulfide edge ligand at neutral pH. The slow two electron (+1 proton) reduction of N2O by 1-hole CuZ is discussed and the possibility of a reaction between 2-hole CuZ and O2 is considered.
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Affiliation(s)
- Esther M. Johnston
- Department of Chemistry , Stanford University , Stanford , CA 94305 , USA .
| | - Simone Dell'Acqua
- Dipartimento di Chimica , Università di Pavia , Via Taramelli 12 , 27100 Pavia , Italy
| | - Sofia R. Pauleta
- UCIBIO , REQUIMTE , Departamento de Química , Faculdade de Ciências e Tecnologia , Universidade Nova de Lisboa , 2829-516 Caparica , Portugal
| | - Isabel Moura
- UCIBIO , REQUIMTE , Departamento de Química , Faculdade de Ciências e Tecnologia , Universidade Nova de Lisboa , 2829-516 Caparica , Portugal
| | - Edward I. Solomon
- Department of Chemistry , Stanford University , Stanford , CA 94305 , USA .
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Solomon EI, Heppner DE, Johnston EM, Ginsbach JW, Cirera J, Qayyum M, Kieber-Emmons MT, Kjaergaard CH, Hadt RG, Tian L. Copper active sites in biology. Chem Rev 2014; 114:3659-853. [PMID: 24588098 PMCID: PMC4040215 DOI: 10.1021/cr400327t] [Citation(s) in RCA: 1112] [Impact Index Per Article: 111.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
| | - David E. Heppner
- Department of Chemistry, Stanford University, Stanford, CA, 94305
| | | | - Jake W. Ginsbach
- Department of Chemistry, Stanford University, Stanford, CA, 94305
| | - Jordi Cirera
- Department of Chemistry, Stanford University, Stanford, CA, 94305
| | - Munzarin Qayyum
- Department of Chemistry, Stanford University, Stanford, CA, 94305
| | | | | | - Ryan G. Hadt
- Department of Chemistry, Stanford University, Stanford, CA, 94305
| | - Li Tian
- Department of Chemistry, Stanford University, Stanford, CA, 94305
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No laughing matter: the unmaking of the greenhouse gas dinitrogen monoxide by nitrous oxide reductase. Met Ions Life Sci 2014; 14:177-210. [PMID: 25416395 DOI: 10.1007/978-94-017-9269-1_8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The gas nitrous oxide (N₂O) is generated in a variety of abiotic, biotic, and anthropogenic processes and it has recently been under scrutiny for its role as a greenhouse gas. A single enzyme, nitrous oxide reductase, is known to reduce N₂O to uncritical N₂, in a two-electron reduction process that is catalyzed at two unusual metal centers containing copper. Nitrous oxide reductase is a bacterial metalloprotein from the metabolic pathway of denitrification, and it forms a 130 kDa homodimer in which the two metal sites CuA and CuZ from opposing monomers are brought into close contact to form the active site of the enzyme. CuA is a binuclear, valence-delocalized cluster that accepts and transfers a single electron. The CuA site of nitrous oxide reductase is highly similar to that of respiratory heme-copper oxidases, but in the denitrification enzyme the site additionally undergoes a conformational change on a ligand that is suggested to function as a gate for electron transfer from an external donor protein. CuZ, the tetranuclear active center of nitrous oxide reductase, is isolated under mild and anoxic conditions as a unique [4Cu:2S] cluster. It is easily desulfurylated to yield a [4Cu:S] state termed CuZ (*) that is functionally distinct. The CuZ form of the cluster is catalytically active, while CuZ (*) is inactive as isolated in the [3Cu(1+):1Cu(2+)] state. However, only CuZ (*) can be reduced to an all-cuprous state by sodium dithionite, yielding a form that shows higher activities than CuZ. As the possibility of a similar reductive activation in the periplasm is unconfirmed, the mechanism and the actual functional state of the enzyme remain under debate. Using enzyme from anoxic preparations with CuZ in the [4Cu:2S] state, N2O was shown to bind between the CuA and CuZ sites, suggesting direct electron transfer from CuA to the substrate after its activation by CuZ.
