A novel and thermostable phenylalanine dehydrogenase for efficient synthesis of bulky aromatic amino acids and derivatives

Phenylalanine dehydrogenases (PDHs) play an important role in pharmaceutical and fine chemical industries due to their ability to produce primary amines via asymmetrically reductive amination. However, the industrial application of PDHs are often limited by their undesirable stability, narrow substrate specificity, especially for unnatural substrates. Here, a novel PDH from Quasibacillus thermotolerans (QtPDH) was identified by gene mining using BbPDH from Bacillus badius as a probe. QtPDH exhibits prominent thermal stability, specifically a half-life of 23 days at 30 °C and pH 8.5, about 300 times longer than that of BbPDH. QtPDH could catalyze various phenylpyruvate analogues, including ethyl 2-oxo-4-phenylbutyrate and l-phenylglycinol, as well as bulky 3-(naphthalen-1-yl)-2-oxopropanoic acid with a reductive amination specific activity of 1.90 U·mg–1. Catalyzed by QtPDH in couple with BmGDH, efficient production of 2‑chloro-l-phenylalanine was achieved at 1.0 M 3-(2-chlorophenyl)-2-oxopropionic acid with > 99 % conversion, 99 % ee, and space-time yield of 30.46 g·L–1·h–1. Our results suggest that this newly identified QtPDH features high catalytic efficiency and thermostability, and is a promising biocatalyst for the industrial productions of bulky aromatic primary amines.