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Insights into the Reaction Mechanism of Soluble Epoxide Hydrolase from Theoretical Active Site Mutants
KTH, School of Biotechnology (BIO), Theoretical Chemistry.
KTH, School of Biotechnology (BIO), Theoretical Chemistry.
2006 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, no 42, 21299-21310 p.Article in journal (Refereed) Published
Abstract [en]

Density functional theory calculations of active site mutants are used to gain insights into the reaction mechanism of the soluble epoxide hydrolases (sEHs). The quantum chemical model is based on the X-ray crystal structure of the human soluble epoxide hydrolase. The role of two conserved active site tyrosines is explored through in silico single and double mutations to phenylalanine. Full potential energy curves for hydrolysis of (1S,2S)-beta-methylstyrene oxide are presented. The results indicate that the two active site tyrosines act in concert to lower the activation barrier for the alkylation step. For the wild-type and three different tyrosine mutant models, the regioselectivity of epoxide opening is compared for the substrates (1S,2S)-beta-methylstyrene oxide and (S)-styrene oxide. An additional part of our study focuses on the importance of the catalytic histidine for the alkylation half-reaction. Different models are presented to explore the protonation state of the catalytic histidine in the alkylation step and to evaluate the possibility of an interaction between the nucleophilic aspartate and the catalytic histidine.

Place, publisher, year, edition, pages
2006. Vol. 110, no 42, 21299-21310 p.
Keyword [en]
Enzyme kinetics; Hydrolysis; Mutagenesis; Potential energy; Probability density function; Quantum theory; Activation barriers; Active site tyrosines; Potential energy curves; Silico singles
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-8105DOI: 10.1021/jp063830tISI: 000241381600086Scopus ID: 2-s2.0-33751280486OAI: oai:DiVA.org:kth-8105DiVA: diva2:13336
Note
QC 20100811Available from: 2008-03-18 Created: 2008-03-18 Last updated: 2010-08-11Bibliographically approved
In thesis
1. Nitrile Hydratases and Epoxide-Transforming Enzymes: Quantum Chemical Modeling of Reaction Mechanisms and Selectivities
Open this publication in new window or tab >>Nitrile Hydratases and Epoxide-Transforming Enzymes: Quantum Chemical Modeling of Reaction Mechanisms and Selectivities
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Quantum chemical studies of enzymatic reactions are able to provide detailed insight into mechanisms and catalytic strategies. The energetic feasibility of proposed mechanisms can be established, and new possible reaction pathways can be put forward. The role of the involved active site residues can be analyzed in detail and the origins for experimentally observed selectivities can be investigated. Density functional theory (DFT), in particular the hybrid functional B3LYP, is the method of choice in this kind of studies.

In this thesis, the reaction mechanisms of several enzymes have been explored using the B3LYP functional. The studied enzymes include limonene epoxide hydrolase (LEH), soluble epoxide hydrolase (sEH), haloalcohol dehalogenase (HheC), and nitrile hydratase (NHase). Transition states and intermediates along various reaction pathways were optimized and evaluated.

For the three epoxide-transforming enzymes, the role of the proposed catalytic residues could be confirmed. Analysis of in silico mutations helped to quantify the effect of various functional groups on the barriers and regioselectivities of epoxide opening. A detailed analysis of the factors governing the enzymatic regioselectivities is given.

For nitrile hydratase, various putative first- and second-shell mechanisms have been studied. Active site models based on both the Co(III)-NHase and the Fe(III)-NHase were employed. The studied mechanisms include general base-catalyzed reaction pathways with water as nucleophile as well as two pathways involving cysteine-sulfenate as nucleophile. Several computed mechanisms exhibit similar barriers, making it difficult to pinpoint the true NHase mechanism.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. x, 74 p.
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2008:1
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:kth:diva-4668 (URN)978-91-7178-885-6 (ISBN)
Public defence
2008-04-04, FB52, AlbaNova, Roslagstullsbacken 21, Stockholm, 10:30
Opponent
Supervisors
Note
QC 20100811Available from: 2008-03-18 Created: 2008-03-18 Last updated: 2010-08-11Bibliographically approved
2. Quantum chemical studies of epoxide-transforming enzymes
Open this publication in new window or tab >>Quantum chemical studies of epoxide-transforming enzymes
2007 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

Density functional theory is employed to study the reaction mechanisms of different epoxide-transforming enzymes. Calculations are based on quantum chemical active site models, which are build from X-ray crystal structures. The models are used to study conversion of various epoxides into their corresponding diols or substituted alcohols. Epoxide-transforming enzymes from three different families are studied. The human soluble epoxide hydrolase (sEH) belongs to the α/β-hydrolase fold family. sEH employs a covalent mechanism to hydrolyze various epoxides into vicinal diols. The Rhodococcus erythrobacter limonene epoxide hydrolase (LEH) constitutes a novel epoxide hydrolase, which is considered the founding member of a new family of enzymes. LEH mediates transformation of limone-1,2-epoxide into the corresponding vicinal diol by employing a general acid/general base-mediated mechanism. The Agrobacterium radiobacter AD1 haloalcohol dehalogenase HheC is related to the short-chain dehydrogenase/reductases. HheC is able to convert epoxides using various nucleophiles such as azide, cyanide, and nitrite. Reaction mechanisms of these three enzymes are analyzed in depth and the role of different active site residues is studied through in silico mutations. Steric and electronic factors influencing the regioselectivity of epoxide opening are identified. The computed energetics help to explain preferred reaction pathways and experimentally observed regioselectivities. Our results confirm the usefulness of the employed computational methodology for investigating enzymatic reactions.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. x, 58 p.
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2007:3
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:kth:diva-4390 (URN)978-91-7178-640-1 (ISBN)
Presentation
2007-05-11, FD41, AlbaNova, 10:00
Opponent
Supervisors
Note
QC 20101108Available from: 2007-05-22 Created: 2007-05-22 Last updated: 2010-11-08Bibliographically approved

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