1
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Wojdyla Z, Maldonado-Domínguez M, Bharadwaz P, Culka M, Srnec M. Elucidation of factors shaping reactivity of 5'-deoxyadenosyl - a prominent organic radical in biology. Phys Chem Chem Phys 2024. [PMID: 39041228 DOI: 10.1039/d4cp01725k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/24/2024]
Abstract
This study investigates the factors modulating the reactivity of 5'-deoxyadenosyl (5'dAdo˙) radical, a potent hydrogen atom abstractor that forms in the active sites of radical SAM enzymes and that otherwise undergoes a rapid self-decay in aqueous solution. Here, we compare hydrogen atom abstraction (HAA) reactions between native substrates of radical SAM enzymes and 5'dAdo˙ in aqueous solution and in two enzymatic microenvironments. With that we reveal that HAA efficiency of 5'dAdo˙ is due to (i) the in situ formation of 5'dAdo˙ in a pre-ordered complex with a substrate, which attenuates the unfavorable effect of substrate:5'dAdo˙ complex formation, and (ii) the prevention of the conformational changes associated with self-decay by a tight active-site cavity. The enzymatic cavity, however, does not have a strong effect on the HAA activity of 5'dAdo˙. Thus, we performed an analysis of in-water HAA performed by 5'dAdo˙ based on a three-component thermodynamic model incorporating the diagonal effect of the free energy of reaction, and the off-diagonal effect of asynchronicity and frustration. To this aim, we took advantage of the straightforward relationship between the off-diagonal thermodynamic effects and the electronic-structure descriptor - the redistribution of charge between the reactants during the reaction. It allows to access HAA-competent redox and acidobasic properties of 5'dAdo˙ that are otherwise unavailable due to its instability upon one-electron reduction and protonation. The results show that all reactions feature a favourable thermodynamic driving force and tunneling, the latter of which lowers systematically barriers by ∼2 kcal mol-1. In addition, most of the reactions experience a favourable off-diagonal thermodynamic contribution. In HAA reactions, 5'dAdo˙ acts as a weak oxidant as well as a base, also 5'dAdo˙-promoted HAA reactions proceed with a quite low degree of asynchronicity of proton and electron transfer. Finally, the study elucidates the crucial and dual role of asynchronicity. It directly lowers the barrier as a part of the off-diagonal thermodynamic contribution, but also indirectly increases the non-thermodynamic part of the barrier by presumably controlling the adiabatic coupling between proton and electron transfer. The latter signals that the reaction proceeds as a hydrogen atom transfer rather than a proton-coupled electron transfer.
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Affiliation(s)
- Zuzanna Wojdyla
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, 18200 Prague, Czech Republic.
| | - Mauricio Maldonado-Domínguez
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, 18200 Prague, Czech Republic.
| | - Priyam Bharadwaz
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, 18200 Prague, Czech Republic.
| | - Martin Culka
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám. 2, 16610 Prague, Czech Republic
| | - Martin Srnec
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, 18200 Prague, Czech Republic.
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2
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Szaleniec M, Oleksy G, Sekuła A, Aleksić I, Pietras R, Sarewicz M, Krämer K, Pierik AJ, Heider J. Modeling the Initiation Phase of the Catalytic Cycle in the Glycyl-Radical Enzyme Benzylsuccinate Synthase. J Phys Chem B 2024; 128:5823-5839. [PMID: 38848492 PMCID: PMC11194802 DOI: 10.1021/acs.jpcb.4c01237] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2024] [Revised: 05/15/2024] [Accepted: 05/16/2024] [Indexed: 06/09/2024]
Abstract
The reaction of benzylsuccinate synthase, the radical-based addition of toluene to a fumarate cosubstrate, is initiated by hydrogen transfer from a conserved cysteine to the nearby glycyl radical in the active center of the enzyme. In this study, we analyze this step by comprehensive computer modeling, predicting (i) the influence of bound substrates or products, (ii) the energy profiles of forward- and backward hydrogen-transfer reactions, (iii) their kinetic constants and potential mechanisms, (iv) enantiospecificity differences, and (v) kinetic isotope effects. Moreover, we support several of the computational predictions experimentally, providing evidence for the predicted H/D-exchange reactions into the product and at the glycyl radical site. Our data indicate that the hydrogen transfer reactions between the active site glycyl and cysteine are principally reversible, but their rates differ strongly depending on their stereochemical orientation, transfer of protium or deuterium, and the presence or absence of substrates or products in the active site. This is particularly evident for the isotope exchange of the remaining protium atom of the glycyl radical to deuterium, which appears dependent on substrate or product binding, explaining why the exchange is observed in some, but not all, glycyl-radical enzymes.
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Affiliation(s)
- Maciej Szaleniec
- Jerzy
Haber Institute of Catalysis and Surface Chemistry, Polish Academy
of Sciences, Kraków 31-201, Poland
| | - Gabriela Oleksy
- Jerzy
Haber Institute of Catalysis and Surface Chemistry, Polish Academy
of Sciences, Kraków 31-201, Poland
- Department
of Biology, Laboratory for Microbial Biochemistry, Philipps University Marburg, Marburg 35043, Germany
| | - Anna Sekuła
- Jerzy
Haber Institute of Catalysis and Surface Chemistry, Polish Academy
of Sciences, Kraków 31-201, Poland
| | - Ivana Aleksić
- Jerzy
Haber Institute of Catalysis and Surface Chemistry, Polish Academy
of Sciences, Kraków 31-201, Poland
| | - Rafał Pietras
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Kraków 31-007, Poland
| | - Marcin Sarewicz
- Department
of Molecular Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Kraków 31-007, Poland
| | - Kai Krämer
- Department
of Biology, Laboratory for Microbial Biochemistry, Philipps University Marburg, Marburg 35043, Germany
| | - Antonio J. Pierik
- Biochemistry,
Faculty of ChemistryRPTU Kaiserslautern-Landau, Kaiserslautern D-67663, Germany
| | - Johann Heider
- Department
of Biology, Laboratory for Microbial Biochemistry, Philipps University Marburg, Marburg 35043, Germany
- Synmikro-Center
for Synthetic Microbiology, Philipps University
Marburg, Marburg 35043, Germany
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3
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Kammel M, Erdmann C, Sawers RG. The formate-hydrogen axis and its impact on the physiology of enterobacterial fermentation. Adv Microb Physiol 2024; 84:51-82. [PMID: 38821634 DOI: 10.1016/bs.ampbs.2024.02.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/02/2024]
Abstract
Formic acid (HCOOH) and dihydrogen (H2) are characteristic products of enterobacterial mixed-acid fermentation, with H2 generation increasing in conjunction with a decrease in extracellular pH. Formate and acetyl-CoA are generated by radical-based and coenzyme A-dependent cleavage of pyruvate catalysed by pyruvate formate-lyase (PflB). Formate is also the source of H2, which is generated along with carbon dioxide through the action of the membrane-associated, cytoplasmically-oriented formate hydrogenlyase (FHL-1) complex. Synthesis of the FHL-1 complex is completely dependent on the cytoplasmic accumulation of formate. Consequently, formate determines its own disproportionation into H2 and CO2 by the FHL-1 complex. Cytoplasmic formate levels are controlled by FocA, a pentameric channel that translocates formic acid/formate bidirectionally between the cytoplasm and periplasm. Each protomer of FocA has a narrow hydrophobic pore through which neutral formic acid can pass. Two conserved amino acid residues, a histidine and a threonine, at the center of the pore control directionality of translocation. The histidine residue is essential for pH-dependent influx of formic acid. Studies with the formate analogue hypophosphite and amino acid variants of FocA suggest that the mechanisms of formic acid efflux and influx differ. Indeed, current data suggest, depending on extracellular formate levels, two separate uptake mechanisms exist, both likely contributing to maintain pH homeostasis. Bidirectional formate/formic acid translocation is dependent on PflB and influx requires an active FHL-1 complex. This review describes the coupling of formate and H2 production in enterobacteria.
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Affiliation(s)
- Michelle Kammel
- Institute of Microbiology, Martin Luther University Halle-Wittenberg, Halle, Saale, Germany
| | - Christopher Erdmann
- Institute of Microbiology, Martin Luther University Halle-Wittenberg, Halle, Saale, Germany
| | - R Gary Sawers
- Institute of Microbiology, Martin Luther University Halle-Wittenberg, Halle, Saale, Germany.
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4
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Yang H, Ho MB, Lundahl MN, Mosquera MA, Broderick WE, Broderick JB, Hoffman BM. ENDOR Spectroscopy Reveals the "Free" 5'-Deoxyadenosyl Radical in a Radical SAM Enzyme Active Site Actually is Chaperoned by Close Interaction with the Methionine-Bound [4Fe-4S] 2+ Cluster. J Am Chem Soc 2024; 146:3710-3720. [PMID: 38308759 DOI: 10.1021/jacs.3c09428] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2024]
Abstract
1/2H and 13C hyperfine coupling constants to 5'-deoxyadenosyl (5'-dAdo•) radical trapped within the active site of the radical S-adenosyl-l-methionine (SAM) enzyme, pyruvate formate lyase-activating enzyme (PFL-AE), both in the absence of substrate and the presence of a reactive peptide-model of the PFL substrate, are completely characteristic of a classical organic free radical whose unpaired electron is localized in the 2pπ orbital of the sp2 C5'-carbon (J. Am. Chem. Soc. 2019, 141, 12139-12146). However, prior electron-nuclear double resonance (ENDOR) measurements had indicated that this 5'-dAdo• free radical is never truly "free": tight van der Waals contact with its target partners and active-site residues guide it in carrying out the exquisitely precise, regioselective reactions that are hallmarks of RS enzymes. Here, our understanding of how the active site chaperones 5'-dAdo• is extended through the finding that this apparently unexceptional organic free radical has an anomalous g-tensor and exhibits significant 57Fe, 13C, 15N, and 2H hyperfine couplings to the adjacent, isotopically labeled, methionine-bound [4Fe-4S]2+ cluster cogenerated with 5'-dAdo• during homolytic cleavage of cluster-bound SAM. The origin of the 57Fe couplings through nonbonded radical-cluster contact is illuminated by a formal exchange-coupling model and broken symmetry-density functional theory computations. Incorporation of ENDOR-derived distances from C5'(dAdo•) to labeled-methionine as structural constraints yields a model for active-site positioning of 5'-dAdo• with a short, nonbonded C5'-Fe distance (∼3 Å). This distance involves substantial motion of 5'-dAdo• toward the unique Fe of the [4Fe-4S]2+ cluster upon S-C(5') bond-cleavage, plausibly an initial step toward formation of the Fe-C5' bond of the organometallic complex, Ω, the central intermediate in catalysis by radical-SAM enzymes.
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Affiliation(s)
- Hao Yang
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Madeline B Ho
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Maike N Lundahl
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Martín A Mosquera
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - William E Broderick
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Joan B Broderick
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Brian M Hoffman
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
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5
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Xu L, Wu Y, Yang X, Pang X, Wu Y, Li X, Liu X, Zhao Y, Yu L, Wang P, Ye B, Jiang S, Ma J, Zhang X. The Fe-S cluster biosynthesis in Enterococcus faecium is essential for anaerobic growth and gastrointestinal colonization. Gut Microbes 2024; 16:2359665. [PMID: 38831611 PMCID: PMC11152105 DOI: 10.1080/19490976.2024.2359665] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/10/2024] [Accepted: 05/21/2024] [Indexed: 06/05/2024] Open
Abstract
The facultative anaerobic Gram-positive bacterium Enterococcus faecium is a ubiquitous member of the human gut microbiota. However, it has gradually evolved into a pathogenic and multidrug resistant lineage that causes nosocomial infections. The establishment of high-level intestinal colonization by enterococci represents a critical step of infection. The majority of current research on Enterococcus has been conducted under aerobic conditions, while limited attention has been given to its physiological characteristics in anaerobic environments, which reflects its natural colonization niche in the gut. In this study, a high-density transposon mutant library containing 26,620 distinct insertion sites was constructed. Tn-seq analysis identified six genes that significantly contribute to growth under anaerobic conditions. Under anaerobic conditions, deletion of sufB (encoding Fe-S cluster assembly protein B) results in more extensive and significant impairments on carbohydrate metabolism compared to aerobic conditions. Consistently, the pathways involved in this utilization-restricted carbohydrates were mostly expressed at significantly lower levels in mutant compared to wild-type under anaerobic conditions. Moreover, deletion of sufB or pflA (encoding pyruvate formate lyase-activating protein A) led to failure of gastrointestinal colonization in mice. These findings contribute to our understanding of the mechanisms by which E. faecium maintains proliferation under anaerobic conditions and establishes colonization in the gut.
