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Kikuchi S, Fujitani H, Ishii K, Isshiki R, Sekiguchi Y, Tsuneda S. Characterisation of bacteria representing a novel Nitrosomonas clade: Physiology, genomics and distribution of missing ammonia oxidizer. ENVIRONMENTAL MICROBIOLOGY REPORTS 2023; 15:404-416. [PMID: 37078228 PMCID: PMC10472526 DOI: 10.1111/1758-2229.13158] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2023] [Accepted: 04/12/2023] [Indexed: 05/03/2023]
Abstract
Members of the genus Nitrosomonas are major ammonia oxidizers that catalyse the first step of nitrification in various ecosystems. To date, six subgenus-level clades have been identified. We have previously isolated novel ammonia oxidizers from an additional clade (unclassified cluster 1) of the genus Nitrosomonas. In this study, we report unique physiological and genomic properties of the strain PY1, compared with representative ammonia-oxidising bacteria (AOB). The apparent half-saturation constant for total ammonia nitrogen and maximum velocity of strain PY1 were 57.9 ± 4.8 μM NH3 + NH4 + and 18.5 ± 1.8 μmol N (mg protein)-1 h-1 , respectively. Phylogenetic analysis based on genomic information revealed that strain PY1 belongs to a novel clade of the Nitrosomonas genus. Although PY1 contained genes to withstand oxidative stress, cell growth of PY1 required catalase to scavenge hydrogen peroxide. Environmental distribution analysis revealed that the novel clade containing PY1-like sequences is predominant in oligotrophic freshwater. Taken together, the strain PY1 had a longer generation time, higher yield and required reactive oxygen species (ROS) scavengers to oxidize ammonia, compared with known AOB. These findings expand our knowledge of the ecophysiology and genomic diversity of ammonia-oxidising Nitrosomonas.
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Affiliation(s)
- Shuta Kikuchi
- Department of Life Science and Medical BioscienceWaseda UniversityTokyoJapan
| | - Hirotsugu Fujitani
- Department of Biological SciencesChuo UniversityTokyoJapan
- Research Organization for Nano & Life InnovationWaseda UniversityTokyoJapan
| | - Kento Ishii
- Department of Life Science and Medical BioscienceWaseda UniversityTokyoJapan
- Research Organization for Nano & Life InnovationWaseda UniversityTokyoJapan
| | - Rino Isshiki
- Department of Life Science and Medical BioscienceWaseda UniversityTokyoJapan
| | - Yuji Sekiguchi
- Biomedical Research InstituteNational Institute of Advanced Industrial Science and Technology (AIST)IbarakiJapan
| | - Satoshi Tsuneda
- Department of Life Science and Medical BioscienceWaseda UniversityTokyoJapan
- Research Organization for Nano & Life InnovationWaseda UniversityTokyoJapan
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2
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Bloomer BJ, Natoli SN, Garcia-Borràs M, Pereira JH, Hu DB, Adams PD, Houk KN, Clark DS, Hartwig JF. Mechanistic and structural characterization of an iridium-containing cytochrome reveals kinetically relevant cofactor dynamics. Nat Catal 2023. [DOI: 10.1038/s41929-022-00899-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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3
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Abendroth J, Buchko GW, Liew FN, Nguyen JN, Kim HJ. Structural Characterization of Cytochrome c'β-Met from an Ammonia-Oxidizing Bacterium. Biochemistry 2022; 61:563-574. [PMID: 35315646 DOI: 10.1021/acs.biochem.1c00640] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The ammonia-oxidizing bacterium Nitrosomonas europaea expresses two cytochromes in the P460 superfamily that are predicted to be structurally similar. In one, cytochrome (cyt) P460, the substrate hydroxylamine (NH2OH) is converted to nitric oxide (NO) and nitrous oxide (N2O) requiring a unique heme-lysyl cross-link in the catalytic cofactor. In the second, cyt c'β-Met, the cross-link is absent, and the cytochrome instead binds H2O2 forming a ferryl species similar to compound II of peroxidases. Here, we report the 1.80 Å crystal structure of cyt c'β-Met─a well-expressed protein in N. europaea with a lysine to a methionine replacement at the cross-linking position. The structure of cyt c'β-Met is characterized by a large β-sheet typical of P460 members; however, several localized structural differences render cyt c'β-Met distinct. This includes a large lasso-like loop at the "top" of the cytochrome that is not observed in other structurally characterized members. Active site variation is also observed, especially in comparison to its closest homologue cyt c'β from the methane-oxidizing Methylococcus capsulatus Bath, which also lacks the cross-link. The phenylalanine "cap" which is presumed to control small ligand access to the distal heme iron is replaced with an arginine, reminiscent of the strictly conserved distal arginine in peroxidases and to the NH2OH-oxidizing cytochromes P460. A critical proton-transferring glutamate residue required for NH2OH oxidation is nevertheless missing in the active site. This in part explains the inability of cyt c'β-Met to oxidize NH2OH. Our structure also rationalizes the absence of a methionyl cross-link, although the side chain's spatial position in the structure does not eliminate the possibility that it could form under certain conditions.
