Amine donor and acceptor influence on the thermodynamics of ω-transaminase reactions

Engineering of ω-transaminase at binding pocket and access tunnel for preparation of (R)-1-phenoxypropan-2-amine

Transaminase-catalyzed amination of prochiral ketones is regarded as a promising route for optically active amines production. These chiral amines serve as key building blocks in the synthesis of agrochemicals and pharmaceuticals. However, the limited substrate scope and substrate/(co)product inhibition have significantly hindered the industrial-scale implementation of transaminase-catalyzed processes. Engineering of TAs at binding sites is an efficient strategy to expand the capacity of binding pocket, thereby improving the catalytic efficiency. Furthermore, modification of access tunnel is crucial for adjusting the transfer efficiency of ligand. In this endeavor, we engineered an ω-TA from Nocardioides sp. CER19(NsTA) at binding sites and access tunnel, and applied the mutants for enantioselective synthesis of (R)-1-phenoxypropan-2-amine. Mutation at residues H62 and Y122 increased catalytic activity of the TA towards 1-phenoxyacetone, the optimal mutants NsTAH62A and NsTAY122A with improved enzyme activity was obtained, which was 2.0 and 1.5-fold higher than that of the wild-type NsTA respectively. This allowed completely conversion of 5 mM 1-phenoxyacetone to (R)-1-phenoxypropan-2-amine at 4 h and > 99 % ee (in comparison to 66 % convesion with the wild-type NsTA). Molecular dynamic simulation suggested improved flexibility of NsTAH62A, which may result in eliminating of substrate inhibition. While mutant NsTAD7 (with deletion of 7 amino acids at N-terminal) exhibited about 1.6-fold increase of conversion. Tunnel analysis suggested that reshaping of the tunnel entrance may alter the shape and size of the tunnel, which might promote the release of the products. These results of our study lay the foundation for enantioselective synthesis of (R)-1-phenoxypropan-2-amine and provide a promising engineering strategy to enhance the activity of TAs and overcome substrate/(co)product inhibition of ω-TA towards bulky substrates.

Advances in biosynthesis of chiral amide herbicides and the key enzymes: dimethenamid-P and S-metolachlor as case studies

Chiral amide herbicides represent a significant class of agrochemicals, widely used for effective weed control. Prominent examples include S-metolachlor and dimethenamid-P, both of which share the intermediate (S)-1-methoxy-2-propylamine, a key structural component in their synthesis. Developing green and sustainable methods for producing this intermediate is crucial for enhancing the environmental and economic feasibility of herbicide manufacturing. Biosynthesis, with its advantages in sustainability and efficiency, has emerged as a pivotal approach in pesticide production. This review explores the classification and current development status of chiral amide herbicides, including their varieties and applications in the agricultural market. It outlines the synthesis pathways for S-metolachlor and dimethenamid-P, covering both chemical and biosynthetic routes. The review also highlights the functional properties of the key enzymes involved in the biosynthesis of (S)-1-methoxy-2-propylamine, focusing on the potential for enzyme engineering and creation to optimize these pathways. The challenges and future development directions for amide herbicides are discussed, with an emphasis on overcoming synthetic and ecological barriers.

Development of a Thermodynamically Favorable Multi-enzyme Cascade Reaction for Efficient Sustainable Production of ω-Amino Fatty Acids and α,ω-Diamines

Aliphatic ω-amino fatty acids (ω-AFAs) and α,ω-diamines (α,ω-DMs) are essential monomers for the production of nylons. Development of a sustainable biosynthesis route for ω-AFAs and α,ω-DMs is crucial in addressing the challenges posed by climate change. Herein, we constructed an unprecedented thermodynamically favorable multi-enzyme cascade (TherFavMEC) for the efficient sustainable biosynthesis of ω-AFAs and α,ω-DMs from cheap α,ω-dicarboxylic acids (α,ω-DAs). This TherFavMEC was developed by incorporating bioretrosynthesis analysis tools, reaction Gibbs free energy calculations, thermodynamic equilibrium shift strategies and cofactor (NADPH&ATP) regeneration systems. The molar yield of 6-aminohexanoic acid (6-ACA) from adipic acid (AA) was 92.3 %, while the molar yield from 6-ACA to 1,6-hexanediamine (1,6-HMD) was 96.1 %, which were significantly higher than those of previously reported routes. Furthermore, the biosynthesis of ω-AFAs and α,ω-DMs from 20.0 mM α,ω-DAs (C6-C9) was also performed, giving 11.2 mM 1,6-HMD (56.0 % yield), 14.8 mM 1,7-heptanediamine (74.0 % yield), 17.4 mM 1,8-octanediamine (87.0 % yield), and 19.7 mM 1,9-nonanediamine (98.5 % yield), respectively. The titers of 1,9-nonanediamine, 1,8-octanediamine, 1,7-heptanediamine and 1,6-HMD were improved by 328-fold, 1740-fold, 87-fold and 3.8-fold compared to previous work. Therefore, this work holds great potential for the bioproduction of ω-AFAs and α,ω-DMs.

