1
|
Groves JT, Feng L, Austin RN. Structure and Function of Alkane Monooxygenase (AlkB). Acc Chem Res 2023; 56:3665-3675. [PMID: 38032826 DOI: 10.1021/acs.accounts.3c00590] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2023]
Abstract
Every year, perhaps as much as 800 million tons of hydrocarbons enters the environment; alkanes make up a large percentage of it. Most are transformed by organisms that utilize these molecules as sources of energy and carbon. Both aerobic and anaerobic alkane transformation chemistries exist, capitalizing on the presence of alkanes in both oxic and anoxic environments. Over the past 40 years, tremendous progress has been made in understanding the structure and mechanism of enzymes that catalyze the transformation of methane. By contrast, progress involving enzymes that transform liquid alkanes has been slower with the first structures of AlkB, the predominant aerobic alkane hydroxylase in the environment, appearing in 2023. Because of the fundamental importance of C-H bond activation chemistries, interest in understanding how biology activates and transforms alkanes is high.In this Account, we focus on steps we have taken to understand the mechanism and structure of alkane monooxygenase (AlkB), the metalloenzyme that dominates the transformation of liquid alkanes in the environment (not to be confused with another AlkB that is an α-ketogluturate-dependent enzyme involved in DNA repair). First, we briefly describe what is known about the prevalence of AlkB in the environment and its role in the carbon cycle. Then we review the key findings from our recent high-resolution cryoEM structure of AlkB and highlight important similarities and differences in the structures of members of class III diiron enzymes. Functional studies, which we summarize, from a number of single residue variants enable us to say a great deal about how the structure of AlkB facilitates its function. Next, we overview work from our laboratories using mechanistically diagnostic radical clock substrates to characterize the mechanism of AlkB and contextualize the results we have obtained on AlkB with results we have obtained on other alkane-oxidizing enzymes and explain these results in light of the enzyme's structure. Finally, we integrate recent work in our laboratories with information from prior studies of AlkB, and relevant model systems, to create a holistic picture of the enzyme. We end by pointing to critical questions that still need to be answered, questions about the electronic structure of the active site of the enzyme throughout the reaction cycle and about whether and to what extent the enzyme plays functional roles in biology beyond simply initiating the degradation of alkanes.
Collapse
Affiliation(s)
- John T Groves
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
| | - Liang Feng
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, California 94305, United States
| | | |
Collapse
|
2
|
Fenibo EO, Selvarajan R, Abia ALK, Matambo T. Medium-chain alkane biodegradation and its link to some unifying attributes of alkB genes diversity. THE SCIENCE OF THE TOTAL ENVIRONMENT 2023; 877:162951. [PMID: 36948313 DOI: 10.1016/j.scitotenv.2023.162951] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Revised: 03/14/2023] [Accepted: 03/15/2023] [Indexed: 05/06/2023]
Abstract
Hydrocarbon footprints in the environment, via biosynthesis, natural seepage, anthropogenic activities and accidents, affect the ecosystem and induce a shift in the healthy biogeochemical equilibrium that drives needed ecological services. In addition, these imbalances cause human diseases and reduce animal and microorganism diversity. Microbial bioremediation, which capitalizes on functional genes, is a sustainable mitigation option for cleaning hydrocarbon-impacted environments. This review focuses on the bacterial alkB functional gene, which codes for a non-heme di‑iron monooxygenase (AlkB) with a di‑iron active site that catalyzes C8-C16 medium-chain alkane metabolism. These enzymes are ubiquitous and share common attributes such as being controlled by global transcriptional regulators, being a component of most super hydrocarbon degraders, and their distributions linked to horizontal gene transfer (HGT) events. The phylogenetic approach used in the HGT detection suggests that AlkB tree topology clusters bacteria functionally and that a preferential gradient dictates gene distribution. The alkB gene also acts as a biomarker for bioremediation, although it is found in pristine environments and absent in some hydrocarbon degraders. For instance, a quantitative molecular method has failed to link alkB copy number to contamination concentration levels. This limitation may be due to AlkB homologues, which have other functions besides n-alkane assimilation. Thus, this review, which focuses on Pseudomonas putida GPo1 alkB, shows that AlkB proteins are diverse but have some unifying trends around hydrocarbon-degrading bacteria; it is erroneous to rely on alkB detection alone as a monitoring parameter for hydrocarbon degradation, alkB gene distribution are preferentially distributed among bacteria, and the plausible explanation for AlkB affiliation to broad-spectrum metabolism of hydrocarbons in super-degraders hitherto reported. Overall, this review provides a broad perspective of the ecology of alkB-carrying bacteria and their directed biodegradation pathways.