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Affiliation(s)
- Linan Xu
- College of Agriculture and Forestry, Linyi University, Linyi, China
- Department of Preventive Veterinary Medicine, College of Veterinary Medicine, Shandong Agricultural University, Tai’an, China
| | - Yajing Wu
- Department of Food Science and Nutrition, Zhejiang University, Hangzhou, China
| | - Xiangpeng Yang
- College of Agriculture and Forestry, Linyi University, Linyi, China
| | - Xinxin Pang
- State Key Laboratory of Microbial Technology, Shandong University, Qingdao, China
| | - Yansha Wu
- Institute of Edible Fungi, Shanghai Academy of Agricultural Sciences, Shanghai, China
| | - Xingshuai Li
- College of Agriculture and Forestry, Linyi University, Linyi, China
| | - Xiayu Liu
- Department of Food Science and Nutrition, Zhejiang University, Hangzhou, China
| | - Yuzhong Zhao
- College of Agriculture and Forestry, Linyi University, Linyi, China
- Department of Preventive Veterinary Medicine, College of Veterinary Medicine, Shandong Agricultural University, Tai’an, China
| | - Lumin Yu
- College of Agriculture and Forestry, Linyi University, Linyi, China
| | - Peikun Wang
- College of Agriculture and Forestry, Linyi University, Linyi, China
| | - Bin Ye
- College of Agriculture and Forestry, Linyi University, Linyi, China
| | - Shijin Jiang
- Department of Preventive Veterinary Medicine, College of Veterinary Medicine, Shandong Agricultural University, Tai’an, China
| | - Junfei Ma
- College of Agriculture and Forestry, Linyi University, Linyi, China
| | - Xinglin Zhang
- College of Agriculture and Forestry, Linyi University, Linyi, China
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6
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Lachowicz J, Lee J, Sagatova A, Jew K, Grove TL. The new epoch of structural insights into radical SAM enzymology. Curr Opin Struct Biol 2023; 83:102720. [PMID: 37862762 DOI: 10.1016/j.sbi.2023.102720] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2023] [Revised: 09/21/2023] [Accepted: 09/22/2023] [Indexed: 10/22/2023]
Abstract
The Radical SAM (RS) superfamily of enzymes catalyzes a wide array of enzymatic reactions. The majority of these enzymes employ an electron from a reduced [4Fe-4S]+1 cluster to facilitate the reductive cleavage of S-adenosyl-l-methionine, thereby producing a highly reactive 5'-deoxyadenosyl radical (5'-dA⋅) and l-methionine. Typically, RS enzymes use this 5'-dA⋅ to extract a hydrogen atom from the target substrate, starting the cascade of an expansive and impressive variety of chemical transformations. While a great deal of understanding has been gleaned for 5'-dA⋅ formation, because of the chemical diversity within this superfamily, the subsequent chemical transformations have only been fully elucidated in a few examples. In addition, with the advent of new sequencing technology, the size of this family now surpasses 700,000 members, with the number of uncharacterized enzymes and domains also rapidly expanding. In this review, we outline the history of RS enzyme characterization in what we term "epochs" based on advances in technology designed for stably producing these enzymes in an active state. We propose that the state of the field has entered the fourth epoch, which we argue should commence with a protein structure initiative focused solely on RS enzymes to properly tackle this unique superfamily and uncover more novel chemical transformations that likely exist.
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Affiliation(s)
- Jake Lachowicz
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - James Lee
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Alia Sagatova
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Kristen Jew
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Tyler L Grove
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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7
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Benjdia A, Berteau O. B 12-dependent radical SAM enzymes: Ever expanding structural and mechanistic diversity. Curr Opin Struct Biol 2023; 83:102725. [PMID: 37931378 DOI: 10.1016/j.sbi.2023.102725] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2023] [Revised: 09/26/2023] [Accepted: 10/03/2023] [Indexed: 11/08/2023]
Abstract
In the last decade, B12-dependent radical SAM enzymes have emerged as central biocatalysts in the biosynthesis of a myriad of natural products. Notably, these enzymes have been shown to catalyze carbon-carbon bond formation on unactivated carbon atoms leading to unusual methylations. Recently, structural studies have revealed unprecedented insights into the complex chemistry catalyzed by these enzymes. In this review, we cover recent advances in our understanding of B12-dependent radical SAM enzymes from a mechanistic and structural perspective. We discuss the unanticipated diversity of these enzymes which suggests evolutionary links between various biosynthetic and metabolic pathways from antibiotic to RiPP and methane biosynthesis.
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Affiliation(s)
- Alhosna Benjdia
- Université Paris-Saclay, INRAE, AgroParisTech, Micalis Institute, ChemSyBio, 78350, Jouy-en-Josas, France.
| | - Olivier Berteau
- Université Paris-Saclay, INRAE, AgroParisTech, Micalis Institute, ChemSyBio, 78350, Jouy-en-Josas, France.
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8
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Lundahl MN, Yang H, Broderick WE, Hoffman BM, Broderick JB. Pyruvate formate-lyase activating enzyme: The catalytically active 5'-deoxyadenosyl radical caught in the act of H-atom abstraction. Proc Natl Acad Sci U S A 2023; 120:e2314696120. [PMID: 37956301 PMCID: PMC10665898 DOI: 10.1073/pnas.2314696120] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2023] [Accepted: 10/03/2023] [Indexed: 11/15/2023] Open
Abstract
Enzymes of the radical S-adenosyl-l-methionine (radical SAM, RS) superfamily, the largest in nature, catalyze remarkably diverse reactions initiated by H-atom abstraction. Glycyl radical enzyme activating enzymes (GRE-AEs) are a growing class of RS enzymes that generate the catalytically essential glycyl radical of GREs, which in turn catalyze essential reactions in anaerobic metabolism. Here, we probe the reaction of the GRE-AE pyruvate formate-lyase activating enzyme (PFL-AE) with the peptide substrate RVSG734YAV, which mimics the site of glycyl radical formation on the native substrate, pyruvate formate-lyase. Time-resolved freeze-quench electron paramagnetic resonance spectroscopy shows that at short mixing times reduced PFL-AE + SAM reacts with RVSG734YAV to form the central organometallic intermediate, Ω, in which the adenosyl 5'C is covalently bound to the unique iron of the [4Fe-4S] cluster. Freeze-trapping the reaction at longer times reveals the formation of the peptide G734• glycyl radical product. Of central importance, freeze-quenching at intermediate times reveals that the conversion of Ω to peptide glycyl radical is not concerted. Instead, homolysis of the Ω Fe-C5' bond generates the nominally "free" 5'-dAdo• radical, which is captured here by freeze-trapping. During cryoannealing at 77 K, the 5'-dAdo• directly abstracts an H-atom from the peptide to generate the G734• peptide radical trapped in the PFL-AE active site. These observations reveal the 5'-dAdo• radical to be a well-defined intermediate, caught in the act of substrate H-atom abstraction, providing new insights into the mechanistic steps of radical initiation by RS enzymes.
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Affiliation(s)
- Maike N. Lundahl
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT59717
| | - Hao Yang
- Department of Chemistry, Northwestern University, Evanston, IL60208
| | - William E. Broderick
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT59717
| | - Brian M. Hoffman
- Department of Chemistry, Northwestern University, Evanston, IL60208
| | - Joan B. Broderick
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT59717
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9
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Cáceres JC, Dolmatch A, Greene BL. The Mechanism of Inhibition of Pyruvate Formate Lyase by Methacrylate. J Am Chem Soc 2023; 145:22504-22515. [PMID: 37797332 PMCID: PMC10591478 DOI: 10.1021/jacs.3c07256] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2023] [Indexed: 10/07/2023]
Abstract
Pyruvate Formate Lyase (PFL) catalyzes acetyl transfer from pyruvate to coenzyme a by a mechanism involving multiple amino acid radicals. A post-translationally installed glycyl radical (G734· in Escherichia coli) is essential for enzyme activity and two cysteines (C418 and C419) are proposed to form thiyl radicals during turnover, yet their unique roles in catalysis have not been directly demonstrated with both structural and electronic resolution. Methacrylate is an isostructural analog of pyruvate and an informative irreversible inhibitor of pfl. Here we demonstrate the mechanism of inhibition of pfl by methacrylate. Treatment of activated pfl with methacrylate results in the conversion of the G734· to a new radical species, concomitant with enzyme inhibition, centered at g = 2.0033. Spectral simulations, reactions with methacrylate isotopologues, and Density Functional Theory (DFT) calculations support our assignment of the radical to a C2 tertiary methacryl radical. The reaction is specific for C418, as evidenced by mass spectrometry. The methacryl radical decays over time, reforming G734·, and the decay exhibits a H/D solvent isotope effect of 3.4, consistent with H-atom transfer from an ionizable donor, presumably the C419 sulfhydryl group. Acrylate also inhibits PFL irreversibly, and alkylates C418, but we did not observe an acryl secondary radical in H2O or in D2O within 10 s, consistent with our DFT calculations and the expected reactivity of a secondary versus tertiary carbon-centered radical. Together, the results support unique roles of the two active site cysteines of PFL and a C419 S-H bond dissociation energy between that of a secondary and tertiary C-H bond.
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Affiliation(s)
- Juan Carlos Cáceres
- Biomolecular
Science and Engineering Program, University
of California, Santa
Barbara, California 93106, United States
| | - August Dolmatch
- Department
of Chemistry and Biochemistry, University
of California, Santa Barbara, California 93106, United States
| | - Brandon L. Greene
- Biomolecular
Science and Engineering Program, University
of California, Santa
Barbara, California 93106, United States
- Department
of Chemistry and Biochemistry, University
of California, Santa Barbara, California 93106, United States
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10
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Abstract
Radical S-adenosylmethionine (SAM) enzymes use a site-differentiated [4Fe-4S] cluster and SAM to initiate radical reactions through liberation of the 5'-deoxyadenosyl (5'-dAdo•) radical. They form the largest enzyme superfamily, with more than 700,000 unique sequences currently, and their numbers continue to grow as a result of ongoing bioinformatics efforts. The range of extremely diverse, highly regio- and stereo-specific reactions known to be catalyzed by radical SAM superfamily members is remarkable. The common mechanism of radical initiation in the radical SAM superfamily is the focus of this review. Most surprising is the presence of an organometallic intermediate, Ω, exhibiting an Fe-C5'-adenosyl bond. Regioselective reductive cleavage of the SAM S-C5' bond produces 5'-dAdo• to form Ω, with the regioselectivity originating in the Jahn-Teller effect. Ω liberates the free 5'-dAdo• as the catalytically active intermediate through homolysis of the Fe-C5' bond, in analogy to Co-C5' bond homolysis in B12, which was once viewed as biology's choice of radical generator.
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Affiliation(s)
- Brian M Hoffman
- Department of Chemistry, Northwestern University, Evanston, Illinois, USA
| | - William E Broderick
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana, USA;
| | - Joan B Broderick
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana, USA;
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11
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Andorfer MC, King-Roberts DT, Imrich CN, Brotheridge BG, Drennan CL. Development of an in vitro method for activation of X-succinate synthases for fumarate hydroalkylation. iScience 2023; 26:106902. [PMID: 37283811 PMCID: PMC10239695 DOI: 10.1016/j.isci.2023.106902] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Revised: 05/08/2023] [Accepted: 05/12/2023] [Indexed: 06/08/2023] Open
Abstract
Anaerobic microbial degradation of hydrocarbons is often initiated through addition of the hydrocarbon to fumarate by enzymes known as X-succinate synthases (XSSs). XSSs use a glycyl radical cofactor, which is installed by an activating enzyme (XSS-AE), to catalyze this carbon-carbon coupling reaction. The activation step, although crucial for catalysis, has not previously been possible in vitro because of insolubility of XSS-AEs. Here, we take a genome mining approach to find an XSS-AE, a 4-isopropylbenzylsuccinate synthase (IBSS)-AE (IbsAE) that can be solubly expressed in Escherichia coli. This soluble XSS-AE can activate both IBSS and the well-studied benzylsuccinate synthase (BSS) in vitro, allowing us to explore XSSs biochemically. To start, we examine the role of BSS subunits and find that the beta subunit accelerates the rate of hydrocarbon addition. Looking forward, the methodology and insight gathered here can be used more broadly to understand and engineer XSSs as synthetically useful biocatalysts.
