Secretory expression and characterization of a novel amidase from Kluyvera cryocrescens in Bacillus subtilis

Objective: Cloning and secretory expression of an amidase from Kluyvera cryocrescens and characterization of its potential in preparation of chiral amino acids. Results: An amidase belonging to the Ntn-hydrolase superfamily was identified from Kluyvera cryocrescens ZJB-17005 (Kc-Ami). The maximum activity of Kc-Ami was observed at pH 8.5 and 55 °C. Remarkably, Kc-Ami showed an excellent enantioselectivity (99% ee) using rac-4-(hydroxy(methyl)phosphoryl)-2-(2-phenylacetamido) butanoic acid as substrate. Kc-Ami remained stable at pH 7.0–9.0 and exhibited prominent thermostability with a half-life time of 59.1, 47.4 and 20.4 h at 50, 55 and 60 °C, respectively. Kc-Ami could be appllied to synthesize chiral amino acids and its derivatives with excellent enantioselectivity (> 99% ee). The synthesized chiral amino acids could contain short or long side chain, and further the side chain could be replaced with –OH, –COOH or benzene ring. Conclusions: Kc-Ami exhibited remarkable thermostability and excellent enantioselectivity for synthesizing chiral amino acids and its derivatives. This specific characteristic provides great potential for industrial application in preparation of chiral amino acids and its derivatives.