Pichia stipitis OYE 2.6 variants with improved catalytic efficiencies from site-saturation mutagenesis libraries

Purification and biochemical characterization of a novel ene- reductase from Kazachstania exigua HSC6 for dihydro-β-ionone from β-ionone

PURPOSE

We purified and characterized a novel ene-reductase (KaDBR1) from Kazachstania exigua HSC6 for the synthesis of dihydro-β-ionone from β-ionone.

METHODS

KaDBR1 was purified to homogeneity by ammonium sulfate precipitation and phenyl-Sepharose Fast Flow and Q-Sepharose chromatography. The purified enzyme was characterized by measuring the amount of dihydro-β-ionone from β-ionone with LC-MS analysis method.

RESULTS

The molecular mass of KaDBR1 was estimated to be 45 kDa by SDS-PAGE. The purified KaDBR1 enzyme had optimal activity at 60 °C and pH 6.0. The addition of 5 mM Mg²⁺, Ca²⁺, Al³⁺, Na⁺, and dithiothreitol increased the activity of KaDBR1 by 25%, 18%, 34%, 20%, and 23%, respectively. KaDBR1 favored NADH over NADPH as a cofactor, and its catalytic efficiency (kcat/Km) toward β-ionone using NADH was 8.1-fold greater than when using NADPH.

CONCLUSION

Owing to its unique properties, KaDBR1 is a potential candidate for the enzymatic biotransformation of β-ionone to dihydro-β-ionone in biotechnology applications.

Semi-rational protein engineering of a novel ene-reductase from Galdieria sulphuraria for asymmetric reduction of (R)-carvone and ketoisophorone

Asymmetric reduction of (R)-carvone and ketoisophorone by an engineered ene-reductase from Galdieria sulphuraria (GsOYE) combined with glucose dehydrogenase for NADPH regeneration were studied. A semi-rational protein engineering was used to enhance the activity and selectivity of GsOYE. Upon the sequence alignment and molecular docking results, two amino acid residues at positions 66 and 270 were selected as saturation mutation sites. Finally, a single substitution variant of GsOYE-N270A with complete conversion (100%) and diastereoselectivity (de_p >99%) for reduction of (R)-carvone and a double substitution variant GsOYE-Y66P/N270H with improved stereoselectivity for reduction of ketoisophorone were obtained. This article is protected by copyright. All rights reserved.

Discovery, Characterisation, Engineering and Applications of Ene Reductases for Industrial Biocatalysis

Recent studies of multiple enzyme families collectively referred to as ene-reductases (ERs) have highlighted potential industrial application of these biocatalysts in the production of fine and speciality chemicals. Processes have been developed whereby ERs contribute to synthetic routes as isolated enzymes, components of multi-enzyme cascades, and more recently in metabolic engineering and synthetic biology programmes using microbial cell factories to support chemicals production. The discovery of ERs from previously untapped sources and the expansion of directed evolution screening programmes, coupled to deeper mechanistic understanding of ER reactions, have driven their use in natural product and chemicals synthesis. Here we review developments, challenges and opportunities for the use of ERs in fine and speciality chemicals manufacture. The ER research field is rapidly expanding and the focus of this review is on developments that have emerged predominantly over the last 4 years.

Investigating Saccharomyces cerevisiae alkene reductase OYE 3 by substrate profiling, X-ray crystallography and computational methods

Saccharomyces cerevisiae OYE 3 and OYE 1 share 80% sequence identity, but sometimes differ in stereoselectivities.

Revealing Additional Stereocomplementary Pairs of Old Yellow Enzymes by Rational Transfer of Engineered Residues

Every year numerous protein engineering and directed evolution studies are published, increasing the knowledge that could be used by protein engineers. Here we test a protein engineering strategy that allows quick access to improved biocatalysts with very little screening effort. Conceptually it is assumed that engineered residues previously identified by rational and random methods induce similar improvements when transferred to family members. In an application to ene-reductases from the Old Yellow Enzyme (OYE) family, the newly created variants were tested with three compounds, revealing more stereocomplementary OYE pairs with potent turnover frequencies (up to 660 h^-1 ) and excellent stereoselectivities (up to >99 %). Although systematic prediction of absolute enantioselectivity of OYE variants remains a challenge, "scaffold sampling" was confirmed as a promising addition to protein engineers' collection of strategies.

Characterization of an ene-reductase from Meyerozyma guilliermondii for asymmetric bioreduction of α,β-unsaturated compounds

OBJECTIVES

To characterize a novel ene-reductase from Meyerozyma guilliermondii and achieve the ene-reductase-mediated reduction of activated C=C bonds.

RESULTS

The gene encoding an ene-reductase was cloned from M. guilliermondii. Sequence homology analysis showed that MgER shared the maximal amino acid sequence identity of 57 % with OYE2.6 from Scheffersomyces stipitis. MgER showed the highest specific activity at 30 °C and pH 7 (100 mM sodium phosphate buffer), and excellent stereoselectivities were achieved for the reduction of (R)-carvone and ketoisophorone. Under the reaction conditions (30 °C and pH 7.0), 150 mM (R)-carvone could be completely converted to (2R,5R)-dihydrocarvone within 22 h employing purified MgER as catalyst, resulting in a yield of 98.9 % and an optical purity of >99 % d.e.

CONCLUSION

MgER was characterized as a novel ene-reductase from yeast and showed great potential for the asymmetric reduction of activated C=C bonds of α,β-unsaturated compounds.