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Affiliation(s)
- Mary C. Andorfer
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Devin T. King-Roberts
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Christa N. Imrich
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Balyn G. Brotheridge
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Catherine L. Drennan
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Center for Environmental Health, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Bio-inspired Solar Energy Program, Canadian Institute for Advanced Research (CIFAR), Toronto, ON M5G 1M1, Canada
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12
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Moody JD, Hill S, Lundahl MN, Saxton AJ, Galambas A, Broderick WE, Lawrence CM, Broderick JB. Computational engineering of previously crystallized pyruvate formate-lyase activating enzyme reveals insights into SAM binding and reductive cleavage. J Biol Chem 2023; 299:104791. [PMID: 37156396 PMCID: PMC10267522 DOI: 10.1016/j.jbc.2023.104791] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2023] [Revised: 04/21/2023] [Accepted: 04/23/2023] [Indexed: 05/10/2023] Open
Abstract
Radical S-adenosyl-l-methionine (SAM) enzymes are ubiquitous in nature and carry out a broad variety of difficult chemical transformations initiated by hydrogen atom abstraction. Although numerous radical SAM (RS) enzymes have been structurally characterized, many prove recalcitrant to crystallization needed for atomic-level structure determination using X-ray crystallography, and even those that have been crystallized for an initial study can be difficult to recrystallize for further structural work. We present here a method for computationally engineering previously observed crystallographic contacts and employ it to obtain more reproducible crystallization of the RS enzyme pyruvate formate-lyase activating enzyme (PFL-AE). We show that the computationally engineered variant binds a typical RS [4Fe-4S]2+/+ cluster that binds SAM, with electron paramagnetic resonance properties indistinguishable from the native PFL-AE. The variant also retains the typical PFL-AE catalytic activity, as evidenced by the characteristic glycyl radical electron paramagnetic resonance signal observed upon incubation of the PFL-AE variant with reducing agent, SAM, and PFL. The PFL-AE variant was also crystallized in the [4Fe-4S]2+ state with SAM bound, providing a new high-resolution structure of the SAM complex in the absence of substrate. Finally, by incubating such a crystal in a solution of sodium dithionite, the reductive cleavage of SAM is triggered, providing us with a structure in which the SAM cleavage products 5'-deoxyadenosine and methionine are bound in the active site. We propose that the methods described herein may be useful in the structural characterization of other difficult-to-resolve proteins.
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Affiliation(s)
- James D Moody
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah, USA; Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana, USA
| | - Sarah Hill
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana, USA
| | - Maike N Lundahl
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana, USA
| | - Aubrianna J Saxton
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah, USA
| | - Amanda Galambas
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana, USA
| | - William E Broderick
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana, USA
| | - C Martin Lawrence
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana, USA
| | - Joan B Broderick
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana, USA.
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13
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Huang R, Zhi N, Yu L, Li Y, Wu X, He J, Zhu H, Qiao J, Liu X, Tian C, Wang J, Dong M. Genetically Encoded Photosensitizer Protein Reduces Iron–Sulfur Clusters of Radical SAM Enzymes. ACS Catal 2023. [DOI: 10.1021/acscatal.2c05143] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Affiliation(s)
- Rongrong Huang
- Frontiers Science Center for Synthetic Biology, Key Laboratory of Systems Bioengineering (MOE), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Ning Zhi
- Frontiers Science Center for Synthetic Biology, Key Laboratory of Systems Bioengineering (MOE), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Lu Yu
- High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei, Anhui 230031, China
| | - Yaoyang Li
- Frontiers Science Center for Synthetic Biology, Key Laboratory of Systems Bioengineering (MOE), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Xiangyu Wu
- Frontiers Science Center for Synthetic Biology, Key Laboratory of Systems Bioengineering (MOE), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Jiale He
- Frontiers Science Center for Synthetic Biology, Key Laboratory of Systems Bioengineering (MOE), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Hongji Zhu
- Frontiers Science Center for Synthetic Biology, Key Laboratory of Systems Bioengineering (MOE), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Jianjun Qiao
- Frontiers Science Center for Synthetic Biology, Key Laboratory of Systems Bioengineering (MOE), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
| | - Xiaohong Liu
- Laboratory of RNA Biology, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
| | - Changlin Tian
- High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei, Anhui 230031, China
- The First Affiliated Hospital of USTC, School of Life Sciences, Division of Life Sciences and Medicine, Joint Center for Biological Analytical Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Jiangyun Wang
- Laboratory of RNA Biology, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
| | - Min Dong
- Frontiers Science Center for Synthetic Biology, Key Laboratory of Systems Bioengineering (MOE), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
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14
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Quick and Spontaneous Transformation between [3Fe-4S] and [4Fe-4S] Iron-Sulfur Clusters in the tRNA-Thiolation Enzyme TtuA. Int J Mol Sci 2023; 24:ijms24010833. [PMID: 36614280 PMCID: PMC9821441 DOI: 10.3390/ijms24010833] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2022] [Revised: 12/16/2022] [Accepted: 12/26/2022] [Indexed: 01/06/2023] Open
Abstract
Iron-sulfur (Fe-S) clusters are essential cofactors for enzyme activity. These Fe-S clusters are present in structurally diverse forms, including [4Fe-4S] and [3Fe-4S]. Type-identification of the Fe-S cluster is indispensable in understanding the catalytic mechanism of enzymes. However, identifying [4Fe-4S] and [3Fe-4S] clusters in particular is challenging because of their rapid transformation in response to oxidation-reduction events. In this study, we focused on the relationship between the Fe-S cluster type and the catalytic activity of a tRNA-thiolation enzyme (TtuA). We reconstituted [4Fe-4S]-TtuA, prepared [3Fe-4S]-TtuA by oxidizing [4Fe-4S]-TtuA under strictly anaerobic conditions, and then observed changes in the Fe-S clusters in the samples and the enzymatic activity in the time-course experiments. Electron paramagnetic resonance analysis revealed that [3Fe-4S]-TtuA spontaneously transforms into [4Fe-4S]-TtuA in minutes to one hour without an additional free Fe source in the solution. Although the TtuA immediately after oxidation of [4Fe-4S]-TtuA was inactive [3Fe-4S]-TtuA, its activity recovered to a significant level compared to [4Fe-4S]-TtuA after one hour, corresponding to an increase of [4Fe-4S]-TtuA in the solution. Our findings reveal that [3Fe-4S]-TtuA is highly inactive and unstable. Moreover, time-course analysis of structural changes and activity under strictly anaerobic conditions further unraveled the Fe-S cluster type used by the tRNA-thiolation enzyme.
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15
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Broderick JB, Broderick WE, Hoffman BM. Radical SAM enzymes: Nature's choice for radical reactions. FEBS Lett 2023; 597:92-101. [PMID: 36251330 PMCID: PMC9894703 DOI: 10.1002/1873-3468.14519] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2022] [Accepted: 10/05/2022] [Indexed: 02/04/2023]
Abstract
Enzymes that use a [4Fe-4S]1+ cluster plus S-adenosyl-l-methionine (SAM) to initiate radical reactions (radical SAM) form the largest enzyme superfamily, with over half a million members across the tree of life. This review summarizes recent work revealing the radical SAM reaction pathway, which ultimately liberates the 5'-deoxyadenosyl (5'-dAdo•) radical to perform extremely diverse, highly regio- and stereo-specific, transformations. Most surprising was the discovery of an organometallic intermediate Ω exhibiting an Fe-C5'-adenosyl bond. Ω liberates 5'-dAdo• through homolysis of the Fe-C5' bond, in analogy to Co-C5' bond homolysis in B12 , previously viewed as biology's paradigmatic radical generator. The 5'-dAdo• has been trapped and characterized in radical SAM enzymes via a recently discovered photoreactivity of the [4Fe-4S]+ /SAM complex, and has been confirmed as a catalytically active intermediate in enzyme catalysis. The regioselective SAM S-C bond cleavage to produce 5'-dAdo• originates in the Jahn-Teller effect. The simplicity of SAM as a radical precursor, and the exquisite control of 5'-dAdo• reactivity in radical SAM enzymes, may be why radical SAM enzymes pervade the tree of life, while B12 enzymes are only a few.
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Affiliation(s)
- Joan B. Broderick
- Department of Chemistry & Biochemistry, 103 CBB, Montana State University, Bozeman, MT 59717
| | - William E. Broderick
- Department of Chemistry & Biochemistry, 103 CBB, Montana State University, Bozeman, MT 59717
| | - Brian M. Hoffman
- Department of Chemistry, 2145 Sheridan Rd, Northwestern University, Evanston, IL. 60208
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16
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Kammel M, Pinske C, Sawers RG. FocA and its central role in fine-tuning pH homeostasis of enterobacterial formate metabolism. MICROBIOLOGY (READING, ENGLAND) 2022; 168. [PMID: 36197793 DOI: 10.1099/mic.0.001253] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
During enterobacterial mixed-acid fermentation, formate is generated from pyruvate by the glycyl-radical enzyme pyruvate formate-lyase (PflB). In Escherichia coli, especially at low pH, formate is then disproportionated to CO2 and H2 by the cytoplasmically oriented, membrane-associated formate hydrogenlyase (FHL) complex. If electron acceptors are available, however, formate is oxidized by periplasmically oriented, respiratory formate dehydrogenases. Formate translocation across the cytoplasmic membrane is controlled by the formate channel, FocA, a member of the formate-nitrite transporter (FNT) family of homopentameric anion channels. This review highlights recent advances in our understanding of how FocA helps to maintain intracellular formate and pH homeostasis during fermentation. Efflux and influx of formate/formic acid are distinct processes performed by FocA and both are controlled through protein interaction between FocA's N-terminal domain with PflB. Formic acid efflux by FocA helps to maintain cytoplasmic pH balance during exponential-phase growth. Uptake of formate against the electrochemical gradient (inside negative) is energetically and mechanistically challenging for a fermenting bacterium unless coupled with proton/cation symport. Translocation of formate/formic acid into the cytoplasm necessitates an active FHL complex, whose synthesis also depends on formate. Thus, FocA, FHL and PflB function together to govern formate homeostasis. We explain how FocA achieves efflux of formic acid and propose mechanisms for pH-dependent uptake of formate both with and without proton symport. We propose that FocA displays both channel- and transporter-like behaviour. Whether this translocation behaviour is shared by other members of the FNT family is also discussed.
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Affiliation(s)
- Michelle Kammel
- Institute of Microbiology, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Constanze Pinske
- Institute of Microbiology, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - R Gary Sawers
- Institute of Microbiology, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
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17
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Gagsteiger J, Jahn S, Heidinger L, Gericke L, Andexer JN, Friedrich T, Loenarz C, Layer G. A Cobalamin-Dependent Radical SAM Enzyme Catalyzes the Unique C α -Methylation of Glutamine in Methyl-Coenzyme M Reductase. Angew Chem Int Ed Engl 2022; 61:e202204198. [PMID: 35638156 PMCID: PMC9401015 DOI: 10.1002/anie.202204198] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2022] [Indexed: 12/22/2022]
Abstract
Methyl‐coenzyme M reductase, which is responsible for the production of the greenhouse gas methane during biological methane formation, carries several unique posttranslational amino acid modifications, including a 2‐(S)‐methylglutamine. The enzyme responsible for the Cα‐methylation of this glutamine is not known. Herein, we identify and characterize a cobalamin‐dependent radical SAM enzyme as the glutamine C‐methyltransferase. The recombinant protein from Methanoculleus thermophilus binds cobalamin in a base‐off, His‐off conformation and contains a single [4Fe‐4S] cluster. The cobalamin cofactor cycles between the methyl‐cob(III)alamin, cob(II)alamin and cob(I)alamin states during catalysis and produces methylated substrate, 5′‐deoxyadenosine and S‐adenosyl‐l‐homocysteine in a 1 : 1 : 1 ratio. The newly identified glutamine C‐methyltransferase belongs to the class B radical SAM methyltransferases known to catalyze challenging methylation reactions of sp3‐hybridized carbon atoms.
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Affiliation(s)
- Jana Gagsteiger
- Institut für Pharmazeutische Wissenschaften, Pharmazeutische Biologie, Albert-Ludwigs-Universität Freiburg, Stefan-Meier-Str. 19, 79104, Freiburg, Germany
| | - Sören Jahn
- Institut für Pharmazeutische Wissenschaften, Pharmazeutische und Medizinische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 25, 79104, Freiburg, Germany
| | - Lorenz Heidinger
- Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, 79104, Freiburg, Germany
| | - Lukas Gericke
- Institut für Pharmazeutische Wissenschaften, Pharmazeutische und Medizinische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 25, 79104, Freiburg, Germany
| | - Jennifer N Andexer
- Institut für Pharmazeutische Wissenschaften, Pharmazeutische und Medizinische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 25, 79104, Freiburg, Germany
| | - Thorsten Friedrich
- Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, 79104, Freiburg, Germany
| | - Christoph Loenarz
- Institut für Pharmazeutische Wissenschaften, Pharmazeutische und Medizinische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 25, 79104, Freiburg, Germany
| | - Gunhild Layer
- Institut für Pharmazeutische Wissenschaften, Pharmazeutische Biologie, Albert-Ludwigs-Universität Freiburg, Stefan-Meier-Str. 19, 79104, Freiburg, Germany
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18
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Hanževački M, Croft AK, Jäger CM. Activation of Glycyl Radical Enzymes─Multiscale Modeling Insights into Catalysis and Radical Control in a Pyruvate Formate-Lyase-Activating Enzyme. J Chem Inf Model 2022; 62:3401-3414. [PMID: 35771966 PMCID: PMC9326890 DOI: 10.1021/acs.jcim.2c00362] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Pyruvate formate-lyase (PFL) is a glycyl radical enzyme (GRE) playing a pivotal role in the metabolism of strict and facultative anaerobes. Its activation is carried out by a PFL-activating enzyme, a member of the radical S-adenosylmethionine (rSAM) superfamily of metalloenzymes, which introduces a glycyl radical into the Gly radical domain of PFL. The activation mechanism is still not fully understood and is structurally based on a complex with a short model peptide of PFL. Here, we present extensive molecular dynamics simulations in combination with quantum mechanics/molecular mechanics (QM/MM)-based kinetic and thermodynamic reaction evaluations of a more complete activation model comprising the 49 amino acid long C-terminus region of PFL. We reveal the benefits and pitfalls of the current activation model, providing evidence that the bound peptide conformation does not resemble the bound protein-protein complex conformation with PFL, with implications for the activation process. Substitution of the central glycine with (S)- and (R)-alanine showed excellent binding of (R)-alanine over unstable binding of (S)-alanine. Radical stabilization calculations indicate that a higher radical stability of the glycyl radical might not be the sole origin of the evolutionary development of GREs. QM/MM-derived radical formation kinetics further demonstrate feasible activation barriers for both peptide and C-terminus activation, demonstrating why the crystalized model peptide system is an excellent inhibitory system for natural activation. This new evidence supports the theory that GREs converged on glycyl radical formation due to the better conformational accessibility of the glycine radical loop, rather than the highest radical stability of the formed peptide radicals.