Collapse
Affiliation(s)
- Emmanuel Oliver Fenibo
- World Bank Africa Centre of Excellence, Centre for Oilfield Chemical Research, University of Port Harcourt, Port Harcourt 500272, Nigeria
| | - Ramganesh Selvarajan
- Laboratory of Extraterrestrial Ocean Systems (LEOS), Institute of Deep-Sea Science and Engineering, Chinese Academy of Sciences, Sanya, China; Department of Environmental Science, University of South Africa, Florida Campus, 1710, South Africa
| | - Akebe Luther King Abia
- Department of Environmental Science, University of South Africa, Florida Campus, 1710, South Africa; Environmental Research Foundation, Westville 3630, South Africa
| | - Tonderayi Matambo
- Institute for the Development of Energy for African Sustainability, University of South Africa, Roodepoort 1709, South Africa.
| |
Collapse
|
3
|
Guo X, Zhang J, Han L, Lee J, Williams SC, Forsberg A, Xu Y, Austin RN, Feng L. Structure and mechanism of the alkane-oxidizing enzyme AlkB. Nat Commun 2023; 14:2180. [PMID: 37069165 PMCID: PMC10110569 DOI: 10.1038/s41467-023-37869-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Accepted: 04/03/2023] [Indexed: 04/19/2023] Open
Abstract
Alkanes are the most energy-rich form of carbon and are widely dispersed in the environment. Their transformation by microbes represents a key step in the global carbon cycle. Alkane monooxygenase (AlkB), a membrane-spanning metalloenzyme, converts straight chain alkanes to alcohols in the first step of the microbially-mediated degradation of alkanes, thereby playing a critical role in the global cycling of carbon and the bioremediation of oil. AlkB biodiversity is attributed to its ability to oxidize alkanes of various chain lengths, while individual AlkBs target a relatively narrow range. Mechanisms of substrate selectivity and catalytic activity remain elusive. Here we report the cryo-EM structure of AlkB, which provides a distinct architecture for membrane enzymes. Our structure and functional studies reveal an unexpected diiron center configuration and identify molecular determinants for substrate selectivity. These findings provide insight into the catalytic mechanism of AlkB and shed light on its function in alkane-degrading microorganisms.
Collapse
Affiliation(s)
- Xue Guo
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Jianxiu Zhang
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Lei Han
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Juliet Lee
- Department of Chemistry, Barnard College, 3009 Broadway, New York, NY, 10027, USA
- Department of Biochemistry and Molecular Biophysics, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Shoshana C Williams
- Department of Chemistry, Barnard College, 3009 Broadway, New York, NY, 10027, USA
- Department of Chemistry, Stanford University, Stanford, CA, 94305, USA
| | - Allison Forsberg
- Department of Chemistry, Barnard College, 3009 Broadway, New York, NY, 10027, USA
- Department of Chemistry, University of Southern California, Los Angeles, CA, 90007, USA
| | - Yan Xu
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | | | - Liang Feng
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, 94305, USA.
| |
Collapse
|
4
|
Omura K, Aiba Y, Suzuki K, Ariyasu S, Sugimoto H, Shoji O. A P450 Harboring Manganese Protoporphyrin IX Generates a Manganese Analogue of Compound I by Activating Dioxygen. ACS Catal 2022. [DOI: 10.1021/acscatal.2c01345] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Keita Omura
- Department of Chemistry, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Yuichiro Aiba
- Department of Chemistry, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Kazuto Suzuki
- Department of Chemistry, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Shinya Ariyasu
- Department of Chemistry, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Hiroshi Sugimoto
- RIKEN SPring-8 Center, Harima Institute, 1-1-1 Kouto, Sayo, Hyogo 679-5148, Japan
- Core Research for Evolutional Science and Technology (Japan), Science and Technology Agency, 5 Sanbancho, Chiyoda-ku, Tokyo 102-0075, Japan
| | - Osami Shoji
- Department of Chemistry, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
- Core Research for Evolutional Science and Technology (Japan), Science and Technology Agency, 5 Sanbancho, Chiyoda-ku, Tokyo 102-0075, Japan
| |
Collapse
|
5
|
Williams SC, Luongo D, Orman M, Vizcarra CL, Austin RN. An alkane monooxygenase (AlkB) family in which all electron transfer partners are covalently bound to the oxygen-activating hydroxylase. J Inorg Biochem 2022; 228:111707. [PMID: 34990970 PMCID: PMC8799515 DOI: 10.1016/j.jinorgbio.2021.111707] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Revised: 12/13/2021] [Accepted: 12/29/2021] [Indexed: 10/19/2022]
Abstract
Alkane monooxygenase (AlkB) is a non-heme diiron enzyme that catalyzes the hydroxylation of alkanes. It is commonly found in alkanotrophic organisms that can live on alkanes as their sole source of carbon and energy. Activation of AlkB occurs via two-electron reduction of its diferric active site, which facilitates the binding, activation, and cleavage of molecular oxygen for insertion into an inert CH bond. Electrons are typically supplied by NADH via a rubredoxin reductase (AlkT) to a rubredoxin (AlkG) to AlkB, although alternative electron transfer partners have been observed. Here we report a family of AlkBs in which both electron transfer partners (a ferredoxin and a ferredoxin reductase) appear as an N-terminal gene fusion to the hydroxylase (ferr_ferrR_AlkB). This enzyme catalyzes the hydroxylation of medium chain alkanes (C6-C14), with a preference for C10-C12. It requires only NADH for activity. It is present in a number of bacteria that are known to be human pathogens. A survey of the genome neighborhoods in which is it found suggest it may be involved in alkane metabolism, perhaps facilitating growth of pathogens in non-host environments.