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Affiliation(s)
- Jan Abendroth
- Seattle Structural Genomics Center for Infectious Diseases, Seattle, Washington 98105, United States.,UCB Biosciences, Bainbridge Island, Washington 98110, United States
| | - Garry W Buchko
- Seattle Structural Genomics Center for Infectious Diseases, Seattle, Washington 98105, United States.,Earth and Biological Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 98354, United States.,School of Molecular Biosciences, Washington State University, Pullman, Washington 99164, United States
| | - Fong Ning Liew
- Division of Physical Sciences, Chemistry, University of Washington-Bothell, Bothell, Washington 98011, United States
| | - Joline N Nguyen
- Division of Physical Sciences, Chemistry, University of Washington-Bothell, Bothell, Washington 98011, United States
| | - Hyung J Kim
- Division of Physical Sciences, Chemistry, University of Washington-Bothell, Bothell, Washington 98011, United States
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4
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Abstract
Ammonia-oxidizing bacteria (AOB) convert ammonia (NH3) to nitrite (NO2-) as their primary metabolism and thus provide a blueprint for the use of NH3 as a chemical fuel. The first energy-producing step involves the homotrimeric enzyme hydroxylamine oxidoreductase (HAO), which was originally reported to oxidize hydroxylamine (NH2OH) to NO2-. HAO uses the heme P460 cofactor as the site of catalysis. This heme is supported by seven other c hemes in each monomer that mediate electron transfer. Heme P460 cofactors are c-heme-based cofactors that have atypical protein cross-links between the peptide backbone and the porphyrin macrocycle. This cofactor has been observed in both the HAO and cytochrome (cyt) P460 protein families. However, there are differences; specifically, HAO uses a single tyrosine residue to form two covalent attachments to the macrocycle whereas cyt P460 uses a lysine residue to form one. In Nitrosomonas europaea, which expresses both HAO and cyt P460, these enzymes achieve the oxidation of NH2OH and were both originally reported to produce NO2-. Each can inspire means to effect controlled release of chemical energy.Spectroscopically studying the P460 cofactors of HAO is complicated by the 21 non-P460 heme cofactors, which obscure the active site. However, monoheme cyt P460 is more approachable biochemically and spectroscopically. Thus, we have used cyt P460 to study biological NH2OH oxidation. Under aerobic conditions substoichiometric production of NO2- was observed along with production of nitrous oxide (N2O). Under anaerobic conditions, however, N2O was the exclusive product of NH2OH oxidation. We have advanced our understanding of the mechanism of this enzyme and have showed that a key intermediate is a ferric nitrosyl that can dissociate the bound nitric oxide (NO) molecule and react with O2, thus producing NO2- abiotically. Because N2O was the true product of one P460 cofactor-containing enzyme, this prompted us to reinvestigate whether NO2- is enzymatically generated from HAO catalysis. Like cyt P460, we showed that HAO does not produce NO2- enzymatically, but unlike cyt P460, its final product is NO, establishing it as an intermediate of nitrification. More broadly, NO can be recognized as a molecule common to the primary metabolisms of all organisms involved in nitrogen "defixation".Delving deeper into cyt P460 yielded insights broadly applicable to controlled biochemical redox processes. Studies of an inactive cyt P460 from Nitrosomonas sp. AL212 showed that this enzyme was unable to oxidize NH2OH because it lacked a glutamate residue in its secondary coordination sphere that was present in the active N. europaea cyt P460 variant. Restoring the Glu residue imbued activity, revealing that a second-sphere base is Nature's key to controlled oxidation of NH2OH. A key lesson of bioinorganic chemistry is reinforced: the polypeptide matrix is an essential part of dictating function. Our work also exposed some key functional contributions of noncanonical heme-protein cross-links. The heme-Lys cross-link of cyt P460 enforces the relative position of the cofactor and second-sphere residues. Moreover, the cross-link prevents the dissociation of the axial histidine residue, which stops catalysis, emphasizing the importance of this unique post-translational modification.