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Affiliation(s)
- Marko Hanževački
- Department of Chemical and Environmental Engineering, University of Nottingham, Nottingham NG7 2RD, U.K
| | - Anna K Croft
- Department of Chemical and Environmental Engineering, University of Nottingham, Nottingham NG7 2RD, U.K
| | - Christof M Jäger
- Department of Chemical and Environmental Engineering, University of Nottingham, Nottingham NG7 2RD, U.K
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19
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Bridwell-Rabb J, Li B, Drennan CL. Cobalamin-Dependent Radical S-Adenosylmethionine Enzymes: Capitalizing on Old Motifs for New Functions. ACS BIO & MED CHEM AU 2022; 2:173-186. [PMID: 35726326 PMCID: PMC9204698 DOI: 10.1021/acsbiomedchemau.1c00051] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 01/08/2022] [Accepted: 01/10/2022] [Indexed: 01/21/2023]
Abstract
The members of the radical S-adenosylmethionine (SAM) enzyme superfamily are responsible for catalyzing a diverse set of reactions in a multitude of biosynthetic pathways. Many members of this superfamily accomplish their transformations using the catalytic power of a 5'-deoxyadenosyl radical (5'-dAdo•), but there are also enzymes within this superfamily that bind auxiliary cofactors and extend the catalytic repertoire of SAM. In particular, the cobalamin (Cbl)-dependent class synergistically uses Cbl to facilitate challenging methylation and radical rearrangement reactions. Despite identification of this class by Sofia et al. 20 years ago, the low sequence identity between members has led to difficulty in predicting function of uncharacterized members, pinpointing catalytic residues, and elucidating reaction mechanisms. Here, we capitalize on the three recent structures of Cbl-dependent radical SAM enzymes that use common cofactors to facilitate ring contraction as well as radical-based and non-radical-based methylation reactions. With these three structures as a framework, we describe how the Cbl-dependent radical SAM enzymes repurpose the traditional SAM- and Cbl-binding motifs to form an active site where both Cbl and SAM can participate in catalysis. In addition, we describe how, in some cases, the classic SAM- and Cbl-binding motifs support the diverse functionality of this enzyme class, and finally, we define new motifs that are characteristic of Cbl-dependent radical SAM enzymes.
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Affiliation(s)
- Jennifer Bridwell-Rabb
- Department
of Chemistry, University of Michigan, 930 N University Avenue, Ann Arbor, Michigan 48109, United States,
| | - Bin Li
- Department
of Chemistry, University of Michigan, 930 N University Avenue, Ann Arbor, Michigan 48109, United States
| | - Catherine L. Drennan
- Department
of Chemistry, Massachusetts Institute of
Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States,Department
of Biology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States,Howard
Hughes Medical Institute, Massachusetts
Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
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20
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Gagsteiger J, Jahn S, Heidinger L, Gericke L, Andexer JN, Friedrich T, Loenarz C, Layer G. A Cobalamin‐Dependent Radical SAM Enzyme Catalyzes the Unique Cα‐Methylation of Glutamine in Methyl‐Coenzyme M Reductase. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202204198] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Jana Gagsteiger
- Albert-Ludwigs-Universität Freiburg, Fakultät für Chemie und Pharmazie Institut für Pharmazeutische Wissenschaften, Pharmazeutische Biologie GERMANY
| | - Sören Jahn
- Albert-Ludwigs-Universität Freiburg, Fakultät für Chemie und Pharmazie Institut für Pharmazeutische Wissenschaften, Pharmazeutische und Medizinische Chemie GERMANY
| | - Lorenz Heidinger
- Albert-Ludwigs-Universität Freiburg Institut für Biochemie GERMANY
| | - Lukas Gericke
- Albert-Ludwigs-Universität Freiburg, Fakultät für Chemie und Pharmazie Institut für Pharmazeutische Wissenschaften, Pharmazeutische und Medizinische Chemie GERMANY
| | - Jennifer N. Andexer
- Albert-Ludwigs-Universität Freiburg, Fakultät für Chemie und Pharmazie Institut für Pharmazeutische Wissenschaften, Pharmazeutische und Medizinische Chemie GERMANY
| | - Thorsten Friedrich
- Albert-Ludwigs-Universität Freiburg, Fakultät für Chemie und Pharmazie Institut für Biochemie GERMANY
| | - Christoph Loenarz
- Albert-Ludwigs-Universität Freiburg, Fakultät für Chemie und Pharmazie Institut für Pharmazeutische Wissenschaften, Pharmazeutische und Medizinische Chemie GERMANY
| | - Gunhild Layer
- Albert-Ludwigs-Universität Freiburg, Fakultät für Chemie und Pharmazie Institut für Pharmazeutische Wissenschaften, Pharmazeutische Biologie Stefan-Meier-Str. 19 79104 Freiburg GERMANY
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21
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Yan L, Liu Y. Mechanistic Insights into the Anaerobic Degradation of Globally Abundant Dihydroxypropanesulfonate Catalyzed by the DHPS-Sulfolyase (HpsG). J Chem Inf Model 2022; 62:2880-2888. [PMID: 35583151 DOI: 10.1021/acs.jcim.2c00174] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
2(S)-Dihydroxypropanesulfonate (DHPS) is the main abundant organosulfonate in the biosphere generated by the microbial degradation of the abundant organosulfur species 6-deoxy-6-sulfo-d-glucopyranose (sulfoquinovose, SQ). Massive amounts of DHPS can also be produced by the highly abundant oceanic diatoms. The quantity of degradation DHPS is so large that it has become an important part of the earth's sulfur. The recently characterized O2-sensitive glycyl radical enzyme DHPS-sulfolyase HpsG in anaerobic bacteria was found to be capable of cleaving the C-S bond of DHPS under anaerobic conditions. However, the detailed degradation mechanism is still unclear. Here, on the basis of the crystal structure of HpsG, we constructed the computational model and performed QM/MM calculations to illuminate the anaerobic degradation mechanism of DHPS. Our calculations revealed that the degradation reaction follows an unusual radical-dependent mechanism that does not require a conserved Glu464 to deprotonate the C2 hydroxyl of substrate to promote the C-S cleavage; instead, after the first hydrogen abstraction triggered by the thiyl radical (Cys462), the C-S bond in 2(S)-dihydroxypropanesulfonate can directly collapse. Thus, conserved Glu464 mainly plays a role in stabilizing the substrate and reaction intermediate by forming a hydrogen bond. After the release of the sulfonic acid group from the protein environment, the deprotonated Glu464 spontaneously accepts a proton from the C2 hydroxyl of the substrate radical. Our findings clarified an unusual C-S cleavage mechanism involved in the DHPS degradation reaction catalyzed by GREs.
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Affiliation(s)
- Lijuan Yan
- School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
| | - Yongjun Liu
- School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China
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22
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The Autonomous Glycyl Radical Protein GrcA Restores Activity to Inactive Full-Length Pyruvate Formate-Lyase In Vivo. J Bacteriol 2022; 204:e0007022. [PMID: 35377165 DOI: 10.1128/jb.00070-22] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
During glucose fermentation, Escherichia coli and many other microorganisms employ the glycyl radical enzyme (GRE) pyruvate formate-lyase (PflB) to catalyze the coenzyme A-dependent cleavage of pyruvate to formate and acetyl-coenzyme A (CoA). Due to its extreme reactivity, the radical in PflB must be controlled carefully and, once generated, is particularly susceptible to dioxygen. Exposure to oxygen of the radical on glycine residue 734 of PflB results in cleavage of the polypeptide chain and consequent inactivation of the enzyme. Two decades ago, a small 14-kDa protein called YfiD (now called autonomous glycyl radical cofactor [GrcA]) was shown to be capable of restoring activity to O2-inactivated PflB in vitro; however, GrcA has never been shown to have this function in vivo. By constructing a strain with a chromosomally encoded PflB enzyme variant with a G734A residue exchange, we could show that cells retained near-wild type fermentative growth, as well as formate and H2 production; H2 is derived by enzymatic disproportionation of formate. Introducing a grcA deletion mutation into this strain completely prevented formate and H2 generation and reduced anaerobic growth. We could show that the conserved glycine at position 102 on GrcA was necessary for GrcA to restore PflB activity and that this recovered activity depended on the essential cysteine residues 418 and 419 in the active site of PflB. Together, our findings demonstrate that GrcA is capable of restoring in vivo activity to inactive full-length PflB and support a model whereby GrcA displaces the C-terminal glycyl radical domain to rescue the catalytic function of PflB. IMPORTANCE Many facultative anaerobic microorganisms use glycyl radical enzymes (GREs) to catalyze chemically challenging reactions under anaerobic conditions. Pyruvate formate-lyase (PflB) is a GRE that catalyzes cleavage of the carbon-carbon bond of pyruvate during glucose fermentation. The problem is that glycyl radicals are destroyed readily, especially by oxygen. To protect and restore activity to inactivated PflB, bacteria like Escherichia coli have a small autonomous glycyl radical cofactor protein called GrcA, which functions to rescue inactivated PflB. To date, this proposed function of GrcA has only been demonstrated in vitro. Our data reveal that GrcA rescues and restores enzyme activity to an inactive full-length form of PflB in vivo. These results have important implications for the evolution of radical-based enzyme mechanisms.
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23
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Liu YA, Quechol R, Solomon JB, Lee CC, Ribbe MW, Hu Y, Hedman B, Hodgson KO. Radical SAM-dependent formation of a nitrogenase cofactor core on NifB. J Inorg Biochem 2022; 233:111837. [PMID: 35550498 PMCID: PMC9526504 DOI: 10.1016/j.jinorgbio.2022.111837] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2021] [Revised: 04/10/2022] [Accepted: 04/14/2022] [Indexed: 11/15/2022]
Abstract
Nitrogenase is a versatile metalloenzyme that reduces N2, CO and CO2 at its cofactor site. Designated the M-cluster, this complex cofactor has a composition of [(R-homocitrate)MoFe7S9C], and it is assembled through the generation of a unique [Fe8S9C] core prior to the insertion of Mo and homocitrate. NifB is a radical S-adenosyl-L-methionine (SAM) enzyme that is essential for nitrogenase cofactor assembly. This review focuses on the recent work that sheds light on the role of NifB in the formation of the [Fe8S9C] core of the nitrogenase cofactor, highlighting the structure, function and mechanism of this unique radical SAM methyltransferase.
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Affiliation(s)
- Yiling A Liu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, United States of America
| | - Robert Quechol
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, United States of America
| | - Joseph B Solomon
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, United States of America; Department of Chemistry, University of California, Irvine, CA 92697-2025, United States of America
| | - Chi Chung Lee
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, United States of America
| | - Markus W Ribbe
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, United States of America; Department of Chemistry, University of California, Irvine, CA 92697-2025, United States of America.
| | - Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, United States of America.
| | - Britt Hedman
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, CA 94025, United States of America.
| | - Keith O Hodgson
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, CA 94025, United States of America; Department of Chemistry, Stanford University, Stanford, CA 94305, United States of America.
