Dataset Information

Overcoming the Gas-Liquid Mass Transfer of Oxygen by Coupling Photosynthetic Water Oxidation with Biocatalytic Oxyfunctionalization.

ABSTRACT: Gas-liquid mass transfer of gaseous reactants is a major limitation for high space-time yields, especially for O₂ -dependent (bio)catalytic reactions in aqueous solutions. Herein, oxygenic photosynthesis was used for homogeneous O₂ supply via in?situ generation in the liquid phase to overcome this limitation. The phototrophic cyanobacterium Synechocystis sp. PCC6803 was engineered to synthesize the alkane monooxygenase AlkBGT from Pseudomonas putida GPo1. With light, but without external addition of O₂ , the chemo- and regioselective hydroxylation of nonanoic acid methyl ester to ?-hydroxynonanoic acid methyl ester was driven by O₂ generated through photosynthetic water oxidation. Photosynthesis also delivered the necessary reduction equivalents to regenerate the Fe²⁺ center in AlkB for oxygen transfer to the terminal methyl group. The in?situ coupling of oxygenic photosynthesis to O₂ -transferring enzymes now enables the design of fast hydrocarbon oxyfunctionalization reactions.

SUBMITTER: Hoschek A

PROVIDER: S-EPMC5708270 | biostudies-literature | 2017 Nov

REPOSITORIES: biostudies-literature

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Overcoming the Gas-Liquid Mass Transfer of Oxygen by Coupling Photosynthetic Water Oxidation with Biocatalytic Oxyfunctionalization.

Hoschek Anna A Bühler Bruno B Schmid Andreas A

Angewandte Chemie (International ed. in English) 20171027 47

Gas-liquid mass transfer of gaseous reactants is a major limitation for high space-time yields, especially for O<sub>2</sub> -dependent (bio)catalytic reactions in aqueous solutions. Herein, oxygenic photosynthesis was used for homogeneous O<sub>2</sub> supply via in situ generation in the liquid phase to overcome this limitation. The phototrophic cyanobacterium Synechocystis sp. PCC6803 was engineered to synthesize the alkane monooxygenase AlkBGT from Pseudomonas putida GPo1. With light, but wi ...[more]

PMID: 28945948

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Project description:A fundamental goal in catalysis is the coupling of multiple reactions to yield a desired product. Enzymes have evolved elegant approaches to address this grand challenge. A salient example is the biological conversion of methane to methanol catalyzed by soluble methane monooxygenase (sMMO), a member of the bacterial multicomponent monooxygenase (BMM) superfamily. sMMO is a dynamic protein complex of three components: a hydroxylase, a reductase, and a regulatory protein. The active site, a carboxylate-rich non-heme diiron center, is buried inside the 251 kDa hydroxylase component. The enzyme processes four substrates: O2, protons, electrons, and methane. To couple O2 activation to methane oxidation, timely control of substrate access to the active site is critical. Recent studies of sMMO, as well as its homologues in the BMM superfamily, have begun to unravel the mechanism. The emerging and unifying picture reveals that each substrate gains access to the active site along a specific pathway through the hydroxylase. Electrons and protons are delivered via a three-amino-acid pore located adjacent to the diiron center; O2 migrates via a series of hydrophobic cavities; and hydrocarbon substrates reach the active site through a channel or linked set of cavities. The gating of these pathways mediates entry of each substrate to the diiron active site in a timed sequence and is coordinated by dynamic interactions with the other component proteins. The result is coupling of dioxygen consumption with hydrocarbon oxidation, avoiding unproductive oxidation of the reductant rather than the desired hydrocarbon. To initiate catalysis, the reductase delivers two electrons to the diiron(III) center by binding over the pore of the hydroxylase. The regulatory component then displaces the reductase, docking onto the same surface of the hydroxylase. Formation of the hydroxylase-regulatory component complex (i) induces conformational changes of pore residues that may bring protons to the active site; (ii) connects hydrophobic cavities in the hydroxylase leading from the exterior to the diiron active site, providing a pathway for O2 and methane, in the case of sMMO, to the reduced diiron center for O2 activation and substrate hydroxylation; (iii) closes the pore, as well as a channel in the case of four-component BMM enzymes, restricting proton access to the diiron center during formation of "Fe2O2" intermediates required for hydrocarbon oxidation; and (iv) inhibits undesired electron transfer to the Fe2O2 intermediates by blocking reductase binding during O2 activation. This mechanism is quite different from that adopted by cytochromes P450, a large class of heme-containing monooxygenases that catalyze reactions very similar to those catalyzed by the BMM enzymes. Understanding the timed enzyme control of substrate access has implications for designing artificial catalysts. To achieve multiple turnovers and tight coupling, synthetic models must also control substrate access, a major challenge considering that nature requires large, multimeric, dynamic protein complexes to accomplish this feat.

Dataset Information

Overcoming the Gas-Liquid Mass Transfer of Oxygen by Coupling Photosynthetic Water Oxidation with Biocatalytic Oxyfunctionalization.

Publications

Overcoming the Gas-Liquid Mass Transfer of Oxygen by Coupling Photosynthetic Water Oxidation with Biocatalytic Oxyfunctionalization.

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