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Marine algae produce complex polysaccharides, which can be degraded by marine heterotrophic bacteria utilizing carbohydrate-active enzymes. The red algal polysaccharide porphyran contains the methoxy sugar 6-O-methyl-D-galactose (G6Me). In the degradation of porphyran, oxidative demethylation of this monosaccharide towards D-galactose and formaldehyde occurs, which is catalyzed by a cytochrome P450 monooxygenase and its redox partners. In direct proximity to the genes encoding for the key enzymes of this oxidative demethylation, genes encoding for zinc-dependent alcohol dehydrogenases (ADHs) were identified, which seem to be conserved in porphyran utilizing marine Flavobacteriia. Considering the fact that dehydrogenases could play an auxiliary role in carbohydrate degradation, we aimed to elucidate the physiological role of these marine ADHs. Although our results reveal that the ADHs are not involved in formaldehyde detoxification, a knockout of the ADH gene causes a dramatic growth defect of Zobellia galactanivorans with G6Me as a substrate. This indicates that the ADH is required for G6Me utilization. Complete biochemical characterizations of the ADHs from Formosa agariphila KMM 3901T (FoADH) and Z. galactanivorans DsijT (ZoADH) were performed, and the substrate screening revealed that these enzymes preferentially convert aromatic aldehydes. Additionally, we elucidated the crystal structures of FoADH and ZoADH in complex with NAD+ and showed that the strict substrate specificity of these new auxiliary enzymes is based on a narrow active site.
This thesis deals with the process considerations and optimizations of a whole-cell enzyme cascade reaction for the synthesis of ɛ-caprolactone. The enzyme cascade synthesis of ɛ-caprolactone has been conceptualized and verified using a dehydrogenase and a monooxygenase. The advantage of this enzyme combination is the closed-loop co-factor regeneration. Dehydrogenase and monooxygenase expressed in discrete whole cells were applied in defined ratio to conceptualize the cascade reaction. This necessitates the use of separate co-factor regeneration system due to impermeability of the E. coli cell wall to the co-factor. Article I deal with the design and optimization of dehydrogenase and monooxygenase co-expression in a same E. coli cell. In Article II, the cascade reaction was upscaled and a fed-batch process was realized. Following which, the important reaction metrices were analyzed and optimized. Article III extends the two-enzyme cascade with a lipase. The use of lipase helps to overcome the product inhibition of monooxygenase by ɛ-caprolactone.