Collapse
|
6
|
Williams SC, Austin RN. An Overview of the Electron-Transfer Proteins That Activate Alkane Monooxygenase (AlkB). Front Microbiol 2022; 13:845551. [PMID: 35295299 PMCID: PMC8918992 DOI: 10.3389/fmicb.2022.845551] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2021] [Accepted: 01/24/2022] [Indexed: 11/13/2022] Open
Abstract
Alkane-oxidizing enzymes play an important role in the global carbon cycle. Alkane monooxygenase (AlkB) oxidizes most of the medium-chain length alkanes in the environment. The first AlkB identified was from P. putida GPo1 (initially known as P. oleovorans) in the early 1970s, and it continues to be the family member about which the most is known. This AlkB is found as part of the OCT operon, in which all of the key proteins required for growth on alkanes are present. The AlkB catalytic cycle requires that the diiron active site be reduced. In P. putida GPo1, electrons originate from NADH and arrive at AlkB via the intermediacy of a flavin reductase and an iron–sulfur protein (a rubredoxin). In this Mini Review, we will review what is known about the canonical arrangement of electron-transfer proteins that activate AlkB and, more importantly, point to several other arrangements that are possible. These other arrangements include the presence of a simpler rubredoxin than what is found in the canonical arrangement, as well as two other classes of AlkBs with fused electron-transfer partners. In one class, a rubredoxin is fused to the hydroxylase and in another less well-explored class, a ferredoxin reductase and a ferredoxin are fused to the hydroxylase. We review what is known about the biochemistry of these electron-transfer proteins, speculate on the biological significance of this diversity, and point to key questions for future research.
Collapse
Affiliation(s)
| | - Rachel Narehood Austin
- Department of Chemistry, Barnard College, Columbia University, New York City, NY, United States
- *Correspondence: Rachel Narehood Austin,
| |
Collapse
|
7
|
Park C, Park W. Survival and Energy Producing Strategies of Alkane Degraders Under Extreme Conditions and Their Biotechnological Potential. Front Microbiol 2018; 9:1081. [PMID: 29910779 PMCID: PMC5992423 DOI: 10.3389/fmicb.2018.01081] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2017] [Accepted: 05/07/2018] [Indexed: 11/17/2022] Open
Abstract
Many petroleum-polluted areas are considered as extreme environments because of co-occurrence of low and high temperatures, high salt, and acidic and anaerobic conditions. Alkanes, which are major constituents of crude oils, can be degraded under extreme conditions, both aerobically and anaerobically by bacteria and archaea of different phyla. Alkane degraders possess exclusive metabolic pathways and survival strategies, which involve the use of protein and RNA chaperones, compatible solutes, biosurfactants, and exopolysaccharide production for self-protection during harsh environmental conditions such as oxidative and osmotic stress, and ionic nutrient-shortage. Recent findings suggest that the thermophilic sulfate-reducing archaeon Archaeoglobus fulgidus uses a novel alkylsuccinate synthase for long-chain alkane degradation, and the thermophilic Candidatus Syntrophoarchaeum butanivorans anaerobically oxidizes butane via alkyl-coenzyme M formation. In addition, gene expression data suggest that extremophiles produce energy via the glyoxylate shunt and the Pta-AckA pathway when grown on a diverse range of alkanes under stress conditions. Alkane degraders possess biotechnological potential for bioremediation because of their unusual characteristics. This review will provide genomic and molecular insights on alkane degraders under extreme conditions.
