Characterization and Catalytic-Site-Analysis of an Aldo-Keto Reductase with Excellent Solvent Tolerance

Identification and functional characterization of a novel aldo-keto reductase from Aloe vera

MAIN CONCLUSION

The present investigation profoundly asserted the catalytic potential of plant-based aldo-ketoreductase, postulating its role in polyketide biosynthesis and providing new insights for tailored biosynthesis of vital plant polyketides for therapeutics. Plants hold great potential as a future source of innovative biocatalysts, expanding the possibilities within chemical reactions and generating a variety of benefits. The aldo-keto reductase (AKR) superfamily includes a huge collection of NAD(P)H-dependent oxidoreductases that carry out a variety of redox reactions essential for biosynthesis, detoxification, and intermediary metabolism. The present study involved the isolation, cloning, and purification of a novel aldo-ketoreductase (AvAKR) from the leaves of Aloe vera (Aloe barbadensis Miller) by heterologous gene expression in Escherichia coli based on the unigene sequences of putative ketoreductase and cDNA library screening by oligonucleotide hybridization. The in-silico structural analysis, phylogenetic relationship, and molecular modeling were outranged to approach the novelty of the sequence. Additionally, agroinfiltration of the candidate gene tagged with a green fluorescent protein (GFP) was employed for transient expression in the Nicotiana benthamiana to evaluate the sub-cellular localization of the candidate gene. The AvAKR preferred cytoplasmic localization and shared similarities with the known plant AKRs, keeping the majority of the conserved active-site residues in the AKR superfamily enzymes. The enzyme facilitated the NADPH-dependent reduction of various carbonyl substrates, including benzaldehyde and sugars, proclaiming a broad spectrum range. Our study successfully isolated and characterized a novel aldo-ketoreductase (AvAKR) from Aloe vera, highlighting its versatile NADPH-dependent carbonyl reduction proficiency therewith showcasing its potential as a versatile biocatalyst in diverse redox reactions.

Biosynthesis of (S)-1-(1-naphthyl) ethanol by microbial ketoreductase

(S)-1-(1-naphthyl) ethanol (SNE) is a chiral drug intermediate for the production of mevinic acid analog, a potent cholesterol agent. It acts as an HMG-CoA reductase inhibitor and is hence used in the synthesis of statins. Statins are lipid-lowering drugs used to lower cholesterol in the body. In our present study, we carried out whole-cell bioreduction of 1-Acetonaphthone to enantiopure SNE using selected microorganisms acquired by soil acclimation technique. The microorganism which exhibited higher bioreduction activity was determined using high-performance liquid chromatography (HPLC), and it was identified as Pichia kudriavzevii by ITS primer sequencing. After optimizing the parameters, Pichia sp. produced SNE with good conversion (75%), yield (67%), and excellent enantiomeric excess (100%). The microbial enzyme showed higher activity at 24-h-old supernatant. The crude and partially purified enzyme exhibited a specific activity of 51.13 U/mL and 62.72 U/mL, respectively, with a 1.22 purification fold.

Semirational engineering of an aldo-keto reductase KmAKR for overcoming trade-offs between catalytic activity and thermostability

Enzyme engineering usually generates trade-offs between activity, stability, and selectivity. Herein, we report semirational engineering of an aldo-keto reductase (AKR) KmAKR for simultaneously enhancing its thermostability and catalytic activity. Previously, we constructed KmAKR_M9 (W297H/Y296W/K29H/Y28A/T63M/A30P/T302S/N109K/S196C), which showed outstanding activity towards t-butyl 6-chloro-(3R,5S)-dihydroxyhexanoate ((3R,5S)-CDHH), and t-butyl 6-cyano-(3R,5R)-dihydroxyhexanoate, the key chiral building blocks of rosuvastatin and atorvastatin. Under the guidance of computer-aided design including consensus residues analysis and molecular dynamics (MD) simulations, K164, S182, S232, and Q266 were dug out for their thermostability conferring roles, generating the "best" mutant KmAKR_M13 (W297H/Y296W/K29H/Y28A/T63M/A30P/T302S/N109K/S196C/K164E/S232A/S182H/Q266D). The T_m and T₅₀ ¹⁵ values of KmAKR_M13 were 10.4 and 6.1°C higher than that of KmAKR_M9 , respectively. Moreover, it displayed a significantly elevated organic solvent tolerance over KmAKR_M9 . Structural analysis indicated that stabilization of the α-helixes mainly contributed to thermostability enhancement. Under the optimized conditions, KmAKR_M13 completely asymmetrically reduced 400 g/l t-butyl 6-chloro-(5S)-hydroxy-3-oxohexanoate ((5S)-CHOH) in 8.0 h at a high substrate to catalyst ratio (S/C) of 106.7 g/g, giving diastereomerically pure (3R,5S)-CDHH (>99.5% d.e._P ) with a space-time yield (STY) of 449.2 g/l·d.