Researchers Find New ω-transaminases for Biocatalytic Production of Optically Pure Amines and Unnatural Amino Acids

Nov 03, 2014     Email"> PrintText Size

Chiral amines and unnatural amino acids have been widely used in diverse sectors such as pharmaceutical, chemical, cosmetic, food and agricultural industries. ω-Transaminase (ω-TA), due to its advantages such as high stereoselectivity, rapid reaction rate, broad substrate specificity, and no requirement for external cofactor, has increasingly been used for the production of chiral amines and unnatural amino acids. 

Recently, the researchers from Laboratory of Biocatalysis and Green chemistry of Tianjin Institute of Industrial Biotechnology of Chinese Academy of Sciences identified a new (S)-selective ω-TA ((S)-TA) and five new (R)-selective ω-TAs ((R)-TAs) using in silico method. These enzymes showed unique catalytic properties and may serve as useful catalysts for the production of optically pure amines and unnatural amino acids.   

The (S)-TA HBV from Burkholderia vietnamiensis was found to have a broad substrate profile. Especially, it catalyzed the amino transfer of (S)-1-methylbenzylamine to ethyl acetoacetate, ethyl propionylacetate and levulinic acid to afford the corresponding (S)-configurated amino acids or esters with 99% ee. It was the first time to report that optically pure (S)-3-aminopentanoic acid ethyl ester and (S)-4-aminovaleric acid were produced with transaminase as catalyst.

In the kinetic resolution of racemic amines using HBV as catalyst and glyoxylate as amino acceptor, optically pure amines were obtained.   

The five new (R)-TAs (HFO, HNH, HTA, HTR and HTV) were from Fusarium oxysporum, Nectria haematococca, Trichoderma atroviride, Trichoderma reesei and Trichoderma virens, respectively. The (R)-TAs showed activity toward a series of keto acids and keto esters including pyruvic acid, 2-oxobutyric acid, 2-ketovaleric acid, 3-mercaptopyruvate, ethyl acetoacetate, ethyl propionylacetate and levulinic acid. All of the corresponding products were unnatural amino acids or esters (ee>99%).

The feasibility of (R)-TAs (HFO and HTR) for the kinetic resolution of racemic amines was tested with pyruvate (40 mM) as amino accepter. All the racemic amines (50 mM) tested were successfully resolved and optically pure (S)-enantiomers (ee>99%) were obtained with good conversions. The lyophilized crude cell-free extract of HFO showed high thermostability in organic solvent (ethyl acetate), 95% catalytic activity remained after incubation at 60 °C for 5 h. The lyophilized enzyme powder (HFO) can efficiently catalyze the asymmetric amination in organic solvent.

The research articles entitled “Characterization of (R)-selective amine transaminases identified by in silico motif sequence blast” and “Substrate profile of an ω-transaminase from Burkholderia vietnamiensis and its potential for the production of optically pure amines and unnatural amino acids” were published in Applied Microbiology and Biotechnology and Journal of Molecular Catalysis B: Enzymatic. Two Chinese patents were applied (201310556932.X and 201310556825.7).

This research were supported by the National Basic Research Program of China (973 Program, No. 2011CB710801), National Natural Science Foundation of China (grant no. 21072151) and the CAS Special Grant for Postgraduate Research, Innovation and Practice (grant no. Y2J8041021).