High-Throughput Screening Method for Directed Evolution and Characterization of Aldol Activity of D-Threonine Aldolase.

A rapid and reliable method for the determination of aldol condensation activity of threonine aldolases (TAs) toward aldehydes and glycine was developed. This 2,4-dinitrophenylhydrazine (DNPH) method has high sensitivity and low background disturbance and can be spectrophotometrically measured for high-throughput screening and characterization of TAs. For 4-methylsulfonyl benzaldehyde (MSB), the maximum absorbance peak was observed at around 485 nm. Site-directed saturation mutagenesis libraries of D-threonine aldolase from Alcaligenes xylosoxidans CGMCC 1.4257 (AxDTA) was constructed and screened with this DNPH method for increased aldol activity toward MSB. Two beneficial variants AxDTAD321C and AxDTAN101G were identified. Substrate specificity of AxDTA and variants toward nineteen aldehydes with different substituents was facilely characterized employing this DNPH method. Furthermore, AxDTA variants displayed enhanced catalytic performance and selectivity in aldol reaction. Consequently, our study provides a rapid screening and characterization method for TAs with potential applications in preparation of chiral β-hydroxy-α-amino acids.