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Lundahl MN, Sarksian R, Yang H, Jodts RJ, Pagnier A, Smith DF, Mosquera MA, van der Donk WA, Hoffman BM, Broderick WE, Broderick JB. Mechanism of Radical S-Adenosyl-l-methionine Adenosylation: Radical Intermediates and the Catalytic Competence of the 5'-Deoxyadenosyl Radical. J Am Chem Soc 2022; 144:5087-5098. [PMID: 35258967 PMCID: PMC9524473 DOI: 10.1021/jacs.1c13706] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Radical S-adenosyl-l-methionine (SAM) enzymes employ a [4Fe-4S] cluster and SAM to initiate diverse radical reactions via either H-atom abstraction or substrate adenosylation. Here we use freeze-quench techniques together with electron paramagnetic resonance (EPR) spectroscopy to provide snapshots of the reaction pathway in an adenosylation reaction catalyzed by the radical SAM enzyme pyruvate formate-lyase activating enzyme on a peptide substrate containing a dehydroalanine residue in place of the target glycine. The reaction proceeds via the initial formation of the organometallic intermediate Ω, as evidenced by the characteristic EPR signal with g∥ = 2.035 and g⊥ = 2.004 observed when the reaction is freeze-quenched at 500 ms. Thermal annealing of frozen Ω converts it into a second paramagnetic species centered at giso = 2.004; this second species was generated directly using freeze-quench at intermediate times (∼8 s) and unequivocally identified via isotopic labeling and EPR spectroscopy as the tertiary peptide radical resulting from adenosylation of the peptide substrate. An additional paramagnetic species observed in samples quenched at intermediate times was revealed through thermal annealing while frozen and spectral subtraction as the SAM-derived 5'-deoxyadenosyl radical (5'-dAdo•). The time course of the 5'-dAdo• and tertiary peptide radical EPR signals reveals that the former generates the latter. These results thus support a mechanism in which Ω liberates 5'-dAdo• by Fe-C5' bond homolysis, and the 5'-dAdo• attacks the dehydroalanine residue of the peptide substrate to form the adenosylated peptide radical species. The results thus provide a picture of a catalytically competent 5'-dAdo• intermediate trapped just prior to reaction with the substrate.
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Affiliation(s)
- Maike N. Lundahl
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Raymond Sarksian
- Department of Chemistry and Howard Hughes Medical Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Hao Yang
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Richard J. Jodts
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Adrien Pagnier
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Donald F. Smith
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Martín A. Mosquera
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Wilfred A. van der Donk
- Department of Chemistry and Howard Hughes Medical Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Brian M. Hoffman
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - William E. Broderick
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Joan B. Broderick
- Corresponding Author: Joan B. Broderick – Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States;
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25
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Donnan PH, Mansoorabadi SO. Broken-Symmetry Density Functional Theory Analysis of the Ω Intermediate in Radical S-Adenosyl-l-methionine Enzymes: Evidence for a Near-Attack Conformer over an Organometallic Species. J Am Chem Soc 2022; 144:3381-3385. [PMID: 35170316 DOI: 10.1021/jacs.2c00678] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Radical S-adenosyl-l-methionine (SAM) enzymes are found in all domains of life and catalyze a wide range of biochemical reactions. Recently, an organometallic intermediate, Ω, has been experimentally implicated in the 5'-deoxyadenosyl radical generation mechanism of the radical SAM superfamily. In this work, we employ broken-symmetry density functional theory to evaluate several structural models of Ω. The results show that the calculated hyperfine coupling constants (HFCCs) for the proposed organometallic structure of Ω are inconsistent with the experiment. In contrast, a near-attack conformer of SAM bound to the catalytic [4Fe-4S] cluster, in which the distance between the unique iron and SAM sulfur is ∼3 Å, yields HFCCs that are all within 1 MHz of the experimental values. These results clarify the structure of the ubiquitous Ω intermediate and suggest a paradigm shift reversal regarding the mechanism of SAM cleavage by members of the radical SAM superfamily.
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Affiliation(s)
- Patrick H Donnan
- Department of Chemistry and Biochemistry, Auburn University, 179 Chemistry Building, Auburn, Alabama 36849, United States
| | - Steven O Mansoorabadi
- Department of Chemistry and Biochemistry, Auburn University, 179 Chemistry Building, Auburn, Alabama 36849, United States
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26
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Zhou S, Wei WJ, Liao RZ. QM/MM Study of the Mechanism of the Noncanonical S-Cγ Bond Scission in S-Adenosylmethionine Catalyzed by the CmnDph2 Radical Enzyme. Top Catal 2022. [DOI: 10.1007/s11244-021-01420-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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27
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The B 12-independent glycerol dehydratase activating enzyme from Clostridium butyricum cleaves SAM to produce 5'-deoxyadenosine and not 5'-deoxy-5'-(methylthio)adenosine. J Inorg Biochem 2022; 227:111662. [PMID: 34847521 PMCID: PMC8889718 DOI: 10.1016/j.jinorgbio.2021.111662] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2021] [Revised: 11/04/2021] [Accepted: 11/04/2021] [Indexed: 02/03/2023]
Abstract
Glycerol dehydratase activating enzyme (GD-AE) is a radical S-adenosyl-l-methionine (SAM) enzyme that installs a catalytically essential amino acid backbone radical onto glycerol dehydratase in bacteria under anaerobic conditions. Although GD-AE is closely homologous to other radical SAM activases that have been shown to cleave the S-C(5') bond of SAM to produce 5'-deoxyadenosine (5'-dAdoH) and methionine, GD-AE from Clostridium butyricum has been reported to instead cleave the S-C(γ) bond of SAM to yield 5'-deoxy-5'-(methylthio)adenosine (MTA). Here we re-investigate the SAM cleavage reaction catalyzed by GD-AE and show that it produces the widely observed 5'-dAdoH, and not the less conventional product MTA.
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28
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Wehrspan ZJ, McDonnell RT, Elcock AH. Identification of Iron-Sulfur (Fe-S) Cluster and Zinc (Zn) Binding Sites Within Proteomes Predicted by DeepMind's AlphaFold2 Program Dramatically Expands the Metalloproteome. J Mol Biol 2022; 434:167377. [PMID: 34838520 PMCID: PMC8785651 DOI: 10.1016/j.jmb.2021.167377] [Citation(s) in RCA: 23] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2021] [Revised: 11/17/2021] [Accepted: 11/18/2021] [Indexed: 02/01/2023]
Abstract
DeepMind's AlphaFold2 software has ushered in a revolution in high quality, 3D protein structure prediction. In very recent work by the DeepMind team, structure predictions have been made for entire proteomes of twenty-one organisms, with >360,000 structures made available for download. Here we show that thousands of novel binding sites for iron-sulfur (Fe-S) clusters and zinc (Zn) ions can be identified within these predicted structures by exhaustive enumeration of all potential ligand-binding orientations. We demonstrate that AlphaFold2 routinely makes highly specific predictions of ligand binding sites: for example, binding sites that are comprised exclusively of four cysteine sidechains fall into three clusters, representing binding sites for 4Fe-4S clusters, 2Fe-2S clusters, or individual Zn ions. We show further: (a) that the majority of known Fe-S cluster and Zn binding sites documented in UniProt are recovered by the AlphaFold2 structures, (b) that there are occasional disputes between AlphaFold2 and UniProt with AlphaFold2 predicting highly plausible alternative binding sites, (c) that the Fe-S cluster binding sites that we identify in E. coli agree well with previous bioinformatics predictions, (d) that cysteines predicted here to be part of ligand binding sites show little overlap with those shown via chemoproteomics techniques to be highly reactive, and (e) that AlphaFold2 occasionally appears to build erroneous disulfide bonds between cysteines that should instead coordinate a ligand. These results suggest that AlphaFold2 could be an important tool for the functional annotation of proteomes, and the methodology presented here is likely to be useful for predicting other ligand-binding sites.
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Affiliation(s)
| | | | - Adrian H Elcock
- Department of Biochemistry, University of Iowa, Iowa City, IA, USA.
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29
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Rescuing activity of oxygen-damaged pyruvate formate-lyase by a spare part protein. J Biol Chem 2021; 297:101423. [PMID: 34801558 PMCID: PMC8683613 DOI: 10.1016/j.jbc.2021.101423] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2021] [Revised: 11/09/2021] [Accepted: 11/12/2021] [Indexed: 11/21/2022] Open
Abstract
Pyruvate formate-lyase (PFL) is a glycyl radical enzyme (GRE) that converts pyruvate and coenzyme A into acetyl-CoA and formate in a reaction that is crucial to the primary metabolism of many anaerobic bacteria. The glycyl radical cofactor, which is posttranslationally installed by a radical S-adenosyl-L-methionine (SAM) activase, is a simple and effective catalyst, but is also susceptible to oxidative damage in microaerobic environments. Such damage occurs at the glycyl radical cofactor, resulting in cleaved PFL (cPFL). Bacteria have evolved a spare part protein termed YfiD that can be used to repair cPFL. Previously, we obtained a structure of YfiD by NMR spectroscopy and found that the N-terminus of YfiD was disordered and that the C-terminus of YfiD duplicates the structure of the C-terminus of PFL, including a β-strand that is not removed by the oxygen-induced cleavage. We also showed that cPFL is highly susceptible to proteolysis, suggesting that YfiD rescue of cPFL competes with protein degradation. Here, we probe the mechanism by which YfiD can bind and restore activity to cPFL through enzymatic and spectroscopic studies. Our data show that the disordered N-terminal region of YfiD is important for YfiD glycyl radical installation but not for catalysis, and that the duplicate β-strand does not need to be cleaved from cPFL for YfiD to bind. In fact, truncation of this PFL region prevents YfiD rescue. Collectively our data suggest the molecular mechanisms by which YfiD activation is precluded both when PFL is not damaged and when it is highly damaged.
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30
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Feng JQ, Wang BJ. Super-exchange and exchange-enhanced reactivity in Fe4S4-mediated activation of SAM by radical SAM enzymes. CHINESE J CHEM PHYS 2021. [DOI: 10.1063/1674-0068/cjcp2108134] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Jian-qiang Feng
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Bin-ju Wang
- State Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
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31
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Shepard EM, Impano S, Duffus BR, Pagnier A, Duschene KS, Betz JN, Byer AS, Galambas A, McDaniel EC, Watts H, McGlynn SE, Peters JW, Broderick WE, Broderick JB. HydG, the "dangler" iron, and catalytic production of free CO and CN -: implications for [FeFe]-hydrogenase maturation. Dalton Trans 2021; 50:10405-10422. [PMID: 34240096 PMCID: PMC9154046 DOI: 10.1039/d1dt01359a] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The organometallic H-cluster of the [FeFe]-hydrogenase consists of a [4Fe-4S] cubane bridged via a cysteinyl thiolate to a 2Fe subcluster ([2Fe]H) containing CO, CN-, and dithiomethylamine (DTMA) ligands. The H-cluster is synthesized by three dedicated maturation proteins: the radical SAM enzymes HydE and HydG synthesize the non-protein ligands, while the GTPase HydF serves as a scaffold for assembly of [2Fe]H prior to its delivery to the [FeFe]-hydrogenase containing the [4Fe-4S] cubane. HydG uses l-tyrosine as a substrate, cleaving it to produce p-cresol as well as the CO and CN- ligands to the H-cluster, although there is some question as to whether these are formed as free diatomics or as part of a [Fe(CO)2(CN)] synthon. Here we show that Clostridium acetobutylicum (C.a.) HydG catalyzes formation of multiple equivalents of free CO at rates comparable to those for CN- formation. Free CN- is also formed in excess molar equivalents over protein. A g = 8.9 EPR signal is observed for C.a. HydG reconstituted to load the 5th "dangler" iron of the auxiliary [4Fe-4S][FeCys] cluster and is assigned to this "dangler-loaded" cluster state. Free CO and CN- formation and the degree of activation of [FeFe]-hydrogenase all occur regardless of dangler loading, but are increased 10-35% in the dangler-loaded HydG; this indicates the dangler iron is not essential to this process but may affect relevant catalysis. During HydG turnover in the presence of myoglobin, the g = 8.9 signal remains unchanged, indicating that a [Fe(CO)2(CN)(Cys)] synthon is not formed at the dangler iron. Mutation of the only protein ligand to the dangler iron, H272, to alanine nearly completely abolishes both free CO formation and hydrogenase activation, however results show this is not due solely to the loss of the dangler iron. In experiments with wild type and H272A HydG, and with different degrees of dangler loading, we observe a consistent correlation between free CO/CN- formation and hydrogenase activation. Taken in full, our results point to free CO/CN-, but not an [Fe(CO)2(CN)(Cys)] synthon, as essential species in hydrogenase maturation.
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Affiliation(s)
- Eric M Shepard
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, MT 59717, USA.
| | - Stella Impano
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, MT 59717, USA.
| | - Benjamin R Duffus
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, MT 59717, USA.
| | - Adrien Pagnier
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, MT 59717, USA.
| | - Kaitlin S Duschene
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, MT 59717, USA.
| | - Jeremiah N Betz
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, MT 59717, USA.
| | - Amanda S Byer
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, MT 59717, USA.
| | - Amanda Galambas
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, MT 59717, USA.
| | - Elizabeth C McDaniel
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, MT 59717, USA.
| | - Hope Watts
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, MT 59717, USA.
| | - Shawn E McGlynn
- Earth-Life Science Institute, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152-8550, Japan
| | - John W Peters
- Institute of Biological Chemistry, Washington State University, Pullman, WA 99163, USA
| | - William E Broderick
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, MT 59717, USA.
| | - Joan B Broderick
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, MT 59717, USA.
