Characterization of the stability of Vibrio fluvialis JS17 amine transaminase

Comparison of Four Immobilization Methods for Different Transaminases

Biocatalytic syntheses often require unfavorable conditions, which can adversely affect enzyme stability. Consequently, improving the stability of biocatalysts is needed, and this is often achieved by immobilization. In this study, we aimed to compare the stability of soluble and immobilized transaminases from different species. A cysteine in a consensus sequence was converted to a single aldehyde by the formylglycine-generating enzyme for directed single-point attachment to amine beads. This immobilization was compared to cross-linked enzyme aggregates (CLEAs) and multipoint attachments to glutaraldehyde-functionalized amine- and epoxy-beads. Subsequently, the reactivity and stability (i.e., thermal, storage, and solvent stability) of all soluble and immobilized transaminases were analyzed and compared under different conditions. The effect of immobilization was highly dependent on the type of enzyme, the immobilization strategy, and the application itself, with no superior immobilization technique identified. Immobilization of HAGA-beads often resulted in the highest activities of up to 62 U/g beads, and amine beads were best for the hexameric transaminase from Luminiphilus syltensis. Furthermore, the immobilization of transaminases enabled its reusability for at least 10 cycles, while maintaining full or high activity. Upscaled kinetic resolutions (partially performed in a SpinChemTM reactor) resulted in a high conversion, maintained enantioselectivity, and high product yields, demonstrating their applicability.

Recombinant L-Amino Acid Oxidase with broad substrate spectrum for Co-Substrate Recycling in (S)-Selective Transaminase-Catalyzed Kinetic Resolutions

Chiral and enantiopure amines can be produced by enantioselective transaminases via kinetic resolution of amine racemates. This transamination reaction requires stoichiometric amounts of co-substrate. A dual-enzyme recycling system overcomes this limitation: L-amino acid oxidases (LAAO) recycle the accumulating co-product of ( S )-selective transaminases in the kinetic resolution of racemic amines to produce pure ( R )-amines. However, availability of suitable LAAOs is limited. Here we use the heterologously produced, highly active fungal hcLAAO4 with broad substrate spectrum. H 2 O 2 as by-product of hcLAAO4 is detoxified by a catalase. The final system allows using sub-stoichiometric amounts of 1 mol% of the transaminase co-substrate as well as the initial application of L-amino acids instead of α-keto acids. With an optimized protocol, synthetic potential of this kinetic resolution cascade was proven at the preparative scale (>90 mg) by the synthesis of highly enantiomerically pure ( R )-methylbenzylamine (>99 %ee) at complete conversion (50 %).

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.

The Effect of Visible Light on the Catalytic Activity of PLP-Dependent Enzymes

Pyridoxal 5'-phosphate (PLP)-dependent enzymes are a versatile class of biocatalysts and feature a variety of industrial applications. However, PLP is light sensitive and can cause inactivation of enzymes in certain light conditions. As most of the PLP-dependent enzymes are usually not handled in dark conditions, we evaluated the effect of visible light on the activity of PLP-dependent enzymes during production as well as transformation. We tested four amine transaminases, from Chromobacterium violaceum, Bacillus megaterium, Vibrio fluvialis and a variant from Arthrobacter species as well as two lysine decarboxylases, from Selenomonas ruminantium and the LDCc from Escherichia coli. It appeared that five of these six enzymes suffered from a significant decrease in activity by up to 90 % when handled in laboratory light conditions. Surprisingly, only the amine transaminase variant from Arthrobacter species appeared to be unaffected by light exposure and even showed an activation to 150 % relative activity over the course of 6 h regardless of the light conditions.