Collapse
Affiliation(s)
- Chulwoo Park
- Laboratory of Molecular Environmental Microbiology, Department of Environmental Science and Ecological Engineering, Korea University, Seoul, South Korea
| | - Woojun Park
- Laboratory of Molecular Environmental Microbiology, Department of Environmental Science and Ecological Engineering, Korea University, Seoul, South Korea
| |
Collapse
|
8
|
Park H, Ahn HM, Jeong HY, Kim C, Lee D. Non-Heme Iron Catalysts for Olefin Epoxidation: Conformationally Rigid Aryl-Aryl Junction To Support Amine/Imine Multidentate Ligands. Chemistry 2018; 24:8632-8638. [DOI: 10.1002/chem.201800447] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Indexed: 12/31/2022]
Affiliation(s)
- Hyunchang Park
- Department of Chemistry; Seoul National University; 1 Gwanak-ro Gwanak-gu Seoul 08826 Korea
| | - Hye Mi Ahn
- Department of Fine Chemistry; Seoul National University of Science and Technology; 232 Gongneung-ro Nowon-gu Seoul 01811 Korea
| | - Ha Young Jeong
- Department of Fine Chemistry; Seoul National University of Science and Technology; 232 Gongneung-ro Nowon-gu Seoul 01811 Korea
| | - Cheal Kim
- Department of Fine Chemistry; Seoul National University of Science and Technology; 232 Gongneung-ro Nowon-gu Seoul 01811 Korea
| | - Dongwhan Lee
- Department of Chemistry; Seoul National University; 1 Gwanak-ro Gwanak-gu Seoul 08826 Korea
| |
Collapse
|
9
|
Huang X, Groves JT. Oxygen Activation and Radical Transformations in Heme Proteins and Metalloporphyrins. Chem Rev 2018; 118:2491-2553. [PMID: 29286645 PMCID: PMC5855008 DOI: 10.1021/acs.chemrev.7b00373] [Citation(s) in RCA: 582] [Impact Index Per Article: 97.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Indexed: 12/20/2022]
Abstract
As a result of the adaptation of life to an aerobic environment, nature has evolved a panoply of metalloproteins for oxidative metabolism and protection against reactive oxygen species. Despite the diverse structures and functions of these proteins, they share common mechanistic grounds. An open-shell transition metal like iron or copper is employed to interact with O2 and its derived intermediates such as hydrogen peroxide to afford a variety of metal-oxygen intermediates. These reactive intermediates, including metal-superoxo, -(hydro)peroxo, and high-valent metal-oxo species, are the basis for the various biological functions of O2-utilizing metalloproteins. Collectively, these processes are called oxygen activation. Much of our understanding of the reactivity of these reactive intermediates has come from the study of heme-containing proteins and related metalloporphyrin compounds. These studies not only have deepened our understanding of various functions of heme proteins, such as O2 storage and transport, degradation of reactive oxygen species, redox signaling, and biological oxygenation, etc., but also have driven the development of bioinorganic chemistry and biomimetic catalysis. In this review, we survey the range of O2 activation processes mediated by heme proteins and model compounds with a focus on recent progress in the characterization and reactivity of important iron-oxygen intermediates. Representative reactions initiated by these reactive intermediates as well as some context from prior decades will also be presented. We will discuss the fundamental mechanistic features of these transformations and delineate the underlying structural and electronic factors that contribute to the spectrum of reactivities that has been observed in nature as well as those that have been invented using these paradigms. Given the recent developments in biocatalysis for non-natural chemistries and the renaissance of radical chemistry in organic synthesis, we envision that new enzymatic and synthetic transformations will emerge based on the radical processes mediated by metalloproteins and their synthetic analogs.
