Eun-Yeong Jeon

Multistep Enzymatic Synthesis of Long-Chain α,ω-Dicarboxylic and ω-Hydroxycarboxylic Acids from Renewable Fatty Acids and Plant Oils†

A multistep enzyme catalysis was successfully implemented to produce long-chain α,ω-dicarboxylic and ω-hydroxycarboxylic acids from renewable fatty acids and plant oils. Sebacic acid as well as ω-hydroxynonanoic acid and ω-hydroxytridec-11-enoic acid were produced from oleic and ricinoleic acid.

Engineering of Baeyer-Villiger monooxygenase-based Escherichia coli biocatalyst for large scale biotransformation of ricinoleic acid into (Z)-11-(heptanoyloxy)undec-9-enoic acid

Baeyer-Villiger monooxygenases (BVMOs) are able to catalyze regiospecific Baeyer-Villiger oxygenation of a variety of cyclic and linear ketones to generate the corresponding lactones and esters, respectively. However, the enzymes are usually difficult to express in a functional form in microbial cells and are rather unstable under process conditions hindering their large-scale applications. Thereby, we investigated engineering of the BVMO from Pseudomonas putida KT2440 and the gene expression system to improve its activity and stability for large-scale biotransformation of ricinoleic acid (1) into the ester (i.e., (Z)-11-(heptanoyloxy)undec-9-enoic acid) (3), which can be hydrolyzed into 11-hydroxyundec-9-enoic acid (5) (i.e., a precursor of polyamide-11) and n-heptanoic acid (4). The polyionic tag-based fusion engineering of the BVMO and the use of a synthetic promoter for constitutive enzyme expression allowed the recombinant Escherichia coli expressing the BVMO and the secondary alcohol dehydrogenase of Micrococcus luteus to produce the ester (3) to 85 mM (26.6 g/L) within 5 h. The 5 L scale biotransformation process was then successfully scaled up to a 70 L bioreactor; 3 was produced to over 70 mM (21.9 g/L) in the culture medium 6 h after biotransformation. This study demonstrated that the BVMO-based whole-cell reactions can be applied for large-scale biotransformations.

Expression levels of chaperones influence biotransformation activity of recombinant Escherichia coli expressing Micrococcus luteus alcohol dehydrogenase and Pseudomonas putida Baeyer–Villiger monooxygenase

We demonstrated for the first time that the archaeal chaperones (i.e., γ‐prefoldin and thermosome) can stabilize enzyme activity in vivo. Ricinoleic acid biotransformation activity of recombinant Escherichia coli expressing Micrococcus luteus alcohol dehydrogenase and the Pseudomonas putida KT2440 Baeyer–Villiger monooxygenase improved significantly with co‐expression of γ‐prefoldin or recombinant themosome originating from the deep‐sea hyperthermophile archaea Methanocaldococcus jannaschii. Furthermore, the degree of enhanced activity was dependent on the expression levels of the chaperones. For example, whole‐cell biotransformation activity was highest at 12 µmol/g dry cells/min when γ‐prefoldin expression level was approximately 46% of the theoretical maximum. This value was approximately two‐fold greater than that in E. coli, where the γ‐prefoldin expression level was zero or set to the theoretical maximum. Therefore, it was assumed that the expression levels of chaperones must be optimized to achieve maximum biotransformation activity in whole‐cell biocatalysts. Biotechnol. Bioeng. 2015;112: 889–895.

Intracellular transformation rates of fatty acids are influenced by expression of the fatty acid transporter FadL in Escherichia coli cell membrane

Fatty acids have a low permeability through the cell membrane. Therefore, the intracellular biotransformation of fatty acids can be slow due to supply limitations. The effects of expression level of the fatty acid transporter FadL in Escherichia coli on the biotransformations were investigated. The enhanced expression of FadL led to 5.5-fold increase of the maximum reaction rate Vmax (i.e., 200 μmol/min per g dry cells (200 U/g dry cells)) of the recombinant E. coli expressing a hydratase of Stenotrophomonas maltophilia in the periplasm with respect to hydration of oleic acid. The FadL expression level was also critical for oxidation of 12- and 10- hydroxyoctadecanoic acid by the recombinant E. coli expressing an alcohol dehydrogenase (ADH) of Micrococcus luteus. In addition, the multistep biotransformation of ricinoleic acid into the ester (i.e., (Z)-11-(heptanoyloxy)undec-9-enoic acid) by the recombinant E. coli expressing the ADH of M. luteus and a Baeyer-Villiger monooxygenase of Pseudomonas putida KT2440 was 2-fold increased to 40 U/g dry cells with expression of FadL to an appropriate level. The FadL expression level is one of the critical factors to determine whole-cell biotransformation rates of not only long chain fatty acids but also hydroxy fatty acids. This study may contribute to whole-cell biocatalyst engineering for biotransformation of hydrophobic substances.

Improving catalytic activity of the Baeyer–Villiger monooxygenase-based Escherichia coli biocatalysts for the overproduction of (Z)-11-(heptanoyloxy)undec-9-enoic acid from ricinoleic acid

Baeyer–Villiger monooxygenases (BVMOs) can be used for the biosynthesis of lactones and esters from ketones. However, the BVMO-based biocatalysts are not so stable under process conditions. Thereby, this study focused on enhancing stability of the BVMO-based biocatalysts. The biotransformation of ricinoleic acid into (Z)-11-(heptanoyloxy)undec-9-enoic acid by the recombinant Escherichia coli expressing the BVMO from Pseudomonas putida and an alcohol dehydrogenase from Micrococcus luteus was used as a model system. After thorough investigation of the key factors to influence stability of the BVMO, Cys302 was identified as an engineering target. The substitution of Cys302 to Leu enabled the engineered enzyme (i.e., E6BVMOC302L) to become more stable toward oxidative and thermal stresses. The catalytic activity of E6BVMOC302L-based E. coli biocatalysts was also greater than the E6BVMO-based biocatalysts. Another factor to influence biocatalytic performance of the BVMO-based whole-cell biocatalysts was availability of carbon and energy source during biotransformations. Glucose feeding into the reaction medium led to a marked increase of final product concentrations. Overall, the bioprocess engineering to improve metabolic stability of host cells in addition to the BVMO engineering allowed us to produce (Z)-11-(heptanoyloxy)undec-9-enoic acid to a concentration of 132 mM (41 g/L) from 150 mM ricinoleic acid within 8 h.