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Affiliation(s)
- Rachael E. Coleman
- Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - Kyle M. Lancaster
- Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
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5
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Ferousi C, Majer SH, DiMucci IM, Lancaster KM. Biological and Bioinspired Inorganic N-N Bond-Forming Reactions. Chem Rev 2020; 120:5252-5307. [PMID: 32108471 PMCID: PMC7339862 DOI: 10.1021/acs.chemrev.9b00629] [Citation(s) in RCA: 46] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The metallobiochemistry underlying the formation of the inorganic N-N-bond-containing molecules nitrous oxide (N2O), dinitrogen (N2), and hydrazine (N2H4) is essential to the lifestyles of diverse organisms. Similar reactions hold promise as means to use N-based fuels as alternative carbon-free energy sources. This review discusses research efforts to understand the mechanisms underlying biological N-N bond formation in primary metabolism and how the associated reactions are tied to energy transduction and organismal survival. These efforts comprise studies of both natural and engineered metalloenzymes as well as synthetic model complexes.
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Affiliation(s)
- Christina Ferousi
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, United States
| | - Sean H Majer
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, United States
| | - Ida M DiMucci
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, United States
| | - Kyle M Lancaster
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, United States
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6
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Coleman RE, Vilbert AC, Lancaster KM. The Heme-Lys Cross-Link in Cytochrome P460 Promotes Catalysis by Enforcing Secondary Coordination Sphere Architecture. Biochemistry 2020; 59:2289-2298. [PMID: 32525655 DOI: 10.1021/acs.biochem.0c00261] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Cytochrome (cyt) P460 is a c-type monoheme enzyme found in ammonia-oxidizing bacteria (AOB) and methanotrophs; additionally, genes encoding it have been found in some pathogenic bacteria. Cyt P460 is defined by a unique post-translational modification to the heme macrocycle, where a lysine (Lys) residue covalently attaches to the 13' meso carbon of the porphyrin, modifying this heme macrocycle into the enzyme's eponymous P460 cofactor, similar to the cofactor found in the enzyme hydroxylamine oxidoreductase. This cross-link imbues the protein with unique spectroscopic properties, the most obvious of which is the enzyme's green color in solution. Cyt P460 from the AOB Nitrosomonas europaea is a homodimeric redox enzyme that produces nitrous oxide (N2O) from 2 equiv of hydroxylamine. Mutation of the Lys cross-link results in spectroscopic features that are more similar to those of standard cyt c' proteins and renders the enzyme catalytically incompetent for NH2OH oxidation. Recently, the necessity of a second-sphere glutamate (Glu) residue for redox catalysis was established; it plausibly serves as proton relay during the first oxidative half of the catalytic cycle. Herein, we report the first crystal structure of a cross-link deficient cyt P460. This structure shows that the positioning of the catalytically essential Glu changes by approximately 0.8 Å when compared to a cross-linked, catalytically competent cyt P460. It appears that the heme-Lys cross-link affects the relative position of the P460 cofactor with respect to the second-sphere Glu residue, therefore dictating the catalytic competency of the enzyme.