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Dell'Acqua S, Pauleta SR, Moura JJG, Moura I. Biochemical characterization of the purple form of Marinobacter hydrocarbonoclasticus nitrous oxide reductase. Philos Trans R Soc Lond B Biol Sci 2012; 367:1204-12. [PMID: 22451106 DOI: 10.1098/rstb.2011.0311] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Nitrous oxide reductase (N(2)OR) catalyses the final step of the denitrification pathway-the reduction of nitrous oxide to nitrogen. The catalytic centre (CuZ) is a unique tetranuclear copper centre bridged by inorganic sulphur in a tetrahedron arrangement that can have different oxidation states. Previously, Marinobacter hydrocarbonoclasticus N(2)OR was isolated with the CuZ centre as CuZ*, in the [1Cu(2+) : 3Cu(+)] redox state, which is redox inert and requires prolonged incubation under reductive conditions to be activated. In this work, we report, for the first time, the isolation of N(2)OR from M. hydrocarbonoclasticus in the 'purple' form, in which the CuZ centre is in the oxidized [2Cu(2+) : 2Cu(+)] redox state and is redox active. This form of the enzyme was isolated in the presence of oxygen from a microaerobic culture in the presence of nitrate and also from a strictly anaerobic culture. The purple form of the enzyme was biochemically characterized and was shown to be a redox active species, although it is still catalytically non-competent, as its specific activity is lower than that of the activated fully reduced enzyme and comparable with that of the enzyme with the CuZ centre in either the [1Cu(2+) : 3Cu(+)] redox state or in the redox inactive CuZ* state.
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Affiliation(s)
- Simone Dell'Acqua
- REQUIMTE/CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal
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18
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Bergaust L, van Spanning RJM, Frostegård Å, Bakken LR. Expression of nitrous oxide reductase in Paracoccus denitrificans is regulated by oxygen and nitric oxide through FnrP and NNR. MICROBIOLOGY-SGM 2011; 158:826-834. [PMID: 22174385 PMCID: PMC3541799 DOI: 10.1099/mic.0.054148-0] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The reductases performing the four steps of denitrification are controlled by a network of transcriptional regulators and ancillary factors responding to intra- and extracellular signals, amongst which are oxygen and N oxides (NO and NO2–). Although many components of the regulatory network have been identified, there are gaps in our understanding of their role(s) in controlling the expression of the various reductases, in particular the environmentally important N2O reductase (N2OR). We investigated denitrification phenotypes of Paracoccus denitrificans mutants deficient in: (i) regulatory proteins (three FNR-type transcriptional regulators, NarR, NNR and FnrP, and NirI, which is involved in transcription activation of the structural nir cluster); (ii) functional enzymes (NO reductase and N2OR); or (iii) ancillary factors involved in N2O reduction (NirX and NosX). A robotized incubation system allowed us to closely monitor changes in concentrations of oxygen and all gaseous products during the transition from oxic to anoxic respiration. Strains deficient in NO reductase were able to grow during denitrification, despite reaching micromolar concentrations of NO, but were unable to return to oxic respiration. The FnrP mutant showed linear anoxic growth in a medium with nitrate as the sole NOx, but exponential growth was restored by replacing nitrate with nitrite. We interpret this as nitrite limitation, suggesting dual transcriptional control of respiratory nitrate reductase (NAR) by FnrP and NarR. Mutations in either NirX or NosX did not affect the phenotype, but the double mutant lacked the potential to reduce N2O. Finally, we found that FnrP and NNR are alternative and equally effective inducers of N2OR.
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Affiliation(s)
- Linda Bergaust
- Department of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences, Ås, Norway
- Department of Plant and Environmental Sciences, Norwegian University of Life Sciences, Ås, Norway
| | - Rob J. M. van Spanning
- Department of Molecular Cell Biology, Faculty of Earth and Life Science, VU University, Amsterdam, The Netherlands
| | - Åsa Frostegård
- Department of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences, Ås, Norway
| | - Lars R. Bakken
- Department of Plant and Environmental Sciences, Norwegian University of Life Sciences, Ås, Norway
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Dell'Acqua S, Pauleta SR, Moura I, Moura JJG. The tetranuclear copper active site of nitrous oxide reductase: the CuZ center. J Biol Inorg Chem 2011; 16:183-94. [PMID: 21240533 DOI: 10.1007/s00775-011-0753-3] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2010] [Accepted: 01/03/2011] [Indexed: 01/24/2023]
Abstract
This review focuses on the novel CuZ center of nitrous oxide reductase, an important enzyme owing to the environmental significance of the reaction it catalyzes, reduction of nitrous oxide, and the unusual nature of its catalytic center, named CuZ. The structure of the CuZ center, the unique tetranuclear copper center found in this enzyme, opened a novel area of research in metallobiochemistry. In the last decade, there has been progress in defining the structure of the CuZ center, characterizing the mechanism of nitrous oxide reduction, and identifying intermediates of this reaction. In addition, the determination of the structure of the CuZ center allowed a structural interpretation of the spectroscopic data, which was supported by theoretical calculations. The current knowledge of the structure, function, and spectroscopic characterization of the CuZ center is described here. We would like to stress that although many questions have been answered, the CuZ center remains a scientific challenge, with many hypotheses still being formed.