Collapse
Affiliation(s)
- Xiongyi Huang
- Department
of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
- Department
of Chemistry, California Institute of Technology, Pasadena, California 91125, United States
| | - John T. Groves
- Department
of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
| |
Collapse
|
10
|
Hsieh CH, Huang X, Amaya JA, Rutland CD, Keys CL, Groves JT, Austin RN, Makris TM. The Enigmatic P450 Decarboxylase OleT Is Capable of, but Evolved To Frustrate, Oxygen Rebound Chemistry. Biochemistry 2017; 56:3347-3357. [PMID: 28603981 DOI: 10.1021/acs.biochem.7b00338] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
OleT is a cytochrome P450 enzyme that catalyzes the removal of carbon dioxide from variable chain length fatty acids to form 1-alkenes. In this work, we examine the binding and metabolic profile of OleT with shorter chain length (n ≤ 12) fatty acids that can form liquid transportation fuels. Transient kinetics and product analyses confirm that OleT capably activates hydrogen peroxide with shorter substrates to form the high-valent intermediate Compound I and largely performs C-C bond scission. However, the enzyme also produces fatty alcohol side products using the high-valent iron oxo chemistry commonly associated with insertion of oxygen into hydrocarbons. When presented with a short chain fatty acid that can initiate the formation of Compound I, OleT oxidizes the diagnostic probe molecules norcarane and methylcyclopropane in a manner that is reminiscent of reactions of many CYP hydroxylases with radical clock substrates. These data are consistent with a decarboxylation mechanism in which Compound I abstracts a substrate hydrogen atom in the initial step. Positioning of the incipient substrate radical is a crucial element in controlling the efficiency of activated OH rebound.
Collapse
Affiliation(s)
- Chun H Hsieh
- Department of Chemistry and Biochemistry, University of South Carolina , Columbia, South Carolina 29208, United States
| | - Xiongyi Huang
- Department of Chemistry, Princeton University , Princeton, New Jersey 08544, United States
| | - José A Amaya
- Department of Chemistry and Biochemistry, University of South Carolina , Columbia, South Carolina 29208, United States
| | - Cooper D Rutland
- Department of Chemistry and Biochemistry, University of South Carolina , Columbia, South Carolina 29208, United States
| | - Carson L Keys
- Department of Chemistry and Biochemistry, University of South Carolina , Columbia, South Carolina 29208, United States
| | - John T Groves
- Department of Chemistry, Princeton University , Princeton, New Jersey 08544, United States
| | - Rachel N Austin
- Department of Chemistry, Barnard College, Columbia University , New York, New York 10027, United States
| | - Thomas M Makris
- Department of Chemistry and Biochemistry, University of South Carolina , Columbia, South Carolina 29208, United States
| |
Collapse
|
11
|
Yang CL, Lin CH, Luo WI, Lee TL, Ramu R, Ng KY, Tsai YF, Wei GT, Yu SSF. Mechanistic Study of the Stereoselective Hydroxylation of [2-2
H1
,3-2
H1
]Butanes Catalyzed by Cytochrome P450 BM3 Variants. Chemistry 2016; 23:2571-2582. [DOI: 10.1002/chem.201603956] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2016] [Indexed: 11/06/2022]
Affiliation(s)
- Chung-Ling Yang
- Institute of Chemistry; Academia Sinica; Taipei 115 Taiwan
- Graduate Institute of Applied Science and Technology; National (Taiwan) University of Science and Technology; Taipei 106 Taiwan
| | - Cheng-Hung Lin
- Institute of Chemistry; Academia Sinica; Taipei 115 Taiwan
- Department of Chemistry and Biochemistry; National Chung Cheng University; Chiayi 621 Taiwan
| | - Wen-I Luo
- Institute of Chemistry; Academia Sinica; Taipei 115 Taiwan
| | - Tsu-Lin Lee
- Institute of Chemistry; Academia Sinica; Taipei 115 Taiwan
- Graduate Institute of Applied Science and Technology; National (Taiwan) University of Science and Technology; Taipei 106 Taiwan
| | - Ravirala Ramu
- Institute of Chemistry; Academia Sinica; Taipei 115 Taiwan
| | - Kok Yaoh Ng
- Institute of Chemistry; Academia Sinica; Taipei 115 Taiwan
| | - Yi-Fang Tsai
- Institute of Chemistry; Academia Sinica; Taipei 115 Taiwan
| | - Guor-Tzo Wei
- Department of Chemistry and Biochemistry; National Chung Cheng University; Chiayi 621 Taiwan
| | - Steve S.-F. Yu
- Institute of Chemistry; Academia Sinica; Taipei 115 Taiwan
- Graduate Institute of Applied Science and Technology; National (Taiwan) University of Science and Technology; Taipei 106 Taiwan
| |
Collapse
|
12
|
Huang X, Groves JT. Beyond ferryl-mediated hydroxylation: 40 years of the rebound mechanism and C-H activation. J Biol Inorg Chem 2016; 22:185-207. [PMID: 27909920 PMCID: PMC5350257 DOI: 10.1007/s00775-016-1414-3] [Citation(s) in RCA: 195] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Accepted: 11/03/2016] [Indexed: 11/24/2022]
Abstract