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Affiliation(s)
- Rachael E Coleman
- Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - Avery C Vilbert
- Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - Kyle M Lancaster
- Baker Laboratory, Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
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7
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Liew FN, Brandys MA, Biswas S, Nguyen JN, Rahmawati M, Nevala M, Elmore BO, Hendrich MP, Kim HJ. Cytochrome c' β-Met Is a Variant in the P460 Superfamily Lacking the Heme-Lysyl Cross-Link: A Peroxidase Mimic Generating a Ferryl Intermediate. Biochemistry 2020; 59:704-716. [PMID: 31887031 DOI: 10.1021/acs.biochem.9b00810] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A defining characteristic of bacterial cytochromes (cyt's) in the P460 family is an unusual cross-link connecting the heme porphyrin to the side chain of a lysyl residue in the protein backbone. Here, via proteomics of the periplasmic fraction of the ammonia-oxidizing bacterium (AOB) Nitrosomonas europaea, we report the identification of a variant member of the P460 family that contains a methionyl residue in place of the cross-linking lysine. We formally designate this protein cytochrome "c'β-Met" to distinguish it from other members bearing different residues at this position (e.g., cyt c'β-Phe from the methane-oxidizing Methylococcus capsulatus Bath). As isolated, the monoheme cyt c'β-Met is high-spin (S = 5/2). Optical spectroscopy suggests that a cross-link is absent. Hydroxylamine, the substrate for the cross-linked cyt P460 from N. europaea, did not appreciably alter the optical spectrum of cyt c'β with up to 1000-fold excess at pH 7.5. Cyt c'β-Met did however bind 1 equiv of H2O2, and with a slight excess, Mössbauer spectroscopy indicated the formation of a semistable ferryl (FeIV═O) Compound II-like species. The corresponding electron paramagnetic resonance showed a very low intensity signal indicative of a radical at g = 2.0. Furthermore, cyt c'β-Met exhibited guaiacol-dependent peroxidase activity (kcat = 20.0 ± 1.2 s-1; KM = 2.6 ± 0.4 mM). Unlike cyt c'β-Met, cyt P460 showed evidence of heme inactivation in the presence of 2 equiv of H2O2 with no appreciable guaiacol-dependent peroxidase activity. Mutagenesis of the cross-linking lysyl residue to an alanine in cyt P460, however, reversed this lack of activity.
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Affiliation(s)
- Fong Ning Liew
- Division of Physical Sciences, Chemistry , University of Washington Bothell , Bothell , Washington 98012 , United States
| | - Marisa A Brandys
- Division of Physical Sciences, Chemistry , University of Washington Bothell , Bothell , Washington 98012 , United States
| | - Saborni Biswas
- Department of Chemistry , Carnegie Mellon University , Pittsburgh , Pennsylvania 15213 , United States
| | - Joline N Nguyen
- Division of Physical Sciences, Chemistry , University of Washington Bothell , Bothell , Washington 98012 , United States
| | - Mustika Rahmawati
- Division of Physical Sciences, Chemistry , University of Washington Bothell , Bothell , Washington 98012 , United States
| | - Michael Nevala
- Division of Physical Sciences, Chemistry , University of Washington Bothell , Bothell , Washington 98012 , United States.,Veolia Nuclear Solutions Federal Solutions , Richland , Washington 99354 , United States
| | - Bradley O Elmore
- Newport Laboratories , Worthington , Minnesota 56187 , United States
| | - Michael P Hendrich
- Department of Chemistry , Carnegie Mellon University , Pittsburgh , Pennsylvania 15213 , United States
| | - Hyung J Kim
- Division of Physical Sciences, Chemistry , University of Washington Bothell , Bothell , Washington 98012 , United States
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8
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Ehudin MA, Senft L, Franke A, Ivanović-Burmazović I, Karlin KD. Formation and Reactivity of New Isoporphyrins: Implications for Understanding the Tyr-His Cross-Link Cofactor Biogenesis in Cytochrome c Oxidase. J Am Chem Soc 2019; 141:10632-10643. [PMID: 31150209 DOI: 10.1021/jacs.9b01791] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Cytochrome c oxidase (CcO) catalyzes the reduction of dioxygen to water utilizing a heterobinuclear active site composed of a heme moiety and a mononuclear copper center coordinated to three histidine residues, one of which is covalently cross-linked to a tyrosine residue via a post-translational modification (PTM). Although this tyrosine-histidine moiety has functional and structural importance, the pathway behind this net oxidative C-N bond coupling is still unknown. A novel route employing an iron(III) meso-substituted isoporphyrin derivative, isoelectronic with Cmpd-I ((Por•+)FeIV═O), is for the first time proposed to be a key intermediate in the Tyr-His cofactor biogenesis. Newly synthesized iron(III) meso-substituted isoporphyrins were prepared with azide, cyanide, and substituted imidazole functionalities, by adding nucleophiles to an iron(III) π-dication species formed via addition of trifluoroacetic acid to F8Cmpd-I (F8 = (tetrakis(2,6-difluorophenyl)porphyrinate)). Isoporphyrin derivatives were characterized at cryogenic temperatures via ESI-MS and UV-vis, 2H NMR, and EPR spectroscopies. Addition of 1,3,5-trimethoxybenzene or 4-methoxyphenol to the imidazole-substituted isoporphyrin led to formation of the organic product containing the imidazole coupled to aromatic substrate via a new C-N bond, as detected via cryo-ESI-MS. Experimental evidence for the formation of an imidazole-substituted isoporphyrin and its promising reactivity to form the imidazole-phenol coupled product yields viability to the herein proposed pathway behind the PTM (i.e., biogenesis) leading to the key covalent Tyr-His cross-link in CcO.