ω-Transaminase-Mediated Asymmetric Synthesis of (S)-1-(4-Trifluoromethylphenyl)Ethylamine

The pivotal role played by ω-transaminases (ω-TAs) in the synthesis of chiral amines used as building blocks for drugs and pharmaceuticals is widely recognized. However, chiral bulky amines are challenging to produce. Herein, a ω-TA (TR8) from a marine bacterium was used to synthesize a fluorine chiral amine from a bulky ketone. An analysis of the reaction conditions for process development showed that isopropylamine concentrations above 75 mM had an inhibitory effect on the enzyme. Five different organic solvents were investigated as co-solvents for the ketone (the amine acceptor), among which 25–30% (v/v) dimethyl sulfoxide (DMSO) produced the highest enzyme activity. The reaction reached equilibrium after 18 h at 30% of conversion. An in situ product removal (ISPR) approach using an aqueous organic two-phase system was tested to mitigate product inhibition. However, the enzyme activity initially decreased because the ketone substrate preferentially partitioned into the organic phase, n-hexadecane. Consequently, DMSO was added to the system to increase substrate mass transfer without affecting the ability of the organic phase to prevent inhibition of the enzyme activity by the product. Thus, the enzyme reaction was maintained, and the product amount was increased for a 62 h reaction time. The investigated ω-TA can be used in the bioconversion of bulky ketones to chiral amines for future bioprocess applications.

Stabilization of ω-transaminase from Pseudomonas fluorescens by immobilization techniques

Transaminases are a class of enzymes with promising applications for the preparation and resolution of a vast diversity of valued amines. Their poor operational stability has fueled many investigations on its stabilization due to their biotechnological relevance. In this work, we screened the stabilization of the tetrameric ω-transaminase from Pseudomonas fluorescens (PfωTA) through both carrier-bound and carrier-free immobilization techniques. The best heterogeneous biocatalyst was the PfωTA immobilized as cross-linked enzyme aggregates (PfωTA-CLEA) which resulted after studying different parameters as the precipitant, additives and glutaraldehyde concentrations. The best conditions for maximum recovered activity (29 %) and maximum thermostability at 60 ºC and 70 ºC (100 % and 71 % residual activity after 1 h, respectively) were achieved by enzyme precipitation with 90% acetone or ethanol, in presence of BSA (100 mg/mL) and employing glutaraldehyde (100 mM) as cross-linker. Studies on different conditions for PfωTA-CLEA preparation yielded a biocatalyst that exhibited 31 and 4.6 times enhanced thermal stability at 60 °C and 70 °C, respectively, compared to its soluble counterpart. The PfωTA-CLEA was successfully used in the bioamination of 4-hydroxybenzaldehyde to 4-hydroxybenzylamine. To the best of our knowledge, this is the first report describing a transaminase cross-linked enzyme aggregates as immobilization strategy to generate a biocatalyst with outstanding thermostability.

Enhancing PLP-Binding Capacity of Class-III ω-Transaminase by Single Residue Substitution

Transaminases are pyridoxal-5′-phosphate (PLP) binding enzymes, broadly studied for their potential industrial application. Their affinity for PLP has been related to their performance and operational stability and while significant differences in PLP requirements have been reported, the environment of the PLP-binding pocket is highly conserved. In this study, thorough analysis of the residue interaction network of three homologous transaminases Halomonas elongata (HeTA), Chromobacterium violaceum (CvTA), and Pseudomonas fluorescens (PfTA) revealed a single residue difference in their PLP binding pocket: an asparagine at position 120 in HeTA. N120 is suitably positioned to interact with an aspartic acid known to protonate the PLP pyridinium nitrogen, while the equivalent position is occupied by a valine in the other two enzymes. Three different mutants were constructed (HeTA-N120V, CvTA-V124N, and PfTA-V129N) and functionally analyzed. Notably, in HeTA and CvTA, the asparagine variants, consistently exhibited a higher thermal stability and a significant decrease in the dissociation constant (K_d) for PLP, confirming the important role of N120 in PLP binding. Moreover, the reaction intermediate pyridoxamine-5′-phosphate (PMP) was released more slowly into the bulk, indicating that the mutation also enhances their PMP binding capacity. The crystal structure of PfTA, elucidated in this work, revealed a tetrameric arrangement with the PLP binding sites near the subunit interface. In this case, the V129N mutation had a negligible effect on PLP-binding, but it reduced its temperature stability possibly destabilizing the quaternary structure.