Since our initial report in 1976, the oxygen rebound mechanism has become the consensus mechanistic feature for an expanding variety of enzymatic C-H functionalization reactions and small molecule biomimetic catalysts. For both the biotransformations and models, an initial hydrogen atom abstraction from the substrate (R-H) by high-valent iron-oxo species (Fen=O) generates a substrate radical and a reduced iron hydroxide, [Fen-1-OH ·R]. This caged radical pair then evolves on a complicated energy landscape through a number of reaction pathways, such as oxygen rebound to form R-OH, rebound to a non-oxygen atom affording R-X, electron transfer of the incipient radical to yield a carbocation, R+, desaturation to form olefins, and radical cage escape. These various flavors of the rebound process, often in competition with each other, give rise to the wide range of C-H functionalization reactions performed by iron-containing oxygenases. In this review, we first recount the history of radical rebound mechanisms, their general features, and key intermediates involved. We will discuss in detail the factors that affect the behavior of the initial caged radical pair and the lifetimes of the incipient substrate radicals. Several representative examples of enzymatic C-H transformations are selected to illustrate how the behaviors of the radical pair [Fen-1-OH ·R] determine the eventual reaction outcome. Finally, we discuss the powerful potential of "radical rebound" processes as a general paradigm for developing novel C-H functionalization reactions with synthetic, biomimetic catalysts. We envision that new chemistry will continue to arise by bridging enzymatic "radical rebound" with synthetic organic chemistry.
Collapse
|
13
|
Bertrand EM, Keddis R, Groves JT, Vetriani C, Austin RN. Identity and mechanisms of alkane-oxidizing metalloenzymes from deep-sea hydrothermal vents. Front Microbiol 2013; 4:109. [PMID: 23825470 PMCID: PMC3695450 DOI: 10.3389/fmicb.2013.00109] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2013] [Accepted: 04/16/2013] [Indexed: 12/21/2022] Open
Abstract
Six aerobic alkanotrophs (organism that can metabolize alkanes as their sole carbon source) isolated from deep-sea hydrothermal vents were characterized using the radical clock substrate norcarane to determine the metalloenzyme and reaction mechanism used to oxidize alkanes. The organisms studied were Alcanivorax sp. strains EPR7 and MAR14, Marinobacter sp. strain EPR21, Nocardioides sp. strains EPR26w, EPR28w, and Parvibaculum hydrocarbonoclasticum strain EPR92. Each organism was able to grow on n-alkanes as the sole carbon source and therefore must express genes encoding an alkane-oxidizing enzyme. Results from the oxidation of the radical-clock diagnostic substrate norcarane demonstrated that five of the six organisms (EPR7, MAR14, EPR21, EPR26w, and EPR28w) used an alkane hydroxylase functionally similar to AlkB to catalyze the oxidation of medium-chain alkanes, while the sixth organism (EPR92) used an alkane-oxidizing cytochrome P450 (CYP)-like protein to catalyze the oxidation. DNA sequencing indicated that EPR7 and EPR21 possess genes encoding AlkB proteins, while sequencing results from EPR92 confirmed the presence of a gene encoding CYP-like alkane hydroxylase, consistent with the results from the norcarane experiments.
Collapse
Affiliation(s)
- Erin M Bertrand
- Department of Chemistry, Bates College Lewiston, ME, USA ; Microbial and Environmental Genomics, J. Craig Venter Institute San Diego, CA, USA
| | | | | | | | | |
Collapse
|
14
|
Naing SH, Parvez S, Pender-Cudlip M, Groves JT, Austin RN. Substrate specificity and reaction mechanism of purified alkane hydroxylase from the hydrocarbonoclastic bacterium Alcanivorax borkumensis (AbAlkB). J Inorg Biochem 2013; 121:46-52. [PMID: 23337786 PMCID: PMC3595352 DOI: 10.1016/j.jinorgbio.2012.12.012] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2012] [Revised: 12/13/2012] [Accepted: 12/14/2012] [Indexed: 10/27/2022]
Abstract
An alkane hydroxylase from the marine organism Alcanivorax borkumensis (AbAlkB) was purified. The purified protein retained high activity in an assay with purified rubredoxin (AlkG), purified maize ferredoxin reductase, NADPH, and selected substrates. The reaction mechanism of the purified protein was probed using the radical clock substrates bicyclo[4.1.0]heptane (norcarane), bicyclo[3.1.0]hexane (bicyclohexane), methylphenylcyclopropane and deuterated and non-deuterated cyclohexane. The distribution of products from the radical clock substrates supports the hypothesis that purified AbAlkB hydroxylates substrates by forming a substrate radical. Experiments with deuterated cyclohexane indicate that the rate-determining step has a significant CH bond breaking character. The products formed from a number of differently shaped and sized substrates were characterized to determine the active site constraints of this AlkB. AbAlkB can catalyze the hydroxylation of a large number of aromatic compounds and linear and cyclic alkanes. It does not catalyze the hydroxylation of alkanes with a chain length longer than 15 carbons, nor does it hydroxylate sterically hindered C-H bonds.
