Immobilization of phenylalanine dehydrogenase onto Eupergit CM for the synthesis of (S)-2-amino-4-phenylbutyric acid

Structure-guided steric hindrance engineering of Bacillus badius phenylalanine dehydrogenase for efficient L-homophenylalanine synthesis

BACKGROUND

Direct reductive amination of prochiral 2-oxo-4-phenylbutyric acid (2-OPBA) catalyzed by phenylalanine dehydrogenase (PheDH) is highly attractive in the synthesis of the pharmaceutical chiral building block L-homophenylalanine (L-HPA) given that its sole expense is ammonia and that water is the only byproduct. Current issues in this field include a poor catalytic efficiency and a low substrate loading.

RESULTS

In this study, we report a structure-guided steric hindrance engineering of PheDH from Bacillus badius to create an enhanced biocatalyst for efficient L-HPA synthesis. Mutagenesis libraries based on molecular docking, double-proximity filtering, and a degenerate codon significantly increased catalytic efficiency. Seven superior mutants were acquired, and the optimal triple-site mutant, V309G/L306V/V144G, showed a 12.7-fold higher k_cat value, and accordingly a 12.9-fold higher k_cat/K_m value, than that of the wild type. A paired reaction system comprising V309G/L306V/V144G and glucose dehydrogenase converted 1.08 M 2-OPBA to L-HPA in 210 min, and the specific space-time conversion was 30.9 mmol g^-1 L^-1 h^-1. The substrate loading and specific space-time conversion are the highest values to date. Docking simulation revealed increases in substrate-binding volume and additional degrees of freedom of the substrate 2-OPBA in the pocket. Tunnel analysis suggested the formation of new enzyme tunnels and the expansion of existing ones.

CONCLUSIONS

Overall, the results show that the mutant V309G/L306V/V144G has the potential for the industrial synthesis of L-HPA. The modified steric hindrance engineering approach can be a valuable addition to the current enzyme engineering toolbox.

Cascaded Biocatalysis and Bioelectrocatalysis: Overview and Recent Advances

Enzyme cascades are plentiful in nature, but they also have potential in artificial applications due to the possibility of using the target substrate in biofuel cells, electrosynthesis, and biosensors. Cascade reactions from enzymes or hybrid bioorganic catalyst systems exhibit extended substrate range, reaction depth, and increased overall performance. This review addresses the strategies of cascade biocatalysis and bioelectrocatalysis for ( a) CO2 fixation, ( b) high value-added product formation, ( c) sustainable energy sources via deep oxidation, and ( d) cascaded electrochemical enzymatic biosensors. These recent updates in the field provide fundamental concepts, designs of artificial electrocatalytic oxidation-reduction pathways (using a flexible setup involving organic catalysts and engineered enzymes), and advances in hybrid cascaded sensors for sensitive analyte detection.

Enzymatic asymmetric synthesis of chiral amino acids

This review summarizes the progress achieved in the enzymatic asymmetric synthesis of chiral amino acids from prochiral substrates.

One-step biosynthesis of α-ketoisocaproate from L-leucine by an Escherichia coli whole-cell biocatalyst expressing an L-amino acid deaminase from Proteus vulgaris

This work aimed to develop a whole-cell biotransformation process for the production of α-ketoisocaproate from L-leucine. A recombinant Escherichia coli strain was constructed by expressing an L-amino acid deaminase from Proteus vulgaris. To enhance α-ketoisocaproate production, the reaction conditions were optimized as follows: whole-cell biocatalyst 0.8 g/L, leucine concentration 13.1 g/L, temperature 35 °C, pH 7.5, and reaction time 20 h. Under the above conditions, the α-ketoisocaproate titer reached 12.7 g/L with a leucine conversion rate of 97.8%. In addition, different leucine feeding strategies were examined to increase the α-ketoisocaproate titer. When 13.1 g/L leucine was added at 2-h intervals (from 0 to 22 h, 12 addition times), the α-ketoisocaproate titer reached 69.1 g/L, while the leucine conversion rate decreased to 50.3%. We have developed an effective process for the biotechnological production of α-ketoisocaproate that is more environmentally friendly than the traditional petrochemical synthesis approach.