scholarly journals One-megadalton metalloenzyme complex inGeobacter metallireducensinvolved in benzene ring reduction beyond the biological redox window

2019 ◽  
Vol 116 (6) ◽  
pp. 2259-2264 ◽  
Author(s):  
Simona G. Huwiler ◽  
Claudia Löffler ◽  
Sebastian E. L. Anselmann ◽  
Hans-Joachim Stärk ◽  
Martin von Bergen ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Benzene Ring ◽  
Active Site ◽  
Anaerobic Bacterium ◽  
Class Ii ◽  
High Molecular Mass ◽  
Redox Potentials ◽  
Geobacter Metallireducens ◽  
Redox Couples ◽  
Biological Electron Transfer

Reversible biological electron transfer usually occurs between redox couples at standard redox potentials ranging from +0.8 to −0.5 V. Dearomatizing benzoyl-CoA reductases (BCRs), key enzymes of the globally relevant microbial degradation of aromatic compounds at anoxic sites, catalyze a biological Birch reduction beyond the negative limit of this redox window. The structurally characterized BamBC subunits of class II BCRs accomplish benzene ring reduction at an active-site tungsten cofactor; however, the mechanism and components involved in the energetic coupling of endergonic benzene ring reduction have remained hypothetical. We present a 1-MDa, membrane-associated, Bam[(BC)2DEFGHI]2complex from the anaerobic bacteriumGeobacter metallireducensharboring 4 tungsten, 4 zinc, 2 selenocysteines, 6 FAD, and >50 FeS cofactors. The results suggest that class II BCRs catalyze electron transfer to the aromatic ring, yielding a cyclic 1,5-dienoyl-CoA via two flavin-based electron bifurcation events. This work expands our knowledge of energetic couplings in biology by high-molecular-mass electron bifurcating machineries.

scholarly journals Refining the reaction mechanism of O2 towards its substrate in cofactor-free dioxygenases

2016 ◽  
Author(s):  
Pedro J Silva
Keyword(s):  
Electron Transfer ◽  
Active Site ◽  
Quantum Chemical ◽  
Potential Energy Surfaces ◽  
Direct Electron Transfer ◽  
Minimum Energy ◽  
Urate Oxidase ◽  
Redox Potentials ◽  
Deprotonated Form ◽  
Quantum Chemical Computations

Cofactor-less oxygenases perform challenging catalytic reactions between singlet substrates and triplet oxygen, in spite of apparently violating the spin-conservation rule. In bacterial ring-cleaving 2,4-dioxygenase, the active site has been suggested by quantum chemical computations to fine tune triplet oxygen reactivity, allowing it to interact rapidly with its singlet substrate without the need for spin inversion, and in urate oxidase the reaction is thought to proceed through electron transfer from the deprotonated substrate to an aminoacid sidechain, which then feeds the electron to the oxygen molecule. In this work, we perform additional quantum chemical computations on these two systems to elucidate several intriguing features unaddressed by previous workers. These computations establish that in both enzymes the reaction proceeds through direct electron transfer from substrate to O2 followed by radical recombination, instead of minimum-energy crossing points between singlet and triplet potential energy surfaces without formal electron transfer. The active site does not affect the reactivity of oxygen directly but is crucial for the generation of the deprotonated form of the substrates, which have redox potentials far below those of their protonated forms and therefore may transfer electrons to oxygen without sizeable thermodynamic barriers. This mechanism seems to be shared by most cofactor-less oxidases studied so far.

scholarly journals Electron transfer within β-diketiminato nickel bromide and cobaltocene redox couples activating CO2

2021 ◽  
Author(s):  
Philipp Zimmermann ◽  
Alexander F. R. Kilpatrick ◽  
Deniz Ar ◽  
Serhiy Demeshko ◽  
Beatrice Cula ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Redox Potentials ◽  
Redox Couples ◽  
Electron Transfer Complex

Even though β-diketiminato nickel(ii) bromide and cobaltocene have nearly identical redox potentials the corresponding electron transfer complex can be crystallised from the equilibrium and activates CO2 to form a mononuclear nickel(ii) carbonate.

scholarly journals Refining the reaction mechanism of O2 towards its substrate in cofactor-free dioxygenases

2016 ◽  
Author(s):  
Pedro J Silva
Keyword(s):  
Electron Transfer ◽  
Active Site ◽  
Quantum Chemical ◽  
Potential Energy Surfaces ◽  
Direct Electron Transfer ◽  
Minimum Energy ◽  
Urate Oxidase ◽  
Redox Potentials ◽  
Deprotonated Form ◽  
Quantum Chemical Computations