Collapse
Affiliation(s)
- Swe-Htet Naing
- Department of Chemistry, Bates College, 5 Andrews Rd. Lewiston ME 04240, 207-786-6295, fax: 207-786-8336
| | - Saba Parvez
- Department of Chemistry, Bates College, 5 Andrews Rd. Lewiston ME 04240, 207-786-6295, fax: 207-786-8336
| | - Marilla Pender-Cudlip
- Department of Chemistry, Bates College, 5 Andrews Rd. Lewiston ME 04240, 207-786-6295, fax: 207-786-8336
| | - John T. Groves
- Department of Chemistry, Princeton University, Princeton NJ 08544
| | - Rachel N. Austin
- Department of Chemistry, Bates College, 5 Andrews Rd. Lewiston ME 04240, 207-786-6295, fax: 207-786-8336
| |
Collapse
|
15
|
Cooper HLR, Mishra G, Huang X, Pender-Cudlip M, Austin RN, Shanklin J, Groves JT. Parallel and competitive pathways for substrate desaturation, hydroxylation, and radical rearrangement by the non-heme diiron hydroxylase AlkB. J Am Chem Soc 2012; 134:20365-75. [PMID: 23157204 PMCID: PMC3531984 DOI: 10.1021/ja3059149] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A purified and highly active form of the non-heme diiron hydroxylase AlkB was investigated using the diagnostic probe substrate norcarane. The reaction afforded C2 (26%) and C3 (43%) hydroxylation and desaturation products (31%). Initial C-H cleavage at C2 led to 7% C2 hydroxylation and 19% 3-hydroxymethylcyclohexene, a rearrangement product characteristic of a radical rearrangement pathway. A deuterated substrate analogue, 3,3,4,4-norcarane-d(4), afforded drastically reduced amounts of C3 alcohol (8%) and desaturation products (5%), while the radical rearranged alcohol was now the major product (65%). This change in product ratios indicates a large kinetic hydrogen isotope effect of ∼20 for both the C-H hydroxylation at C3 and the desaturation pathway, with all of the desaturation originating via hydrogen abstraction at C3 and not C2. The data indicate that AlkB reacts with norcarane via initial C-H hydrogen abstraction from C2 or C3 and that the three pathways, C3 hydroxylation, C3 desaturation, and C2 hydroxylation/radical rearrangement, are parallel and competitive. Thus, the incipient radical at C3 either reacts with the iron-oxo center to form an alcohol or proceeds along the desaturation pathway via a second H-abstraction to afford both 2-norcarene and 3-norcarene. Subsequent reactions of these norcarenes lead to detectable amounts of hydroxylation products and toluene. By contrast, the 2-norcaranyl radical intermediate leads to C2 hydroxylation and the diagnostic radical rearrangement, but this radical apparently does not afford desaturation products. The results indicate that C-H hydroxylation and desaturation follow analogous stepwise reaction channels via carbon radicals that diverge at the product-forming step.
Collapse
Affiliation(s)
| | - Girish Mishra
- Department of Biology, Brookhaven National Laboratory, 50 Bell Avenue, Upton, NY 11973
| | - Xiongyi Huang
- Department of Chemistry, Princeton University, Princeton NJ 08544
| | | | | | - John Shanklin
- Department of Biology, Brookhaven National Laboratory, 50 Bell Avenue, Upton, NY 11973
| | - John T. Groves
- Department of Chemistry, Princeton University, Princeton NJ 08544
| |
Collapse
|
16
|
Genome sequence of n-alkane-degrading Hydrocarboniphaga effusa strain AP103T (ATCC BAA-332T). J Bacteriol 2012; 194:5120. [PMID: 22933753 DOI: 10.1128/jb.01017-12] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Hydrocarboniphaga effusa strain AP103(T) (ATCC BAA-332(T)) is a member of the Gammaproteobacteria utilizing n-alkanes as the sole source of carbon and energy. Here we report the draft genome sequence of AP103(T), which consists of 5,193,926 bp with a G + C content of 65.18%.