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Affiliation(s)
- Melanie A Ehudin
- Department of Chemistry , Johns Hopkins University , Baltimore , Maryland 21218 , United States
| | - Laura Senft
- Department of Chemistry and Pharmacy , Friedrich-Alexander University Erlangen-Nuremberg , 91058 Erlangen , Germany
| | - Alicja Franke
- Department of Chemistry and Pharmacy , Friedrich-Alexander University Erlangen-Nuremberg , 91058 Erlangen , Germany
| | - Ivana Ivanović-Burmazović
- Department of Chemistry and Pharmacy , Friedrich-Alexander University Erlangen-Nuremberg , 91058 Erlangen , Germany
| | - Kenneth D Karlin
- Department of Chemistry , Johns Hopkins University , Baltimore , Maryland 21218 , United States
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9
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Smith MA, Majer SH, Vilbert AC, Lancaster KM. Controlling a burn: outer-sphere gating of hydroxylamine oxidation by a distal base in cytochrome P460. Chem Sci 2019; 10:3756-3764. [PMID: 31015919 PMCID: PMC6457333 DOI: 10.1039/c9sc00195f] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2019] [Accepted: 02/14/2019] [Indexed: 01/19/2023] Open
Abstract
One amino acid makes the difference between a metalloenzyme and a metalloprotein in two otherwise effectively identical cytochrome P460s.
Ammonia oxidizing bacteria (AOB) use the cytotoxic, energetic molecule hydroxylamine (NH2OH) as a source of reducing equivalents for cellular respiration. Despite disproportionation or violent decomposition being typical outcomes of reactions of NH2OH with iron, AOB and anammox heme P460 proteins including cytochrome (cyt) P460 and hydroxylamine oxidoreductase (HAO) effect controlled, stepwise oxidation of NH2OH to nitric oxide (NO). Curiously, a recently characterized cyt P460 variant from the AOB Nitrosomonas sp. AL212 is able to form all intermediates of cyt P460 catalysis, but is nevertheless incompetent for NH2OH oxidation. We now show via site-directed mutagenesis, activity assays, spectroscopy, and structural biology that this lack of activity is attributable to the absence of a critical basic glutamate residue in the distal pocket above the heme P460 cofactor. This substitution is the only distinguishing characteristic of a protein that is otherwise effectively structurally and spectroscopically identical to an active variant. This highlights and reinforces a fundamental principal of metalloenzymology: metallocofactor inner-sphere geometric and electronic structures are in many cases insufficient for imbuing reactivity; a precisely defined outer coordination sphere contributed by the polypeptide matrix can be the key differentiator between a metalloenzyme and an unreactive metalloprotein.
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Affiliation(s)
- Meghan A Smith
- Department of Chemistry and Chemical Biology , Baker Laboratory , Cornell University , Ithaca , NY 14853 , USA .
| | - Sean H Majer
- Department of Chemistry and Chemical Biology , Baker Laboratory , Cornell University , Ithaca , NY 14853 , USA .
| | - Avery C Vilbert
- Department of Chemistry and Chemical Biology , Baker Laboratory , Cornell University , Ithaca , NY 14853 , USA .
| | - Kyle M Lancaster
- Department of Chemistry and Chemical Biology , Baker Laboratory , Cornell University , Ithaca , NY 14853 , USA .
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10
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New metal cofactors and recent metallocofactor insights. Curr Opin Struct Biol 2019; 59:1-8. [PMID: 30711735 DOI: 10.1016/j.sbi.2018.12.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Accepted: 12/20/2018] [Indexed: 11/23/2022]
Abstract
A vast array of metal cofactors are associated with the active sites of metalloenzymes. This Opinion describes the most recently discovered metal cofactor, a nickel-pincer nucleotide (NPN) coenzyme that is covalently tethered to lactate racemase from Lactobacillus plantarum. The enzymatic function of the NPN cofactor and its pathway for biosynthesis are reviewed. Furthermore, insights are summarized from recent advances involving other selected organometallic and inorganic-cluster cofactors including the lanthanide-pyrroloquinoline quinone found in certain alcohol dehydrogenases, tungsten-pyranopterins or molybdenum-pyranopterins in chosen enzymes, the iron-guanylylpyridinol cofactor of [Fe] hydrogenase, the nickel-tetrapyrrole coenzyme F430 of methyl coenzyme M reductase, the vanadium-iron cofactor of nitrogenase, redox-dependent rearrangements of the nickel-iron-sulfur C-cluster in carbon monoxide dehydrogenase, and light-dependent changes in the multi-manganese cluster of the oxygen-evolving complex.