Cofactor-less oxygenases perform challenging catalytic reactions between singlet substrates and triplet oxygen, in spite of apparently violating the spin-conservation rule. In bacterial ring-cleaving 2,4-dioxygenase, the active site has been suggested by quantum chemical computations to fine tune triplet oxygen reactivity, allowing it to interact rapidly with its singlet substrate without the need for spin inversion, and in urate oxidase the reaction is thought to proceed through electron transfer from the deprotonated substrate to an aminoacid sidechain, which then feeds the electron to the oxygen molecule. In this work, we perform additional quantum chemical computations on these two systems to elucidate several intriguing features unaddressed by previous workers. These computations establish that in both enzymes the reaction proceeds through direct electron transfer from substrate to O2 followed by radical recombination, instead of minimum-energy crossing points between singlet and triplet potential energy surfaces without formal electron transfer. The active site does not affect the reactivity of oxygen directly but is crucial for the generation of the deprotonated form of the substrates, which have redox potentials far below those of their protonated forms and therefore may transfer electrons to oxygen without sizeable thermodynamic barriers. This mechanism seems to be shared by most cofactor-less oxidases studied so far.

scholarly journals Electrochemical Studies of a Truncated Laccase Produced in Pichia pastoris

1999 ◽  
Vol 65 (12) ◽  
pp. 5515-5521 ◽  
Author(s):  
Mirjana Gelo-Pujic ◽  
Hyug-Han Kim ◽  
Nathan G. Butlin ◽  
G. Tayhas R. Palmore
Keyword(s):  
Electron Transfer ◽  
Pichia Pastoris ◽  
Active Site ◽  
Relative Activity ◽  
Cysteine Residue ◽  
Site Directed Mutagenesis ◽  
Electrochemical Studies ◽  
Redox Potentials ◽  
Hydrogen Electrode ◽  
C Terminus

ABSTRACT The cDNA that encodes an isoform of laccase from Trametes versicolor (LCCI), as well as a truncated version (LCCIa), was subcloned and expressed by using the yeast Pichia pastorisas the heterologous host. The amino acid sequence of LCCIa is identical to that of LCCI except that the final 11 amino acids at the C terminus of LCCI are replaced with a single cysteine residue. This modification was introduced for the purpose of improving the kinetics of electron transfer between an electrode and the copper-containing active site of laccase. The two laccases (LCCI and LCCIa) are compared in terms of their relative activity with two substrates that have different redox potentials. Results from electrochemical studies on solutions containing LCCI and LCCIa indicate that the redox potential of the active site of LCCIa is shifted to more negative values (411 mV versus normal hydrogen electrode voltage) than that found in other fungal laccases. In addition, replacing the 11 codons at the C terminus of the laccase gene with a single cysteine codon (i.e., LCCI→LCCIa) influences the rate of heterogeneous electron transfer between an electrode and the copper-containing active site (k het for LCCIa = 1.3 × 10−4 cm s−1). These results demonstrate for the first time that the rate of electron transfer between an oxidoreductase and an electrode can be enhanced by changes to the primary structure of a protein via site-directed mutagenesis.

scholarly journals Refining the reaction mechanism of O2towards its co-substrate in cofactor-free dioxygenases

PeerJ ◽  
2016 ◽  
Vol 4 ◽  
pp. e2805 ◽  
Author(s):  
Pedro J. Silva
Keyword(s):  
Electron Transfer ◽  
Active Site ◽  
Quantum Chemical ◽  
Potential Energy Surfaces ◽  
Direct Electron Transfer ◽  
Minimum Energy ◽  
Urate Oxidase ◽  
Redox Potentials ◽  
Deprotonated Form ◽  
Quantum Chemical Computations

Cofactor-less oxygenases perform challenging catalytic reactions between singlet co-substrates and triplet oxygen, in spite of apparently violating the spin-conservation rule. In 1-H-3-hydroxy-4-oxoquinaldine-2,4-dioxygenase, the active site has been suggested by quantum chemical computations to fine tune triplet oxygen reactivity, allowing it to interact rapidly with its singlet substrate without the need for spin inversion, and in urate oxidase the reaction is thought to proceed through electron transfer from the deprotonated substrate to an aminoacid sidechain, which then feeds the electron to the oxygen molecule. In this work, we perform additional quantum chemical computations on these two systems to elucidate several intriguing features unaddressed by previous workers. These computations establish that in both enzymes the reaction proceeds through direct electron transfer from co-substrate to O2followed by radical recombination, instead of minimum-energy crossing points between singlet and triplet potential energy surfaces without formal electron transfer. The active site does not affect the reactivity of oxygen directly but is crucial for the generation of the deprotonated form of the co-substrates, which have redox potentials far below those of their protonated forms and therefore may transfer electrons to oxygen without sizeable thermodynamic barriers. This mechanism seems to be shared by most cofactor-less oxidases studied so far.

