An efficient colorimetric high-throughput screening method for synthetic activity of tyrosine phenol-lyase

High-throughput assay of tyrosine phenol-lyase activity using a cascade of enzymatic reactions

Tyrosine phenol-lyase (TPL) exhibits great potential in industrial biosynthesis of l-tyrosine and its derivates. To uncover and screen TPLs with excellent catalytic properties, there is unmet demand for development of facile and reliable screening system for TPL. Here we presented a novel assay format for the detection of TPL activity based on catechol 2,3-dioxygenase (C23O)-catalyzed reaction. Catechol released from TPL-catalyzed cleavage of 3,4-dihydroxy-l-phenylalanine (l-DOPA) was further oxidized by C23O to form 2-hydroxymuconate semialdehyde, which could be readily detected by spectrophotometric measurements at 375 nm. The assay achieved a unique balance between the ease of operation and superiority of analytical performances including linearity, sensitivity and accuracy. In addition, this assay enabled real-time monitoring of TPL activity with high efficiency and reliability. As C23O is highly specific towards catechol, a non-natural product of microorganism, the assay was therefore accessible to both crude cell extracts and the whole-cell system without elaborate purification steps of enzymes, which could greatly expedite discovery and engineering of TPLs. This study provided fundamental principle for high-throughput screening of other enzymes consuming or producing catechol derivatives.

Winning the numbers game in enzyme evolution - fast screening methods for improved biotechnology proteins

The booming demand for environmentally benign industrial processes relies on the ability to quickly find or engineer a biocatalyst suitable to ideal process conditions. Both metagenomic approaches and directed evolution involve the screening of huge libraries of protein variants, which can only be managed reasonably by flexible platforms for (ultra)high-throughput profiling against the desired criteria. Here, we review the most recent additions toward a growing toolbox of versatile assays using fluorescence, absorbance and mass spectrometry readouts. While conventional solution based high-throughput screening in microtiter plate formats is still important, the implementation of novel screening protocols for microfluidic cell or droplet sorting systems supports technological advances for ultra-high-frequency screening that now can dramatically reduce the timescale of engineering projects. We discuss practical issues of scope, scalability, sensitivity and stereoselectivity for the improvement of biotechnologically relevant enzymes from different classes.

Integrating enzyme evolution and high-throughput screening for efficient biosynthesis of l-DOPA

l-DOPA is a key pharmaceutical agent for treating Parkinson’s, and market demand has exploded due to the aging population. There are several challenges associated with the chemical synthesis of l-DOPA, including complicated operation, harsh conditions, and serious pollution. A biocatalysis route for l-DOPA production is promising, especially via a route catalyzed by tyrosine phenol lyase (TPL). In this study, using TPL derived from Erwinia herbicola (Eh-TPL), a mutant Eh-TPL was obtained by integrating enzyme evolution and high-throughput screening methods. l-DOPA production using recombinant Escherichia coli BL21 (DE3) cells harbouring mutant Eh-TPL was enhanced by 36.5% in shake flasks, and the temperature range and alkali resistance of the Eh-TPL mutant were promoted. Sequence analysis revealed two mutated amino acids in the mutant (S20C and N161S), which reduced the length of a hydrogen bond and generated new hydrogen bonds. Using a fed-batch mode for whole-cell catalysis in a 5 L bioreactor, the titre of l-DOPA reached 69.1 g L−1 with high productivity of 11.52 g L−1 h−1, demonstrating the great potential of Eh-TPL variants for industrial production of l-DOPA.

