Ala258Phe substitution in Bacillus sp. YX-1 glucose dehydrogenase improves its substrate preference for xylose

NAD(P)-Dependent Glucose Dehydrogenases: Underestimated Multifunctional Biocatalysts

The last decade has witnessed tremendous progress in the field of biocatalysis. One of the most frequently utilized enzymes in diverse biocatalytic applications is NAD(P)-dependent glucose dehydrogenases (GDHs). Traditionally, these enzymes are employed for their role in regenerating NAD(P)H in various enzymatic reactions utilizing glucose. However, recent studies have expanded the scope of GDHs beyond cofactor regeneration, highlighting their potential as biocatalysts in diverse chemical transformations. GDHs have demonstrated versatility in catalyzing key reactions in the synthesis of various drug molecules and intermediates, including ketone reduction to produce alcohols, imine reduction of C=N bonds to yield amines, reduction of aldehydes to alcohols, and dehydrogenation of cyclohexanol derivatives. This review highlights recent advancements in elucidating the multifunctional roles of NAD(P)-dependent glucose dehydrogenases (GDHs) in biocatalysis, with an emphasis on their growing applications and significant potential in small molecule synthesis.

Modification of an engineered Escherichia coli by a combinatorial strategy to improve 3,4-dihydroxybutyric acid production

OBJECTIVES

3,4-Dihydroxybutyric acid (3,4-DHBA) is a multifunctional C4 platform compound widely used for the synthesis of various materials, including pharmaceuticals. Although, a biosynthetic pathway for 3,4-DHBA production has been developed, its low yield still precludes large-scale use. Here, a heterologous four-step biosynthetic pathway was established in recombinant Escherichia coli (E. coli) using a combinatorial strategy.

RESULTS

Several aldehyde dehydrogenases (ALDHs) were screened, using in vitro enzyme assays, to identify suitable catalysts for the dehydrogenation of 3,4-dihydroxybutanal (3,4-DHB) to 3,4-DHBA. A pathway containing glucose dehydrogenase (BsGDH) from Bacillus subtilis, D-xylonate dehydratase (YagF) from E. coli, benzoylformate decarboxylase (PpMdlC) from Pseudomonas putida and ALDH was introduced into E. coli, generating 3.04 g/L 3,4-DHBA from D-xylose (0.190 g 3,4-DHBA/g D-xylose). Disruption of competing pathways by deleting xylA, ghrA, ghrB and adhP contributed to an 87% increase in 3,4-DHBA accumulation. Expression of a fusion construct containing PpMdlC and YagF enhanced the 3,4-DHBA titer, producing the highest titer and yield reported thus far (7.71 g/L; 0.482 g 3,4-DHBA/g D-xylose).

CONCLUSIONS

These results showed that deleting genes from competing pathways and constructing fusion proteins significantly improved the titer and yield of 3,4-DHBA in engineered E. coli.

Efficient production of (S)-1-phenyl-1,2-ethanediol using xylan as co-substrate by a coupled multi-enzyme Escherichia coli system

Background

(S)-1-phenyl-1,2-ethanediol is an important chiral intermediate in the synthesis of liquid crystals and chiral biphosphines. (S)-carbonyl reductase II from Candida parapsilosis catalyzes the conversion of 2-hydroxyacetophenone to (S)-1-phenyl-1,2-ethanediol with NADPH as a cofactor. Glucose dehydrogenase with a Ala258Phe mutation is able to catalyze the oxidation of xylose with concomitant reduction of NADP⁺ to NADPH, while endo-β-1,4-xylanase 2 catalyzes the conversion of xylan to xylose. In the present work, the Ala258Phe glucose dehydrogenase mutant and endo-β-1,4-xylanase 2 were introduced into the (S)-carbonyl reductase II-mediated chiral pathway to strengthen cofactor regeneration by using xylan as a naturally abundant co-substrate.

Results

We constructed several coupled multi-enzyme systems by introducing (S)-carbonyl reductase II, the A258F glucose dehydrogenase mutant and endo-β-1,4-xylanase 2 into Escherichia coli. Different strains were produced by altering the location of the encoding genes on the plasmid. Only recombinant E. coli/pET-G-S-2 expressed all three enzymes, and this strain produced (S)-1-phenyl-1,2-ethanediol from 2-hydroxyacetophenone as a substrate and xylan as a co-substrate. The optical purity was 100% and the yield was 98.3% (6 g/L 2-HAP) under optimal conditions of 35 °C, pH 6.5 and a 2:1 substrate-co-substrate ratio. The introduction of A258F glucose dehydrogenase and endo-β-1,4-xylanase 2 into the (S)-carbonyl reductase II-mediated chiral pathway caused a 54.6% increase in yield, and simultaneously reduced the reaction time from 48 to 28 h.

Conclusions

This study demonstrates efficient chiral synthesis using a pentose as a co-substrate to enhance cofactor regeneration. This provides a new approach for enantiomeric catalysis through the inclusion of naturally abundant materials.