scholarly journals Insight to Microbial Fe(III) Reduction Mediated by Redox-Active Humic Acids with Varied Redox Potentials

2021 ◽  
Vol 18 (13) ◽  
pp. 6807
Author(s):  
Jingtao Duan ◽  
Zhiyuan Xu ◽  
Zhen Yang ◽  
Jie Jiang
Keyword(s):  
Molecular Weight ◽  
Electron Transfer ◽  
Humic Acids ◽  
Weight Fraction ◽  
Electrochemical Analysis ◽  
Microbial Reduction ◽  
Redox Potentials ◽  
Groundwater Environment ◽  
Redox Active ◽  
Different Molecular Weight

Redox-active humic acids (HA) are ubiquitous in terrestrial and aquatic systems and are involved in numerous electron transfer reactions affecting biogeochemical processes and fates of pollutants in soil environments. Redox-active contaminants are trapped in soil micropores (<2 nm) that have limited access to microbes and HA. Therefore, the contaminants whose molecular structure and properties are not damaged accumulate in the soil micropores and become potential pollution sources. Electron transfer capacities (ETC) of HA reflecting redox activities of low molecular weight fraction (LMWF, <2.5) HA can be detected by an electrochemical method, which is related to redox potentials (Eh) in soil and aquatic environments. Nevertheless, electron accepting capacities (EAC) and electron donating capacities (EDC) of these LMWF HA at different Eh are still unknown. EDC and EAC of different molecular weight HA at different Eh were analyzed using electrochemical methods. EAC of LMWF at −0.59 V was 12 times higher than that at −0.49 V, while EAC increased to 2.6 times when the Eh decreased from −0.59 V to −0.69 V. Afterward, LMWF can act as a shuttle to stimulate microbial Fe(III) reduction processes in microbial reduction experiments. Additionally, EAC by electrochemical analysis at a range of −0.49–−0.59 V was comparable to total calculated ETC of different molecular weight fractions of HA by microbial reduction. Therefore, it is indicated that redox-active functional groups that can be reduced at Eh range of −0.49–−0.59 are available to microbial reduction. This finding contributes to a novel perspective in the protection and remediation of the groundwater environment in the biogeochemistry process.

scholarly journals Direct Interspecies Electron Transfer between Geobacter metallireducens and Methanosarcina barkeri

2014 ◽  
Vol 80 (15) ◽  
pp. 4599-4605 ◽  
Author(s):  
Amelia-Elena Rotaru ◽  
Pravin Malla Shrestha ◽  
Fanghua Liu ◽  
Beatrice Markovaite ◽  
Shanshan Chen ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Model Organism ◽  
Methanosarcina Barkeri ◽  
Physical Contact ◽  
Acetate Metabolism ◽  
Geobacter Metallireducens ◽  
Content Type ◽  
Direct Interspecies Electron Transfer ◽  
Interspecies Electron Transfer ◽  
Effective Form

ABSTRACTDirect interspecies electron transfer (DIET) is potentially an effective form of syntrophy in methanogenic communities, but little is known about the diversity of methanogens capable of DIET. The ability ofMethanosarcina barkerito participate in DIET was evaluated in coculture withGeobacter metallireducens. Cocultures formed aggregates that shared electrons via DIET during the stoichiometric conversion of ethanol to methane. Cocultures could not be initiated with a pilin-deficientG. metallireducensstrain, suggesting that long-range electron transfer along pili was important for DIET. Amendments of granular activated carbon permitted the pilin-deficientG. metallireducensisolates to share electrons withM. barkeri, demonstrating that this conductive material could substitute for pili in promoting DIET. WhenM. barkeriwas grown in coculture with the H2-producingPelobacter carbinolicus, incapable of DIET,M. barkeriutilized H2as an electron donor but metabolized little of the acetate thatP. carbinolicusproduced. This suggested that H2, but not electrons derived from DIET, inhibited acetate metabolism.P. carbinolicus-M. barkericocultures did not aggregate, demonstrating that, unlike DIET, close physical contact was not necessary for interspecies H2transfer.M. barkeriis the second methanogen found to accept electrons via DIET and the first methanogen known to be capable of using either H2or electrons derived from DIET for CO2reduction. Furthermore,M. barkeriis genetically tractable, making it a model organism for elucidating mechanisms by which methanogens make biological electrical connections with other cells.

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