Efficient biocatalyst of L-DOPA with Escherichia coli expressing a tyrosine phenol-lyase mutant from Kluyvera intermedia

L-DOPA (L-dihydroxyphenylalanine) is a promising drug for Parkinson's disease and thereby has a growing annual demand. Tyrosine phenol-lyase (TPL)-based catalysis is considered to be a low-cost yet efficient route for biosynthesis of L-DOPA. TPL is a tetrameric enzyme that catalyzes the synthesis of L-DOPA from pyrocatechol, sodium pyruvate, and ammonium acetate. The implementation of TPL for L-DOPA production has been hampered and the need for the most efficient TPL source with higher L-DOPA production and substrate conversion rate is prevailing. This study involves identifying a novel TPL from Kluyvera intermedia (Ki-TPL) and displayed a robust expression in Escherichia coli. The recombinant strain YW000 carrying Ki-TPL proved strong catalytic activity with a highest L-DOPA yield compared with 16 other TPLs from different organisms. With a further aim to improve this efficiency, random mutagenesis of Ki-TPL was performed and a mutant namely YW021 was obtained. The whole cells of YW021 as biocatalyst yielded 150.4 g L^-1 of L-DOPA with a 99.99 % of pyrocatechol conversion at the optimum condition of pH 8.0 at 25 °C, which is the highest level reported to date. Further, the homology modeling and structural analysis revealed the mutant residues responsible for the extensive L-DOPA biosynthesis.

Efficient separation of α-ketoglutarate from Yarrowia lipolytica WSH-Z06 culture broth by converting pyruvate to l-tyrosine

Co-production of α-ketoglutaric acid (KGA) and pyruvic acid (PYR) by Yarrowia lipolytica WSH-Z06 could significantly increase the final titer and yield of keto acids. However, efficient separation of KGA and PYR in an economic manner is a big challenge owing to their similar properties. In the present study, a separation process was established to convert PYR in the fermentation broth to l-tyrosine (TYR). Owing to its low solubility, TYR was easily precipitated out and could be easily removed from the reaction system. The whole-cell catalysis reaction solution was subjected to acid treatment, centrifugation, cation exchange column separation, rotary evaporation, Buchner funnel filtration, and dry separation method to obtain KGA and TYR powders. The purity/recovery rates of KGA and TYR were 98.16%/78.68% and 98.19%/73.46%, respectively. The use of biological pathways to separate KGA from the culture broth could make the separation process easier and further decrease the operation cost.

A high-throughput screening method for improved R-2-(4-hydroxyphenoxy)propionic acid biosynthesis

R-2-(4-hydroxyphenoxy)propionic acid (R-HPPA) is a key intermediate of the enantiomerically pure phenoxypropionic acid herbicides. R-HPPA could be biosynthesized through selective introduction of a hydroxyl group (-OH) into the substrate R-2-phenoxypropionic acid (R-PPA) at C-4 position, facilitated by microorganisms with hydroxylases. In this study, an efficient high-throughput screening method for improved R-HPPA biosynthesis through microbial hydroxylation was developed. As a hydroxylated aromatic product, R-HPPA could be oxidized by oxidant potassium dichromate to form brown-colored quinone-type compound. The concentration of R-HPPA can be quantified according to the absorbance of the colored compound at a suitable wavelength of 570 nm; and the R-HPPA biosynthetic capability of microorganism strains could also be rapidly evaluated. After optimization of the assay conditions, the high-throughput screening method was successfully used in identification of Beauveria bassiana mutants with enhanced R-HPPA biosynthesis capacity. A positive mutant C-7 with high tolerance to 20 g/L R-PPA was rapidly selected from 1920 mutants. The biomass and R-HPPA titer were 12.5- and 38.19-fold higher compared with the original strain at 20 g/L R-PPA. This high-throughput screening method developed in this work could also be a potential tool for screening strains producing other important phenolic compounds.

A novel anti Candida albicans drug screening system based on high-throughput microfluidic chips

Due to the antibacterial resistance crisis, developing new antibacterials is of particular interest. In this study, we combined the antifungal drug amphotericin B with 50,520 different small molecule compounds obtained from the Chinese National Compound Library in an attempt to improve its efficacy against Candida albicans persister cells. To systematically study the antifungal effect of each compound, we utilized custom-designed high-throughput microfluidic chips. Our microfluidic chips contained microchannels ranging from 3 µm to 5 µm in width to allow Candida albicans cells to line up one-by-one to facilitate fluorescence-microscope viewing. After screening, we were left with 10 small molecule compounds that improved the antifungal effects of amphotericin B more than 30% against Candida albicans persister cells.