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32
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Sarkar R, Nandi S, Lo M, Gope A, Chawla-Sarkar M. Viperin, an IFN-Stimulated Protein, Delays Rotavirus Release by Inhibiting Non-Structural Protein 4 (NSP4)-Induced Intrinsic Apoptosis. Viruses 2021; 13:1324. [PMID: 34372530 PMCID: PMC8310278 DOI: 10.3390/v13071324] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2021] [Revised: 06/19/2021] [Accepted: 06/23/2021] [Indexed: 12/27/2022] Open
Abstract
Viral infections lead to expeditious activation of the host's innate immune responses, most importantly the interferon (IFN) response, which manifests a network of interferon-stimulated genes (ISGs) that constrain escalating virus replication by fashioning an ill-disposed environment. Interestingly, most viruses, including rotavirus, have evolved numerous strategies to evade or subvert host immune responses to establish successful infection. Several studies have documented the induction of ISGs during rotavirus infection. In this study, we evaluated the induction and antiviral potential of viperin, an ISG, during rotavirus infection. We observed that rotavirus infection, in a stain independent manner, resulted in progressive upregulation of viperin at increasing time points post-infection. Knockdown of viperin had no significant consequence on the production of total infectious virus particles. Interestingly, substantial escalation in progeny virus release was observed upon viperin knockdown, suggesting the antagonistic role of viperin in rotavirus release. Subsequent studies unveiled that RV-NSP4 triggered relocalization of viperin from the ER, the normal residence of viperin, to mitochondria during infection. Furthermore, mitochondrial translocation of NSP4 was found to be impeded by viperin, leading to abridged cytosolic release of Cyt c and subsequent inhibition of intrinsic apoptosis. Additionally, co-immunoprecipitation studies revealed that viperin associated with NSP4 through regions including both its radical SAM domain and its C-terminal domain. Collectively, the present study demonstrated the role of viperin in restricting rotavirus egress from infected host cells by modulating NSP4 mediated apoptosis, highlighting a novel mechanism behind viperin's antiviral action in addition to the intricacy of viperin-virus interaction.
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Affiliation(s)
| | | | | | | | - Mamta Chawla-Sarkar
- Division of Virology, National Institute of Cholera and Enteric Diseases, P-33, C.I.T. Road Scheme-XM, Beliaghata, Kolkata 700010, India; (R.S.); (S.N.); (M.L.); (A.G.)
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33
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Abstract
![]()
TYW1 is a radical S-adenosyl-l-methionine
(SAM) enzyme that catalyzes the condensation of pyruvate and N-methylguanosine-containing tRNAPhe, forming
4-demethylwyosine-containing tRNAPhe. Homologues of TYW1
are found in both archaea and eukarya; archaeal homologues consist
of a single domain, while eukaryal homologues contain a flavin binding
domain in addition to the radical SAM domain shared with archaeal
homologues. In this study, TYW1 from Saccharomyces cerevisiae (ScTYW1) was heterologously expressed in Escherichia coli and purified to homogeneity. ScTYW1 is purified with 0.54 ± 0.07 and 4.2 ± 1.9 equiv of
flavin mononucleotide (FMN) and iron, respectively, per mole of protein,
suggesting the protein is ∼50% replete with Fe–S clusters
and FMN. While both NADPH and NADH are sufficient for activity, significantly
more product is observed when used in combination with flavin nucleotides. ScTYW1 is the first example of a radical SAM flavoenzyme
that is active with NAD(P)H alone.
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Affiliation(s)
- Anthony P Young
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
| | - Vahe Bandarian
- Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States
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Blue TC, Davis KM. Computational Approaches: An Underutilized Tool in the Quest to Elucidate Radical SAM Dynamics. Molecules 2021; 26:molecules26092590. [PMID: 33946806 PMCID: PMC8124187 DOI: 10.3390/molecules26092590] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 04/22/2021] [Accepted: 04/26/2021] [Indexed: 12/30/2022] Open
Abstract
Enzymes are biological catalysts whose dynamics enable their reactivity. Visualizing conformational changes, in particular, is technically challenging, and little is known about these crucial atomic motions. This is especially problematic for understanding the functional diversity associated with the radical S-adenosyl-L-methionine (SAM) superfamily whose members share a common radical mechanism but ultimately catalyze a broad range of challenging reactions. Computational chemistry approaches provide a readily accessible alternative to exploring the time-resolved behavior of these enzymes that is not limited by experimental logistics. Here, we review the application of molecular docking, molecular dynamics, and density functional theory, as well as hybrid quantum mechanics/molecular mechanics methods to the study of these enzymes, with a focus on understanding the mechanistic dynamics associated with turnover.
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Rupnik K, Rettberg L, Tanifuji K, Rebelein JG, Ribbe MW, Hu Y, Hales BJ. An EPR and VTVH MCD spectroscopic investigation of the nitrogenase assembly protein NifB. J Biol Inorg Chem 2021; 26:403-410. [PMID: 33905031 DOI: 10.1007/s00775-021-01870-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2021] [Accepted: 04/22/2021] [Indexed: 12/01/2022]
Abstract
NifB, a radical SAM enzyme, catalyzes the biosynthesis of the L cluster (Fe8S9C), a structural homolog and precursor to the nitrogenase active-site M cluster ([MoFe7S9C·R-homocitrate]). Sequence analysis shows that NifB contains the CxxCxxxC motif that is typically associated with the radical SAM cluster ([Fe4S4]SAM) involved in the binding of S-adenosylmethionine (SAM). In addition, NifB houses two transient [Fe4S4] clusters (K cluster) that can be fused into an 8Fe L cluster concomitant with the incorporation of an interstitial carbide ion, which is achieved through radical SAM chemistry initiated at the [Fe4S4]SAM cluster upon its interaction with SAM. Here, we report a VTVH MCD/EPR spectroscopic study of the L cluster biosynthesis on NifB, which focuses on the initial interaction of SAM with [Fe4S4]SAM in a variant NifB protein (MaNifBSAM) containing only the [Fe4S4]SAM cluster and no K cluster. Titration of MaNifBSAM with SAM reveals that [Fe4S4]SAM exists in two forms, labeled [Formula: see text] and [Formula: see text]. It is proposed that these forms are involved in the synthesis of the L cluster. Of the two cluster types, only [Formula: see text] initially interacts with SAM, resulting in the generation of Z, an S = ½ paramagnetic [Fe4S4]SAM/SAM complex.
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Affiliation(s)
- Kresimir Rupnik
- Department of Chemistry, Louisiana State University, Baton Rouge, LA, 70803, USA
| | - Lee Rettberg
- Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA, 92697-3900, USA
| | - Kazuki Tanifuji
- Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA, 92697-3900, USA
| | - Johannes G Rebelein
- Max Planck Institute for Terrestrial Microbiology Marburg, Karl-von-Frisch-Strasse 10, 35043, Marburg, Germany
| | - Markus W Ribbe
- Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA, 92697-3900, USA. .,Department of Chemistry, University of California, Irvine, Irvine, CA, 92697-2025, USA.
| | - Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA, 92697-3900, USA.
| | - Brian J Hales
- Department of Chemistry, Louisiana State University, Baton Rouge, LA, 70803, USA.
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Abstract
Sulfonates include diverse natural products and anthropogenic chemicals and are widespread in the environment. Many bacteria can degrade sulfonates and obtain sulfur, carbon, and energy for growth, playing important roles in the biogeochemical sulfur cycle. Cleavage of the inert sulfonate C-S bond involves a variety of enzymes, cofactors, and oxygen-dependent and oxygen-independent catalytic mechanisms. Sulfonate degradation by strictly anaerobic bacteria was recently found to involve C-S bond cleavage through O2-sensitive free radical chemistry, catalyzed by glycyl radical enzymes (GREs). The associated discoveries of new enzymes and metabolic pathways for sulfonate metabolism in diverse anaerobic bacteria have enriched our understanding of sulfonate chemistry in the anaerobic biosphere. An anaerobic environment of particular interest is the human gut microbiome, where sulfonate degradation by sulfate- and sulfite-reducing bacteria (SSRB) produces H2S, a process linked to certain chronic diseases and conditions.
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Affiliation(s)
- Yifeng Wei
- Singapore Institute of Food and Biotechnology Innovation, Agency for Science, Technology and Research (A*STAR), Singapore 138669
| | - Yan Zhang
- Tianjin Key Laboratory for Modern Drug Delivery & High-Efficiency, Collaborative Innovation Center of Chemical Science and Engineering, School of Pharmaceutical Science and Technology; and Frontiers Science Center for Synthetic Biology (Ministry of Education), Tianjin University, Tianjin 300072, China;
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Genome-Driven Discovery of Enzymes with Industrial Implications from the Genus Aneurinibacillus. Microorganisms 2021; 9:microorganisms9030499. [PMID: 33652876 PMCID: PMC7996765 DOI: 10.3390/microorganisms9030499] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Revised: 02/19/2021] [Accepted: 02/23/2021] [Indexed: 01/27/2023] Open
Abstract
Bacteria belonging to the genus Aneurinibacillus within the family Paenibacillaceae are Gram-positive, endospore-forming, and rod-shaped bacteria inhabiting diverse environments. Currently, there are eight validly described species of Aneurinibacillus; however, several unclassified species have also been reported. Aneurinibacillus spp. have shown the potential for producing secondary metabolites (SMs) and demonstrated diverse types of enzyme activities. These features make them promising candidates with industrial implications. At present, genomes of 9 unique species from the genus Aneurinibacillus are available, which can be utilized to decipher invaluable information on their biosynthetic potential as well as enzyme activities. In this work, we performed the comparative genome analyses of nine Aneurinibacillus species representing the first such comprehensive study of this genus at the genome level. We focused on discovering the biosynthetic, biodegradation, and heavy metal resistance potential of this under-investigated genus. The results indicate that the genomes of Aneurinibacillus contain SM-producing regions with diverse bioactivities, including antimicrobial and antiviral activities. Several carbohydrate-active enzymes (CAZymes) and genes involved in heavy metal resistance were also identified. Additionally, a broad range of enzyme classes were also identified in the Aneurinibacillus pan-genomes, making this group of bacteria potential candidates for future investigations with industrial applications.
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Knox HL, Chen PYT, Blaszczyk AJ, Mukherjee A, Grove TL, Schwalm EL, Wang B, Drennan CL, Booker SJ. Structural basis for non-radical catalysis by TsrM, a radical SAM methylase. Nat Chem Biol 2021; 17:485-491. [PMID: 33462497 PMCID: PMC7990684 DOI: 10.1038/s41589-020-00717-y] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2020] [Revised: 11/09/2020] [Accepted: 11/24/2020] [Indexed: 12/19/2022]
Abstract
TsrM methylates C2 of the indole ring of L-tryptophan (Trp) during the biosynthesis of the quinaldic acid moiety of thiostrepton. It is annotated as a cobalamin-dependent radical S-adenosylmethionine (SAM) methylase; however, TsrM does not reductively cleave SAM to the universal 5ʹ-deoxyadenosyl 5ʹ-radical intermediate, a hallmark of radical-SAM (RS) enzymes. Herein, we report structures of TsrM from Kitasatospora setae, the first of a cobalamin-dependent radical SAM methylase. Unexpectedly, the structures show an essential arginine residue that resides in the proximal coordination sphere of the cobalamin cofactor and a [4Fe–4S] cluster that is ligated by a glutamyl residue and three cysteines in a canonical CxxxCxxC RS motif. Structures in the presence of substrates suggest a substrate-assisted mechanism of catalysis, wherein the carboxylate group of SAM serves as a general base to deprotonate N1 of the tryptophan substrate, facilitating formation of a C2 carbanion. The first crystal structures of a cobalamin-dependent radical SAM methylase reveal an unexpected mode of methylation.
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Affiliation(s)
- Hayley L Knox
- Department of Chemistry, Pennsylvania State University, University Park, PA, USA
| | - Percival Yang-Ting Chen
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA.,Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, USA
| | - Anthony J Blaszczyk
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, PA, USA.,Catalent Pharma Solutions, Gaithersburg, MD, USA
| | - Arnab Mukherjee
- Department of Chemistry, Pennsylvania State University, University Park, PA, USA
| | - Tyler L Grove
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY, USA
| | - Erica L Schwalm
- Department of Chemistry, Pennsylvania State University, University Park, PA, USA.,Merck & Co., Inc., Rahway, NJ, USA
| | - Bo Wang
- Department of Chemistry, Pennsylvania State University, University Park, PA, USA
| | - Catherine L Drennan
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, USA. .,Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, USA. .,Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA, USA.
| | - Squire J Booker
- Department of Chemistry, Pennsylvania State University, University Park, PA, USA. .,Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, PA, USA. .,Howard Hughes Medical Institute, Pennsylvania State University, University Park, PA, USA.