Collapse
|
17
|
Peter S, Kinne M, Wang X, Ullrich R, Kayser G, Groves JT, Hofrichter M. Selective hydroxylation of alkanes by an extracellular fungal peroxygenase. FEBS J 2011; 278:3667-75. [PMID: 21812933 DOI: 10.1111/j.1742-4658.2011.08285.x] [Citation(s) in RCA: 99] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Fungal peroxygenases are novel extracellular heme-thiolate biocatalysts that are capable of catalyzing the selective monooxygenation of diverse organic compounds, using only H(2)O(2) as a cosubstrate. Little is known about the physiological role or the catalytic mechanism of these enzymes. We have found that the peroxygenase secreted by Agrocybe aegerita catalyzes the H(2)O(2)-dependent hydroxylation of linear alkanes at the 2-position and 3-position with high efficiency, as well as the regioselective monooxygenation of branched and cyclic alkanes. Experiments with n-heptane and n-octane showed that the hydroxylation proceeded with complete stereoselectivity for the (R)-enantiomer of the corresponding 3-alcohol. Investigations with a number of model substrates provided information about the route of alkane hydroxylation: (a) the hydroxylation of cyclohexane mediated by H(2)(18)(2) resulted in complete incorporation of (18)O into the hydroxyl group of the product cyclohexanol; (b) the hydroxylation of n-hexane-1,1,1,2,2,3,3-D(7) showed a large intramolecular deuterium isotope effect [(k(H)/k(D))(obs)] of 16.0 ± 1.0 for 2-hexanol and 8.9 ± 0.9 for 3-hexanol; and (c) the hydroxylation of the radical clock norcarane led to an estimated radical lifetime of 9.4 ps and an oxygen rebound rate of 1.06 × 10(11) s(-1). These results point to a hydrogen abstraction and oxygen rebound mechanism for alkane hydroxylation. The peroxygenase appeared to lack activity on long-chain alkanes (> C(16)) and highly branched alkanes (e.g. tetramethylpentane), but otherwise exhibited a broad substrate range. It may accordingly have a role in the bioconversion of natural and anthropogenic alkane-containing structures (including alkyl chains of complex biomaterials) in soils, plant litter, and wood.
Collapse
Affiliation(s)
- Sebastian Peter
- Department of Bio- and Environmental Sciences, International Graduate School of Zittau, Zittau, Germany
| | | | | | | | | | | | | |
Collapse
|
18
|
|
19
|
Production of a recombinant alkane hydroxylase (AlkB2) from Alcanivorax borkumensis. Biotechnol Lett 2009; 32:497-502. [PMID: 19953301 DOI: 10.1007/s10529-009-0177-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2009] [Revised: 11/10/2009] [Accepted: 11/10/2009] [Indexed: 10/20/2022]
Abstract
Alcanivorax borkumensis is an oil-degrading marine bacterium. Its genome contains genes coding for three cytochrome P450s and two integral membrane alkane hydroxylases (AlkB1 & AlkB2), all assumed to perform hydroxylation of different linear or branched alkanes. Although, the sequence of alkB2 has been determined, the molecular characterization and the substrate specificity of AlkB2 require more precise investigation. In this study, AlkB2 from A. borkumensis SK2 was expressed in Escherichia coli to examine the functionality of AlkB2 as a hydroxylating enzyme. Furthermore, the activity of the enzyme in the presence of the accessory proteins, rubredoxin (RubA) and rubredoxin reductase (RubB), produced in E. coli BL21(DE3)plysS cells, was determined. Recombinant AlkB2 is produced in an active form and rubredoxin is the intermediate electron donor to AlkB2 and can replace AlkG function, when NADH is the prime electron donor.
Collapse
|
20
|
Austin RN, Luddy K, Erickson K, Pender-Cudlip M, Bertrand E, Deng D, Buzdygon RS, van Beilen JB, Groves JT. Cage escape competes with geminate recombination during alkane hydroxylation by the diiron oxygenase AlkB. Angew Chem Int Ed Engl 2008; 47:5232-4. [PMID: 18512839 DOI: 10.1002/anie.200801184] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Rachel N Austin
- Department of Chemistry, Bates College, Lewiston ME 04240, USA.
| | | | | | | | | | | | | | | | | |
Collapse
|
21
|
Austin R, Luddy K, Erickson K, Pender‐Cudlip M, Bertrand E, Deng D, Buzdygon R, van Beilen J, Groves J. Cage Escape Competes with Geminate Recombination during Alkane Hydroxylation by the Diiron Oxygenase AlkB. Angew Chem Int Ed Engl 2008. [DOI: 10.1002/ange.200801184] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
|