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Application and Protein Engineering of Oxidoreductases

  • The focus of the first two articles was the engineering and application of enzymes for the conversion of the bio-based resources glycerol and its oxidation product glyceraldehyde for the production of the value added product glyceric acid. Article III focuses on the cloning, exploration and engineering of a polyol dehydrogenase, which later on was used as cofactor recycling system in order to produce ε-caprolactone from cyclohexanol as presented in arti-cle IV. The following paragraphs will give a short outline of each article. ARTICLE I: ASYMMETRIC SYNTHESIS OF D-GLYCERIC ACID BY AN ALDITOL OXIDASE AND DIRECTED EVOLUTION FOR ENHANCED OXIDATIVE ACTIVITY TOWARDS GLYCEROL. GERSTENBRUCH, S., WULF, H., MUßMANN, N., O’CONNELL, T., MAURER, K.-H. & BORNSCHEUER, U. T. (2012). Appl. Microbiol. Biotechnol. 96, 1243-1252. The alditol oxidase of Streptomyces coelicolor A3(2) (AldO) was used to catalyze the oxida-tion of glycerol to glyceraldehyde and glyceric acid. The enantioselectivity for the FAD-de-pendent glycerol oxidation was elucidated and different strategies were used to enhance the substrate specificity towards glycerol. Directed evolution by error-prone PCR led to an AldO double mutant with 1.5-fold improved activity for glycerol. Further improvement of activity was achieved by combination of mutations, leading to a quadruple mutant with 2.4-fold higher specific activity towards glycerol compared to the wild-type enzyme. In small-scale biotransformation concentrations up to 2.0 g•l-1 D-glyceric acid could be reached using whole cells. Investi¬gation of the effects of the introduced mutations led to a further identification of es¬sential amino acids with respect to enzyme functionality and structural stability. ARTICLE II: KINETIC RESOLUTION OF GLYCERALDEHYDE USING AN ALDEHYDE DEHYDROGENASE FROM DEINOCOCCUS GEOTHERMALIS DSM 11300 COMBINED WITH ELECTROCHEMICAL COFACTOR RECYCLING. WULF, H., PERZBORN, M., SIEVERS, G., SCHOLZ, F. & BORNSCHEUER, U. T. (2012). J. Mol. Catal. B Enzym. 74, 144-150. Two aldehyde dehydrogenases (ALDH) from Escherichia coli BL21 and Deinococcus geother-malis were cloned, characterized and evaluated according to their applicability for a bio-catalysis setup with electrolytic cofactor recycling. Both ALDHs turned out to have a sim¬ilar substrate scope and favor short to medium chain aldehydes and both oxidize glyceralde¬hyde to D-glyceric acid. The ALDH variant of D. geothermalis shows higher specific activity towards glyceraldehyde and has an elevated optimum temperature compared to the BL21 enzyme. Due to the higher specific activity of the ALDH of D. geothermalis, this enzyme was used to conduct a kinetic resolution of glyceraldehyde with electrolytic NAD+ recycling at a glassy carbon foam electrode with ABTS as redox mediator yielding in 1.8 g•l-1 glyceric acid. ARTICLE III: PROTEIN ENGINEERING OF A THERMOSTABLE POLYOL DEHYDROGENASE. WULF, H.*, MALLIN, H.*, BORNSCHEUER U.T. (2012). Enzyme Microb. Technol. 51, 217-224 (*equally contributed). The new enzyme polyol dehydrogenase PDH-11300 from D. geothermalis was extensively characterized regarding its temperature optimum and thermostability. A peptide stretch responsible for substrate recognition from the PDH-11300 was substituted by this particular stretch of a homolog enzyme, the galactitol dehydrogenase from Rhodobacter sphaeroides (PDH-158), resulting in a chimeric enzyme (PDH-loop). The substrate scopes were deter-mined and basically the chimeric enzyme represented the average of both wild-type en-zymes. A rather unexpected finding was the notably increased T5060, by 7°C to 55.3°C, and an increased specific activity against cyclohexanol. Finally, the cofactor specificity was suc¬cess-fully altered from NADH to NADPH by an Asp55Asn mutation, which is located at the NAD+ binding cleft, without influencing the catalytic properties of the dehydrogenase. ARTICLE IV: A SELF-SUFFICIENT BAEYER-VILLIGER BIOCATALYSIS SYSTEM FOR THE SYNTHESIS OF Ɛ-CAPROLACTONE FROM CYCLOHEXANOL. MALLIN, H. *, WULF, H. *, BORNSCHEUER U.T. (2013). Enzyme Microb. Technol., online, DOI: 10.1016/j.enzmictec.2013.01.007 (*equally contributed). The application of the engineered PDH-loopN mutant [1] (Article III) for the production of ε-caprolactone from cyclohexanol was investigated in a co-immobilization approach with the cyclohexanone monooxygenase from Acinetobacter calcoaceticus. Biotransformation with solubilized enzymes led to an isolated yield of 55% pure ε-caprolactone with no residual cy-clohexanol to be detected. During the immobilization experiments a higher enzyme ratio in favor of the CHMO led to higher reaction velocities. Similarly, the addition of soluble fresh CHMO during reuse of co-immobilization batches significantly increased the activity identi-fying the CHMO as the bottleneck in this reaction setup.
  • Im Fokus der ersten beiden Artikel standen die biokatalytische Herstellung von Glycerinderivaten sowie die weitere Umsetzung von Glycerin-Oxidationsprodukten. Die Biooxidation von Glycerin gelang mit Hilfe einer Alditol-Oxidase deren Aktivität gegenüber Glycerin mittels gerichteter Evolution verbessert werden konnte. Die Alditol-Oxidase katalysiert die Oxidation von Glycerin über Glycerinaldehyd bis zur D-Glycerinsäure. Eine Racematspaltung von Glycerinaldehyd wurde mittels einer neu beschriebenen Aldehyd-Dehydrogenase und einem elektrolytischen Cofaktor-Recyclingsystem realisiert. Artikel drei und vier behandeln die Charakterisierung und Protein Engineering von Polyol-Dehydrogenasen. Die Thermostabilität einer bislang unbeschriebenen Polyol-Dehydrogenase wurde mittels rationalem Protein-Design erhöht. Die Cofaktorspezifität des Enzyms konnte mittels ortsgerichteter Mutagenese erweitert werden. Diese thermostabile Polyol-Dehydrogenase konnte mit einer Cyclohexanon-Monooxigenase kombiniert werden, um ε-Caprolacton ausgehend von Cyclohexanol unter Verwendung eines internen Cofaktor-Recyclingsystems zu synthetisieren.

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Author: Hauke Wulf
Title Additional (German):Verwendung und Verbesserung von Oxidoreduktasen für die Biokatalyse
Advisor:Prof. Dr. Uwe Bornscheuer
Document Type:Doctoral Thesis
Date of Publication (online):2013/07/08
Granting Institution:Ernst-Moritz-Arndt-Universität, Mathematisch-Naturwissenschaftliche Fakultät (bis 31.05.2018)
Date of final exam:2013/06/28
Release Date:2013/07/08
GND Keyword:Biokatalyse, Oxidoreductasen, Proteindesign
Faculties:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Chemie und Biochemie
DDC class:500 Naturwissenschaften und Mathematik / 540 Chemie