Engineered repeat proteins as scaffolds to assemble multi-enzyme systems for efficient cell-free biosynthesis

Multi-enzymatic cascades with enzymes arranged in close-proximity through a protein scaffold can trigger a substrate channeling effect, allowing for efficient cofactor reuse with industrial potential. However, precise nanometric organization of enzymes challenges the design of scaffolds. In this study, we create a nanometrically organized multi-enzymatic system exploiting engineered Tetrapeptide Repeat Affinity Proteins (TRAPs) as scaffolding for biocatalysis. We genetically fuse TRAP domains and program them to selectively and orthogonally recognize peptide-tags fused to enzymes, which upon binding form spatially organized metabolomes. In addition, the scaffold encodes binding sites to selectively and reversibly sequester reaction intermediates like cofactors via electrostatic interactions, increasing their local concentration and, consequently, the catalytic efficiency. This concept is demonstrated for the biosynthesis of amino acids and amines using up to three enzymes. Scaffolded multi-enzyme systems present up to 5-fold higher specific productivity than the non-scaffolded ones. In-depth analysis suggests that channeling of NADH cofactor between the assembled enzymes enhances the overall cascade throughput and the product yield. Moreover, we immobilize this biomolecular scaffold on solid supports, creating reusable heterogeneous multi-functional biocatalysts for consecutive operational batch cycles. Our results demonstrate the potential of TRAP-scaffolding systems as spatial-organizing tools to increase the efficiency of cell-free biosynthetic pathways.

Chiral Synthesis of 3-Amino-1-phenylbutane by a Multi-Enzymatic Cascade System

Asymmetric synthesis of chiral amines from prochiral ketones using transaminases is an attractive biocatalytic strategy. Nevertheless, it is hampered by its unfavorable thermodynamic equilibrium. In the present work, an insitu by-product removal strategy was applied for the synthesis of 3-amino-1-phenylbutane (3-APB) by coupling a transaminase with a pyruvate decarboxylase (PDC), which does not require the use of any expensive additional cofactor. Using this strategy, the pyruvate obtained in the transamination reaction is transformed by PDC into acetaldehyde and CO2 which are of high volatility. Two different transaminases from Chromobacterium violaceum (CviTA) and Vibrio fluvialis (VflTA) were characterized to find out the appropriate pH conditions. In both cases, the addition of PDC dramatically enhanced 3-APB synthesis. Afterwards, different reaction conditions were tested to improve reaction conversion and yield. It was concluded that 30 °C and a 20-fold alanine excess lead to the best process metrics. Under the mentioned conditions, yields higher than 60% were reached with nearly 90% selectivity using both CviTA and VflTA. Moreover, high stereoselectivity for (S)-3-APB was obtained and ee of around 90% was achieved in both cases. For the first time, the asymmetric synthesis of 3-APB using PDC as by-product removal system using CviTA is reported.

Investigating Pervaporation for In Situ Acetone Removal as Process Intensification Tool in ω-Transaminase Catalyzed Chiral Amine Synthesis

Hydrophobic pervaporation (PV), allowing for the separation of an organic component from an aqueous stream, was investigated for in situ acetone removal from a transamination reaction. A poly(dimethylsiloxane) membrane was applied in a coupled enzymatic process at 5 L scale. Among the four components, there was no loss of donor and product amines through PV which was highly desirable. However, in addition to removal of acetone, there was also an unwanted loss of acetophenone (substrate ketone) because of PV. The coupled enzyme-PV process resulted in 13% more product formation compared to the control process (where no PV was applied) after 9 h. Results from a qualitative simulation study (based on partial vapor pressures and a vapor-liquid equilibrium of the feed solution) indicated that PV might have an advantage over direct distillation strategy for selective removal of acetone from the reaction medium. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2731, 2019.

Transaminases for chiral amine synthesis

Amine transaminases are important biocatalysts for the synthesis of chiral primary amines. Unlike many enzymes that have been employed for the synthesis of optically active amines, amine transaminases are capable of asymmetric synthesis and do not rely on costly cofactors that must be regenerated in situ. However, their application as general catalysts for the preparation of amines is hampered by a limited substrate scope, substrate and (co)product inhibition and difficulties associated with displacing challenging reaction equilibrium. There has been important progress made to overcome these challenges, including the development of enzymes with broader substrate scope and the design of methodology to effectively displace the reaction equilibrium. Amine transaminases are also being applied in an increasing range of (chemo)enzymatic cascades and immobilized for applications in flow.

A highly efficient one-enzyme protocol using ω-transaminase and an amino donor enabling equilibrium displacement assisted by molecular oxygen

A highly efficient one-enzyme procedure using ω-transaminase promoted by molecular oxygen for preparing high enantiomeric purity chiral amines was described.

Development of in situ product removal strategies in biocatalysis applying scaled-down unit operations

An experimental platform based on scaled-down unit operations combined in a plug-and-play manner enables easy and highly flexible testing of advanced biocatalytic process options such as in situ product removal (ISPR) process strategies. In such a platform, it is possible to compartmentalize different process steps while operating it as a combined system, giving the possibility to test and characterize the performance of novel process concepts and biocatalysts with minimal influence of inhibitory products. Here the capabilities of performing process development by applying scaled-down unit operations are highlighted through a case study investigating the asymmetric synthesis of 1-methyl-3-phenylpropylamine (MPPA) using ω-transaminase, an enzyme in the sub-family of amino transferases (ATAs). An on-line HPLC system was applied to avoid manual sample handling and to semi-automatically characterize ω-transaminases in a scaled-down packed-bed reactor (PBR) module, showing MPPA as a strong inhibitor. To overcome the inhibition, a two-step liquid-liquid extraction (LLE) ISPR concept was tested using scaled-down unit operations combined in a plug-and-play manner. Through the tested ISPR concept, it was possible to continuously feed the main substrate benzylacetone (BA) and extract the main product MPPA throughout the reaction, thereby overcoming the challenges of low substrate solubility and product inhibition. The tested ISPR concept achieved a product concentration of 26.5 g_MPPA  · L^-1 , a purity up to 70% g_MPPA  · g_tot^-1 and a recovery in the range of 80% mol · mol^-1 of MPPA in 20 h, with the possibility to increase the concentration, purity, and recovery further. Biotechnol. Bioeng. 2017;114: 600-609. © 2016 Wiley Periodicals, Inc.