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Affiliation(s)
- Simone Dell'Acqua
- REQUIMTE/CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516, Caparica, Portugal
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20
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Dell’Acqua S, Pauleta SR, Monzani E, Pereira AS, Casella L, Moura JJG, Moura I. Electron Transfer Complex between Nitrous Oxide Reductase and Cytochrome c552 from Pseudomonas nautica: Kinetic, Nuclear Magnetic Resonance, and Docking Studies. Biochemistry 2008; 47:10852-62. [DOI: 10.1021/bi801375q] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Simone Dell’Acqua
- REQUIMTE/CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal, and Dipartimento di Chimica Generale, Università di Pavia, Via Taramelli 12, 27100 Pavia, Italy
| | - Sofia R. Pauleta
- REQUIMTE/CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal, and Dipartimento di Chimica Generale, Università di Pavia, Via Taramelli 12, 27100 Pavia, Italy
| | - Enrico Monzani
- REQUIMTE/CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal, and Dipartimento di Chimica Generale, Università di Pavia, Via Taramelli 12, 27100 Pavia, Italy
| | - Alice S. Pereira
- REQUIMTE/CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal, and Dipartimento di Chimica Generale, Università di Pavia, Via Taramelli 12, 27100 Pavia, Italy
| | - Luigi Casella
- REQUIMTE/CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal, and Dipartimento di Chimica Generale, Università di Pavia, Via Taramelli 12, 27100 Pavia, Italy
| | - José J. G. Moura
- REQUIMTE/CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal, and Dipartimento di Chimica Generale, Università di Pavia, Via Taramelli 12, 27100 Pavia, Italy
| | - Isabel Moura
- REQUIMTE/CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal, and Dipartimento di Chimica Generale, Università di Pavia, Via Taramelli 12, 27100 Pavia, Italy
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Fujita K, Chan JM, Bollinger JA, Alvarez ML, Dooley DM. Anaerobic purification, characterization and preliminary mechanistic study of recombinant nitrous oxide reductase from Achromobacter cycloclastes. J Inorg Biochem 2007; 101:1836-44. [PMID: 17681606 DOI: 10.1016/j.jinorgbio.2007.06.029] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2007] [Revised: 06/04/2007] [Accepted: 06/06/2007] [Indexed: 11/20/2022]
Abstract
An overexpression system for nitrous oxide reductase (N(2)OR), an enzyme that catalyzes the conversion of N(2)O to N(2) and H(2)O, has been developed in Achromobacter cycloclastes. Anaerobically purified A. cycloclastes recombinant N(2)OR (AcN(2)OR) has on average 4.5 Cu and 1.2 S per monomer. Upon reduction by methyl viologen, AcN(2)OR displays a high specific activity: 124 U/mg at 25 degrees C. Anaerobically purified AcN(2)OR displays a unique absorption spectrum. UV-visible and EPR spectra, combined with kinetics studies, indicate that the as-purified form of the enzyme is predominately a mixture of the fully-reduced Cu(Z)=[4Cu(I)] state and the Cu(Z)=[3Cu(I).Cu(II)] state, with the latter readily reducible by reduced forms of viologens. CD spectra of the as-purified AcN(2)OR over a range of pH values reveal perturbations of the protein conformation induced by pH variations, although the principal secondary structure elements are largely unaltered. Further, the activity of AcN(2)OR in D(2)O is significantly decreased compared with that in H(2)O, indicative of a significant solvent isotope effect on N(2)O reduction. These data are in good agreement with conclusions reached in recent studies on the effect of pH on catalysis by N(2)OR [K. Fujita, D.M. Dooley, Inorg. Chem. 46 (2007) 613-615].