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11
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Adams HR, Krewson C, Vardanega JE, Fujii S, Moreno-Chicano T, Moreno T, Chicano, Sambongi Y, Svistunenko D, Paps J, Andrew CR, Hough MA. One fold, two functions: cytochrome P460 and cytochrome c'-β from the methanotroph Methylococcus capsulatus (Bath). Chem Sci 2019; 10:3031-3041. [PMID: 30996884 PMCID: PMC6427953 DOI: 10.1039/c8sc05210g] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2018] [Accepted: 01/20/2019] [Indexed: 11/21/2022] Open
Abstract
Nature is adept at utilising highly similar protein folds to carry out very different functions, yet the mechanisms by which this functional divergence occurs remain poorly characterised. In certain methanotrophic bacteria, two homologous pentacoordinate c-type heme proteins have been identified: a cytochrome P460 (cyt P460) and a cytochrome c'-β (cyt cp-β). Cytochromes P460 are able to convert hydroxylamine to nitrous oxide (N2O), a potent greenhouse gas. This reactivity is similar to that of hydroxylamine oxidoreductase (HAO), which is a key enzyme in nitrifying and methanotrophic bacteria. Cyt P460 and HAO both have unusual protein-heme cross-links, formed by a Tyr residue in HAO and a Lys in cyt P460. In contrast, cyts cp-β (the only known cytochromes c' with a β-sheet fold) lack this crosslink and appears to be optimized for binding non-polar molecules (including NO and CO) without enzymatic conversion. Our bioinformatics analysis supports the proposal that cyt cp-β may have evolved from cyt P460 via a gene duplication event. Using high-resolution X-ray crystallography, UV-visible absorption, electron paramagnetic resonance (EPR) and resonance Raman spectroscopy, we have characterized the overall protein folding and active site structures of cyt cp-β and cyt P460 from the obligate methanotroph, Methylococcus capsulatus (Bath). These proteins display a similar β-sheet protein fold, together with a pattern of changes to the heme pocket regions and localised tertiary structure that have converted a hydroxylamine oxidizing enzyme into a gas-binding protein. Structural comparisons provide insights relevant to enzyme redesign for synthetic enzymology and engineering of gas sensor proteins. We also show the widespread occurrence of cyts cp-β and characterise their phylogeny.
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Affiliation(s)
- Hannah R Adams
- School of Biological Sciences , University of Essex , Wivenhoe Park , Colchester , Essex CO4 3SQ , UK .
| | - Callie Krewson
- Department of Chemistry and Biochemistry , Eastern Oregon University , La Grande , Oregon 97850 , USA .
| | - Jenny E Vardanega
- Department of Chemistry and Biochemistry , Eastern Oregon University , La Grande , Oregon 97850 , USA .
| | - Sotaro Fujii
- Graduate School of Biosphere Science , Hiroshima University , Kagamiyama 1-4-4, Higashi-Hiroshima , Hiroshima , 739-8528 , Japan
| | | | - Tadeo Moreno
- School of Biological Sciences , University of Essex , Wivenhoe Park , Colchester , Essex CO4 3SQ , UK .
| | - Chicano
- School of Biological Sciences , University of Essex , Wivenhoe Park , Colchester , Essex CO4 3SQ , UK .
| | - Yoshihiro Sambongi
- Graduate School of Biosphere Science , Hiroshima University , Kagamiyama 1-4-4, Higashi-Hiroshima , Hiroshima , 739-8528 , Japan
| | - Dimitri Svistunenko
- School of Biological Sciences , University of Essex , Wivenhoe Park , Colchester , Essex CO4 3SQ , UK .
| | - Jordi Paps
- School of Biological Sciences , University of Essex , Wivenhoe Park , Colchester , Essex CO4 3SQ , UK .
| | - Colin R Andrew
- Department of Chemistry and Biochemistry , Eastern Oregon University , La Grande , Oregon 97850 , USA .
| | - Michael A Hough
- School of Biological Sciences , University of Essex , Wivenhoe Park , Colchester , Essex CO4 3SQ , UK .
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