Microbial production of ketoreductases: Development of a novel high-throughput screening method

Novel Detection Method for Evaluating the Activity of an Alkaline Serine Protease from Bacillus clausii

Until now, the detection methods for serine proteases have been quite time-consuming or cannot indicate the "real" protease activity. Here, a rapid and simple method for determining the "real" activity of serine proteases toward AAPX (a kind of mixed polypeptide substrates, with X representing 20 standard amino acids) was developed. This AAPX method has high reliability, sensitivity, and repeatability and can be used for detecting the serine protease activity spectrophotometrically. Additionally, the site-directed saturation mutagenesis library of alkaline serine protease PRO (BcPRO) from Bacillus clausii was screened with this AAPX method. Three beneficial mutants S99R, S99H, and S99W were identified, and S99W displayed the highest activity. In comparison to wild-type BcPRO, S99W exhibited enhanced catalytic performance toward eight AAPX monomers, and the molecular dynamics simulation revealed the mechanism responsible for its improved activity toward AAPM. Consequently, this work provides an efficient method for detecting, characterizing, mining, and high-throughput screening of serine proteases.

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.

Screening of Fungi Isolates for C-4 Hydroxylation of R-2-Phenoxypropionic Acid Based on a Novel 96-Well Microplate Assay Method

R-2-(4-Hydroxyphenoxy)propionic acid (R-HPPA) is a pivotal intermediate for the synthesis of aryloxyphenoxypropionate (APP) herbicide. To rapidly screen microbial isolates with the capacity of hydroxylating R-2-phenoxypropionic acid to R-HPPA from various environmental samples, a convenient and safe 96-well microplate assay method with sodium nitrite (NaNO₂) as chromogenic reagent was proposed and optimized. The optimum assay conditions were as follows: the detection wavelength was 420 nm, the concentration of NaNO₂ solution was 6.0 g/L, color reaction temperature was 60 °C, the pH of the NaNO₂ solution was 2.4, and the reaction time was 40 min. With the aid of this method, screening for microorganisms with C-4-specific hydroxylation activity of R-PPA was conducted. As a result, 23 strains among 3744 single colonies isolated from various samples exhibited the hydroxylation activity. Among these strains, the highest bioconversion rate was achieved by Penicillium oxalicum A5 and Aspergillus versicolor A12, respectively. After 72-h cultivation in shake flask, their conversion rates of R-HPPA from 10 g/L R-PPA reached 21.18% and 40.24%, respectively. The established method was effective in rapid screening of microbes capable of biosynthesizing R-HPPA through hydroxylation of R-PPA, and the obtained two fungi species could be potentially used for R-HPPA production.