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39
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Impano S, Yang H, Jodts RJ, Pagnier A, Swimley R, McDaniel EC, Shepard EM, Broderick WE, Broderick JB, Hoffman BM. Active-Site Controlled, Jahn-Teller Enabled Regioselectivity in Reductive S-C Bond Cleavage of S-Adenosylmethionine in Radical SAM Enzymes. J Am Chem Soc 2021; 143:335-348. [PMID: 33372786 PMCID: PMC7934139 DOI: 10.1021/jacs.0c10925] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Catalysis by canonical radical S-adenosyl-l-methionine (SAM) enzymes involves electron transfer (ET) from [4Fe-4S]+ to SAM, generating an R3S0 radical that undergoes regioselective homolytic reductive cleavage of the S-C5' bond to generate the 5'-dAdo· radical. However, cryogenic photoinduced S-C bond cleavage has regioselectively yielded either 5'-dAdo· or ·CH3, and indeed, each of the three SAM S-C bonds can be regioselectively cleaved in an RS enzyme. This diversity highlights a longstanding central question: what controls regioselective homolytic S-C bond cleavage upon SAM reduction? We here provide an unexpected answer, founded on our observation that photoinduced S-C bond cleavage in multiple canonical RS enzymes reveals two enzyme classes: in one, photolysis forms 5'-dAdo·, and in another it forms ·CH3. The identity of the cleaved S-C bond correlates with SAM ribose conformation but not with positioning and orientation of the sulfonium center relative to the [4Fe-4S] cluster. We have recognized the reduced-SAM R3S0 radical is a (2E) state with its antibonding unpaired electron in an orbital doublet, which renders R3S0 Jahn-Teller (JT)-active and therefore subject to vibronically induced distortion. Active-site forces induce a JT distortion that localizes the odd electron in a single priority S-C antibond, which undergoes regioselective cleavage. In photolytic cleavage those forces act through control of the ribose conformation and are transmitted to the sulfur via the S-C5' bond, but during catalysis thermally induced conformational changes that enable ET from a cluster iron generate dominant additional forces that specifically select S-C5' for cleavage. This motion also can explain how 5'-dAdo· subsequently forms the organometallic intermediate Ω.
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Affiliation(s)
- Stella Impano
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Hao Yang
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Richard J Jodts
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Adrien Pagnier
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Ryan Swimley
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Elizabeth C McDaniel
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Eric M Shepard
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - William E Broderick
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Joan B Broderick
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Brian M Hoffman
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
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40
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Kang W, Rettberg LA, Stiebritz MT, Jasniewski AJ, Tanifuji K, Lee CC, Ribbe MW, Hu Y. X‐Ray Crystallographic Analysis of NifB with a Full Complement of Clusters: Structural Insights into the Radical SAM‐Dependent Carbide Insertion During Nitrogenase Cofactor Assembly. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202011367] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Wonchull Kang
- Department of Molecular Biology & Biochemistry University of California, Irvine Irvine CA 92697-3900 USA
| | - Lee A. Rettberg
- Department of Molecular Biology & Biochemistry University of California, Irvine Irvine CA 92697-3900 USA
| | - Martin T. Stiebritz
- Department of Molecular Biology & Biochemistry University of California, Irvine Irvine CA 92697-3900 USA
| | - Andrew J. Jasniewski
- Department of Molecular Biology & Biochemistry University of California, Irvine Irvine CA 92697-3900 USA
| | - Kazuki Tanifuji
- Department of Molecular Biology & Biochemistry University of California, Irvine Irvine CA 92697-3900 USA
| | - Chi Chung Lee
- Department of Molecular Biology & Biochemistry University of California, Irvine Irvine CA 92697-3900 USA
| | - Markus W. Ribbe
- Department of Molecular Biology & Biochemistry University of California, Irvine Irvine CA 92697-3900 USA
- Department of Chemistry University of California, Irvine Irvine CA 92697-2025 USA
| | - Yilin Hu
- Department of Molecular Biology & Biochemistry University of California, Irvine Irvine CA 92697-3900 USA
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41
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Kang W, Rettberg LA, Stiebritz MT, Jasniewski AJ, Tanifuji K, Lee CC, Ribbe MW, Hu Y. X-Ray Crystallographic Analysis of NifB with a Full Complement of Clusters: Structural Insights into the Radical SAM-Dependent Carbide Insertion During Nitrogenase Cofactor Assembly. Angew Chem Int Ed Engl 2020; 60:2364-2370. [PMID: 33035363 DOI: 10.1002/anie.202011367] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2020] [Revised: 09/27/2020] [Indexed: 12/13/2022]
Abstract
NifB is an essential radical SAM enzyme required for the assembly of an 8Fe core of the nitrogenase cofactor. Herein, we report the X-ray crystal structures of Methanobacterium thermoautotrophicum NifB without (apo MtNifB) and with (holo MtNifB) a full complement of three [Fe4 S4 ] clusters. Both apo and holo MtNifB contain a partial TIM barrel core, but unlike apo MtNifB, holo MtNifB is fully assembled and competent in cofactor biosynthesis. The radical SAM (RS)-cluster is coordinated by three Cys, and the adjacent K1- and K2-clusters, representing the precursor to an 8Fe cofactor core, are each coordinated by one His and two Cys. Prediction of substrate channels, combined with in silico docking of SAM in holo MtNifB, suggests the binding of SAM between the RS- and K2-clusters and putative paths for entry of SAM and exit of products of SAM cleavage, thereby providing important mechanistic insights into the radical SAM-dependent carbide insertion concomitant with cofactor core formation.
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Affiliation(s)
- Wonchull Kang
- Department of Molecular Biology & Biochemistry, University of California, Irvine, Irvine, CA, 92697-3900, USA
| | - Lee A Rettberg
- Department of Molecular Biology & Biochemistry, University of California, Irvine, Irvine, CA, 92697-3900, USA
| | - Martin T Stiebritz
- Department of Molecular Biology & Biochemistry, University of California, Irvine, Irvine, CA, 92697-3900, USA
| | - Andrew J Jasniewski
- Department of Molecular Biology & Biochemistry, University of California, Irvine, Irvine, CA, 92697-3900, USA
| | - Kazuki Tanifuji
- Department of Molecular Biology & Biochemistry, University of California, Irvine, Irvine, CA, 92697-3900, USA
| | - Chi Chung Lee
- Department of Molecular Biology & Biochemistry, University of California, Irvine, Irvine, CA, 92697-3900, USA
| | - Markus W Ribbe
- Department of Molecular Biology & Biochemistry, University of California, Irvine, Irvine, CA, 92697-3900, USA.,Department of Chemistry, University of California, Irvine, Irvine, CA, 92697-2025, USA
| | - Yilin Hu
- Department of Molecular Biology & Biochemistry, University of California, Irvine, Irvine, CA, 92697-3900, USA
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42
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Bím D, Alonso-Gil S, Srnec M. From Synthetic to Biological Fe 4 S 4 Complexes: Redox Properties Correlated to Function of Radical S-Adenosylmethionine Enzymes. Chempluschem 2020; 85:2534-2541. [PMID: 33245201 DOI: 10.1002/cplu.202000663] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Revised: 11/02/2020] [Indexed: 11/10/2022]
Abstract
By employing the computational protocol for calculation of reduction potentials of the Fe4 S4 -containing species validated using a representative series of well-defined synthetic complexes, we focused on redox properties of two prototypical radical SAM enzymes to reveal how they transform SAM into the reactive 5'-deoxyadenosyl radical, and how they tune this radical for its proper biological function. We found the reduction potential of SAM is indeed elevated by 0.3-0.4 V upon coordination to Fe4 S4 , which was previously speculated in the literature. This makes a generation of 5'-deoxyadenosyl radical from SAM less endergonic (by ca. 7-9 kcal mol-1 ) and hence more feasible in both enzymes as compared to the identical process in water. Furthermore, our calculations indicate that the enzyme-bound 5'-deoxyadenosyl radical has a significantly lower reduction potential than in referential aqueous solution, which may help the enzymes to suppress potential side redox reactions and simultaneously elevate its proton-philic character, which may, in turn, promote the radical hydrogen-atom abstraction ability.
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Affiliation(s)
- Daniel Bím
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, Prague, 8 182 23, Czech Republic
| | - Santiago Alonso-Gil
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, Prague, 8 182 23, Czech Republic
| | - Martin Srnec
- J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, Dolejškova 3, Prague, 8 182 23, Czech Republic
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43
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Zhao C, Li Y, Wang C, Chen H. Mechanistic Dichotomy in the Activation of SAM by Radical SAM Enzymes: QM/MM Modeling Deciphers the Determinant. ACS Catal 2020. [DOI: 10.1021/acscatal.0c03384] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Chengxin Zhao
- Beijing National Laboratory for Molecular Sciences (BNLMS), CAS Key Laboratory of Photochemistry, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yao Li
- Beijing National Laboratory for Molecular Sciences (BNLMS), CAS Key Laboratory of Photochemistry, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Chao Wang
- Beijing National Laboratory for Molecular Sciences (BNLMS), CAS Key Laboratory of Photochemistry, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Hui Chen
- Beijing National Laboratory for Molecular Sciences (BNLMS), CAS Key Laboratory of Photochemistry, CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
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44
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Pagnier A, Yang H, Jodts RJ, James CD, Shepard EM, Impano S, Broderick WE, Hoffman BM, Broderick JB. Radical SAM Enzyme Spore Photoproduct Lyase: Properties of the Ω Organometallic Intermediate and Identification of Stable Protein Radicals Formed during Substrate-Free Turnover. J Am Chem Soc 2020; 142:18652-18660. [PMID: 32966073 DOI: 10.1021/jacs.0c08585] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Spore photoproduct lyase is a radical S-adenosyl-l-methionine (SAM) enzyme with the unusual property that addition of SAM to the [4Fe-4S]1+ enzyme absent substrate results in rapid electron transfer to SAM with accompanying homolytic S-C5' bond cleavage. Herein, we demonstrate that this unusual reaction forms the organometallic intermediate Ω in which the unique Fe atom of the [4Fe-4S] cluster is bound to C5' of the 5'-deoxyadenosyl radical (5'-dAdo•). During catalysis, homolytic cleavage of the Fe-C5' bond liberates 5'-dAdo• for reaction with substrate, but here, we use Ω formation without substrate to determine the thermal stability of Ω. The reaction of Geobacillus thermodenitrificans SPL (GtSPL) with SAM forms Ω within ∼15 ms after mixing. By monitoring the decay of Ω through rapid freeze-quench trapping at progressively longer times we find an ambient temperature decay time of the Ω Fe-C5' bond of τ ≈ 5-6 s, likely shortened by enzymatic activation as is the case with the Co-C5' bond of B12. We have further used hand quenching at times up to 10 min, and thus with multiple SAM turnovers, to probe the fate of the 5'-dAdo• radical liberated by Ω. In the absence of substrate, Ω undergoes low-probability conversion to a stable protein radical. The WT enzyme with valine at residue 172 accumulates a Val•; mutation of Val172 to isoleucine or cysteine results in accumulation of an Ile• or Cys• radical, respectively. The structures of the radical in WT, V172I, and V172C variants have been established by detailed EPR/DFT analyses.
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Affiliation(s)
- Adrien Pagnier
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, Montana. 59717, United States
| | - Hao Yang
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Richard J Jodts
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Christopher D James
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Eric M Shepard
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, Montana. 59717, United States
| | - Stella Impano
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, Montana. 59717, United States
| | - William E Broderick
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, Montana. 59717, United States
| | - Brian M Hoffman
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Joan B Broderick
- Department of Chemistry & Biochemistry, Montana State University, Bozeman, Montana. 59717, United States
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45
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Two radical-dependent mechanisms for anaerobic degradation of the globally abundant organosulfur compound dihydroxypropanesulfonate. Proc Natl Acad Sci U S A 2020; 117:15599-15608. [PMID: 32571930 DOI: 10.1073/pnas.2003434117] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
2(S)-dihydroxypropanesulfonate (DHPS) is a microbial degradation product of 6-deoxy-6-sulfo-d-glucopyranose (sulfoquinovose), a component of plant sulfolipid with an estimated annual production of 1010 tons. DHPS is also at millimolar levels in highly abundant marine phytoplankton. Its degradation and sulfur recycling by microbes, thus, play important roles in the biogeochemical sulfur cycle. However, DHPS degradative pathways in the anaerobic biosphere are not well understood. Here, we report the discovery and characterization of two O2-sensitive glycyl radical enzymes that use distinct mechanisms for DHPS degradation. DHPS-sulfolyase (HpsG) in sulfate- and sulfite-reducing bacteria catalyzes C-S cleavage to release sulfite for use as a terminal electron acceptor in respiration, producing H2S. DHPS-dehydratase (HpfG), in fermenting bacteria, catalyzes C-O cleavage to generate 3-sulfopropionaldehyde, subsequently reduced by the NADH-dependent sulfopropionaldehyde reductase (HpfD). Both enzymes are present in bacteria from diverse environments including human gut, suggesting the contribution of enzymatic radical chemistry to sulfur flux in various anaerobic niches.