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Affiliation(s)
- Koyu Fujita
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, USA
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22
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Zumft WG, Kroneck PMH. Respiratory transformation of nitrous oxide (N2O) to dinitrogen by Bacteria and Archaea. Adv Microb Physiol 2006; 52:107-227. [PMID: 17027372 DOI: 10.1016/s0065-2911(06)52003-x] [Citation(s) in RCA: 197] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
N2O is a potent greenhouse gas and stratospheric reactant that has been steadily on the rise since the beginning of industrialization. It is an obligatory inorganic metabolite of denitrifying bacteria, and some production of N2O is also found in nitrifying and methanotrophic bacteria. We focus this review on the respiratory aspect of N2O transformation catalysed by the multicopper enzyme nitrous oxide reductase (N2OR) that provides the bacterial cell with an electron sink for anaerobic growth. Two types of Cu centres discovered in N2OR were both novel structures among the Cu proteins: the mixed-valent dinuclear Cu(A) species at the electron entry site of the enzyme, and the tetranuclear Cu(Z) centre as the first catalytically active Cu-sulfur complex known. Several accessory proteins function as Cu chaperone and ABC transporter systems for the biogenesis of the catalytic centre. We describe here the paradigm of Z-type N2OR, whose characteristics have been studied in most detail in the genera Pseudomonas and Paracoccus. Sequenced bacterial genomes now provide an invaluable additional source of information. New strains harbouring nos genes and capability of N2O utilization are being uncovered. This reveals previously unknown relationships and allows pattern recognition and predictions. The core nos genes, nosZDFYL, share a common phylogeny. Most principal taxonomic lineages follow the same biochemical and genetic pattern and share the Z-type enzyme. A modified N2OR is found in Wolinella succinogenes, and circumstantial evidence also indicates for certain Archaea another type of N2OR. The current picture supports the view of evolution of N2O respiration prior to the separation of the domains Bacteria and Archaea. Lateral nos gene transfer from an epsilon-proteobacterium as donor is suggested for Magnetospirillum magnetotacticum and Dechloromonas aromatica. In a few cases, nos gene clusters are plasmid borne. Inorganic N2O metabolism is associated with a diversity of physiological traits and biochemically challenging metabolic modes or habitats, including halorespiration, diazotrophy, symbiosis, pathogenicity, psychrophily, thermophily, extreme halophily and the marine habitat down to the greatest depth. Components for N2O respiration cover topologically the periplasm and the inner and outer membranes. The Sec and Tat translocons share the task of exporting Nos components to their functional sites. Electron donation to N2OR follows pathways with modifications depending on the host organism. A short chronology of the field is also presented.
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Affiliation(s)
- Walter G Zumft
- Institute of Applied Biosciences, Division of Molecular Microbiology, University of Karlsruhe, D-76128 Karlsruhe, Germany
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Zumft WG. Biogenesis of the bacterial respiratory CuA, Cu-S enzyme nitrous oxide reductase. J Mol Microbiol Biotechnol 2006; 10:154-66. [PMID: 16645312 DOI: 10.1159/000091562] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Nitrous oxide reductase (NosZ, EC 1.7.99.6) is the terminal oxidoreductase of a respiratory electron transfer chain that transforms nitrous oxide to dinitrogen. The enzyme carries six Cu atoms. Two are arranged in the mixed-valent binuclear CuA site, and four make up the mu4-sulfide-bridged Cu cluster, CuZ. The biogenesis of a catalytically active NosZ requires auxiliary functions for metal center assembly in the periplasm. Both Tat and Sec pathways share the task to transport the various Nos proteins to their functional sites. Biogenesis of NosZ requires an ABC transporter complex and the periplasmic Cu chaperone NosL. Sustaining whole-cell NosZ function depends on the periplasmic, FAD-containing protein NosX, and the membrane-bound iron-sulfur flavoprotein NosR. Most components with a biogenetic function are now amenable to structural studies.
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Affiliation(s)
- Walter G Zumft
- Institute of Applied Biosciences, Division of Molecular Microbiology, University of Karlsruhe, Karlsruhe, Germany.
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