AUTHOR=Tong Feifei , Qin Zongmin , Wang Hongyue , Jiang Yingying , Li Junkuan , Ming Hui , Qu Ge , Xiao Yazhong , Sun Zhoutong TITLE=Biosynthesis of Chiral Amino Alcohols via an Engineered Amine Dehydrogenase in E. coli JOURNAL=Frontiers in Bioengineering and Biotechnology VOLUME=9 YEAR=2022 URL=https://www.frontiersin.org/journals/bioengineering-and-biotechnology/articles/10.3389/fbioe.2021.778584 DOI=10.3389/fbioe.2021.778584 ISSN=2296-4185 ABSTRACT=

Chiral amino alcohols are prevalent synthons in pharmaceuticals and synthetic bioactive compounds. The efficient synthesis of chiral amino alcohols using ammonia as the sole amino donor under mild conditions is highly desired and challenging in organic chemistry and biotechnology. Our previous work explored a panel of engineered amine dehydrogenases (AmDHs) derived from amino acid dehydrogenase (AADH), enabling the one-step synthesis of chiral amino alcohols via the asymmetric reductive amination of α-hydroxy ketones. Although the AmDH-directed asymmetric reduction is in a high stereoselective manner, the activity is yet fully excavated. Herein, an engineered AmDH derived from a leucine dehydrogenase from Sporosarcina psychrophila (SpAmDH) was recruited as the starting enzyme, and the combinatorial active-site saturation test/iterative saturation mutagenesis (CAST/ISM) strategy was applied to improve the activity. After three rounds of mutagenesis in an iterative fashion, the best variant wh84 was obtained and proved to be effective in the asymmetric reductive amination of 1-hydroxy-2-butanone with 4-fold improvements in kcat/Km and total turnover number (TTN) values compared to those of the starting enzyme, while maintaining high enantioselectivity (ee >99%) and thermostability (T5015 >53°C). In preparative-scale reaction, the conversion of 100 and 200 mM 1-hydroxy-2-butanone catalyzed by wh84 was up to 91–99%. Insights into the source of an enhanced activity were gained by the computational analysis. Our work expands the catalytic repertoire and toolbox of AmDHs.