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46
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Fajardo AS, Legrand P, Payá-Tormo LA, Martin L, Pellicer Martı Nez MT, Echavarri-Erasun C, Vernède X, Rubio LM, Nicolet Y. Structural Insights into the Mechanism of the Radical SAM Carbide Synthase NifB, a Key Nitrogenase Cofactor Maturating Enzyme. J Am Chem Soc 2020; 142:11006-11012. [PMID: 32476412 DOI: 10.1021/jacs.0c02243] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Nitrogenase is a key player in the global nitrogen cycle, as it catalyzes the reduction of dinitrogen into ammonia. The active site of the nitrogenase MoFe protein corresponds to a [MoFe7S9C-(R)-homocitrate] species designated FeMo-cofactor, whose biosynthesis and insertion requires the action of over a dozen maturation proteins provided by the NIF (for NItrogen Fixation) assembly machinery. Among them, the radical SAM protein NifB plays an essential role, concomitantly inserting a carbide ion and coupling two [Fe4S4] clusters to form a [Fe8S9C] precursor called NifB-co. Here we report on the X-ray structure of NifB from Methanotrix thermoacetophila at 1.95 Å resolution in a state pending the binding of one [Fe4S4] cluster substrate. The overall NifB architecture indicates that this enzyme has a single SAM binding site, which at this stage is occupied by cysteine residue 62. The structure reveals a unique ligand binding mode for the K1-cluster involving cysteine residues 29 and 128 in addition to histidine 42 and glutamate 65. The latter, together with cysteine 62, belongs to a loop inserted in the active site, likely protecting the already present [Fe4S4] clusters. These two residues regulate the sequence of events, controlling SAM dual reactivity and preventing unwanted radical-based chemistry before the K2 [Fe4S4] cluster substrate is loaded into the protein. The location of the K1-cluster, too far away from the SAM binding site, supports a mechanism in which the K2-cluster is the site of methylation.
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Affiliation(s)
- Ana Sosa Fajardo
- Centro de Biotecnologı́a y Genómica de Plantas, Universidad Politécnica de Madrid, Instituto Nacional de Investigación y Tecnologı́a Agraria y Alimentaria, Pozuelo de Alarcón, 28223 Madrid, Spain.,Univ. Grenoble Alpes, CEA, CNRS, IBS, Metalloproteins Unit, F-38000 Grenoble, France
| | - Pierre Legrand
- Synchrotron SOLEIL, L'Orme des Merisiers, Gif-sur-Yvette, France
| | - Lucı A Payá-Tormo
- Centro de Biotecnologı́a y Genómica de Plantas, Universidad Politécnica de Madrid, Instituto Nacional de Investigación y Tecnologı́a Agraria y Alimentaria, Pozuelo de Alarcón, 28223 Madrid, Spain.,Departamento de Biotecnologı́a-Biología Vegetal, Escuela Técnica Superior de Ingenierı́a Agronómica, Alimentarı́a y de Biosistemas, Universidad Politécnica de Madrid, 28040 Madrid, Spain
| | - Lydie Martin
- Univ. Grenoble Alpes, CEA, CNRS, IBS, Metalloproteins Unit, F-38000 Grenoble, France
| | - Maria Teresa Pellicer Martı Nez
- Centro de Biotecnologı́a y Genómica de Plantas, Universidad Politécnica de Madrid, Instituto Nacional de Investigación y Tecnologı́a Agraria y Alimentaria, Pozuelo de Alarcón, 28223 Madrid, Spain
| | - Carlos Echavarri-Erasun
- Centro de Biotecnologı́a y Genómica de Plantas, Universidad Politécnica de Madrid, Instituto Nacional de Investigación y Tecnologı́a Agraria y Alimentaria, Pozuelo de Alarcón, 28223 Madrid, Spain.,Departamento de Biotecnologı́a-Biología Vegetal, Escuela Técnica Superior de Ingenierı́a Agronómica, Alimentarı́a y de Biosistemas, Universidad Politécnica de Madrid, 28040 Madrid, Spain
| | - Xavier Vernède
- Univ. Grenoble Alpes, CEA, CNRS, IBS, Metalloproteins Unit, F-38000 Grenoble, France
| | - Luis M Rubio
- Centro de Biotecnologı́a y Genómica de Plantas, Universidad Politécnica de Madrid, Instituto Nacional de Investigación y Tecnologı́a Agraria y Alimentaria, Pozuelo de Alarcón, 28223 Madrid, Spain.,Departamento de Biotecnologı́a-Biología Vegetal, Escuela Técnica Superior de Ingenierı́a Agronómica, Alimentarı́a y de Biosistemas, Universidad Politécnica de Madrid, 28040 Madrid, Spain
| | - Yvain Nicolet
- Univ. Grenoble Alpes, CEA, CNRS, IBS, Metalloproteins Unit, F-38000 Grenoble, France
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47
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Pang H, Lilla EA, Zhang P, Zhang D, Shields TP, Scott LG, Yang W, Yokoyama K. Mechanism of Rate Acceleration of Radical C-C Bond Formation Reaction by a Radical SAM GTP 3',8-Cyclase. J Am Chem Soc 2020; 142:9314-9326. [PMID: 32348669 DOI: 10.1021/jacs.0c01200] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
While the number of characterized radical S-adenosyl-l-methionine (SAM) enzymes is increasing, the roles of these enzymes in radical catalysis remain largely ambiguous. In radical SAM enzymes, the slow radical initiation step kinetically masks the subsequent steps, making it impossible to study the kinetics of radical chemistry. Due to this kinetic masking, it is unknown whether the subsequent radical reactions require rate acceleration by the enzyme active site. Here, we report the first evidence that a radical SAM enzyme MoaA accelerates the radical-mediated C-C bond formation. MoaA catalyzes an unprecedented 3',8-cyclization of GTP into 3',8-cyclo-7,8-dihydro-GTP (3',8-cH2GTP) during the molybdenum cofactor (Moco) biosynthesis. Through a series of EPR and biochemical characterizations, we found that MoaA catalyzes a shunt pathway in which an on-pathway intermediate, GTP C-3' radical, abstracts H-4' atom from (4'R)-5'-deoxyadenosine (5'-dA) to transiently generate 5'-deoxyadenos-4'-yl radical (5'-dA-C4'•) that is subsequently reduced stereospecifically to yield (4'S)-5'-dA. Detailed kinetic characterization of the shunt and the main pathways provided the comprehensive view of MoaA kinetics and determined the rate of the on-pathway 3',8-cyclization step as 2.7 ± 0.7 s-1. Together with DFT calculations, this observation suggested that the 3',8-cyclization by MoaA is accelerated by 6-9 orders of magnitude. Further experimental and theoretical characterizations suggested that the rate acceleration is achieved mainly by constraining the triphosphate and guanine base positions while leaving the ribose flexible, and a transition state stabilization through H-bond and electrostatic interactions with the positively charged R17 residue. This is the first evidence for rate acceleration of radical reactions by a radical SAM enzyme and provides insights into the mechanism by which radical SAM enzymes accelerate radical chemistry.
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Affiliation(s)
- Haoran Pang
- Department of Biochemistry, Duke University School of Medicine, Durham, North Carolina 27710, United States
| | - Edward A Lilla
- Department of Biochemistry, Duke University School of Medicine, Durham, North Carolina 27710, United States
| | - Pan Zhang
- Department of Chemistry, Duke University, Durham, North Carolina 27710, United States
| | - Du Zhang
- Department of Chemistry, Duke University, Durham, North Carolina 27710, United States
| | - Thomas P Shields
- Cassia, LLC, 3030 Bunker Hill Street, Suite 214, San Diego, California 92109, United States
| | - Lincoln G Scott
- Cassia, LLC, 3030 Bunker Hill Street, Suite 214, San Diego, California 92109, United States
| | - Weitao Yang
- Department of Chemistry, Duke University, Durham, North Carolina 27710, United States
| | - Kenichi Yokoyama
- Department of Biochemistry, Duke University School of Medicine, Durham, North Carolina 27710, United States.,Department of Chemistry, Duke University, Durham, North Carolina 27710, United States
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48
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49
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Backman LRF, Huang YY, Andorfer MC, Gold B, Raines RT, Balskus EP, Drennan CL. Molecular basis for catabolism of the abundant metabolite trans-4-hydroxy-L-proline by a microbial glycyl radical enzyme. eLife 2020; 9:e51420. [PMID: 32180548 PMCID: PMC7077986 DOI: 10.7554/elife.51420] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2019] [Accepted: 02/19/2020] [Indexed: 02/04/2023] Open
Abstract
The glycyl radical enzyme (GRE) superfamily utilizes a glycyl radical cofactor to catalyze difficult chemical reactions in a variety of anaerobic microbial metabolic pathways. Recently, a GRE, trans-4-hydroxy-L-proline (Hyp) dehydratase (HypD), was discovered that catalyzes the dehydration of Hyp to (S)-Δ1-pyrroline-5-carboxylic acid (P5C). This enzyme is abundant in the human gut microbiome and also present in prominent bacterial pathogens. However, we lack an understanding of how HypD performs its unusual chemistry. Here, we have solved the crystal structure of HypD from the pathogen Clostridioides difficile with Hyp bound in the active site. Biochemical studies have led to the identification of key catalytic residues and have provided insight into the radical mechanism of Hyp dehydration.
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Affiliation(s)
- Lindsey RF Backman
- Department of Chemistry, Massachusetts Institute of TechnologyCambridgeUnited States
| | - Yolanda Y Huang
- Department of Chemistry and Chemical Biology, Harvard UniversityCambridgeUnited States
| | - Mary C Andorfer
- Department of Biology, Massachusetts Institute of TechnologyCambridgeUnited States
| | - Brian Gold
- Department of Chemistry, Massachusetts Institute of TechnologyCambridgeUnited States
| | - Ronald T Raines
- Department of Chemistry, Massachusetts Institute of TechnologyCambridgeUnited States
| | - Emily P Balskus
- Department of Chemistry and Chemical Biology, Harvard UniversityCambridgeUnited States
| | - Catherine L Drennan
- Department of Chemistry, Massachusetts Institute of TechnologyCambridgeUnited States
- Department of Biology, Massachusetts Institute of TechnologyCambridgeUnited States
- Howard Hughes Medical Institute, Massachusetts Institute of TechnologyCambridgeUnited States
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Yang H, Impano S, Shepard EM, James CD, Broderick WE, Broderick JB, Hoffman BM. Photoinduced Electron Transfer in a Radical SAM Enzyme Generates an S-Adenosylmethionine Derived Methyl Radical. J Am Chem Soc 2019; 141:16117-16124. [PMID: 31509404 DOI: 10.1021/jacs.9b08541] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Radical SAM (RS) enzymes use S-adenosyl-l-methionine (SAM) and a [4Fe-4S] cluster to initiate a broad spectrum of radical transformations throughout all kingdoms of life. We report here that low-temperature photoinduced electron transfer from the [4Fe-4S]1+ cluster to bound SAM in the active site of the hydrogenase maturase RS enzyme, HydG, results in specific homolytic cleavage of the S-CH3 bond of SAM, rather than the S-C5' bond as in the enzyme-catalyzed (thermal) HydG reaction. This result is in stark contrast to a recent report in which photoinduced ET in the RS enzyme pyruvate formate-lyase activating enzyme cleaved the S-C5' bond to generate a 5'-deoxyadenosyl radical, and provides the first direct evidence for homolytic S-CH3 bond cleavage in a RS enzyme. Photoinduced ET in HydG generates a trapped •CH3 radical, as well as a small population of an organometallic species with an Fe-CH3 bond, denoted ΩM. The •CH3 radical is surprisingly found to exhibit rotational diffusion in the HydG active site at temperatures as low as 40 K, and is rapidly quenched: whereas 5'-dAdo• is stable indefinitely at 77 K, •CH3 quenches with a half-time of ∼2 min at this temperature. The rapid quenching and rotational/translational freedom of •CH3 shows that enzymes would be unable to harness this radical as a regio- and stereospecific H atom abstractor during catalysis, in contrast to the exquisite control achieved with the enzymatically generated 5'-dAdo•.
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Affiliation(s)
- Hao Yang
- Department of Chemistry , Northwestern University , Evanston , Illinois 60208 , United States
| | - Stella Impano
- Department of Chemistry & Biochemistry , Montana State University , Bozeman , Montana 59717 , United States
| | - Eric M Shepard
- Department of Chemistry & Biochemistry , Montana State University , Bozeman , Montana 59717 , United States
| | - Christopher D James
- Department of Chemistry , Northwestern University , Evanston , Illinois 60208 , United States
| | - William E Broderick
- Department of Chemistry & Biochemistry , Montana State University , Bozeman , Montana 59717 , United States
| | - Joan B Broderick
- Department of Chemistry & Biochemistry , Montana State University , Bozeman , Montana 59717 , United States
| | - Brian M Hoffman
- Department of Chemistry , Northwestern University , Evanston , Illinois 60208 , United States
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