A thermostable leucine dehydrogenase from Bacillus coagulansNL01: Expression, purification and characterization

L-Tert-leucine is the most representative unnatural amino acid and its production is valuable in industry. At present, l-tert-leucine is mainly produced by bioconversion, in which leucine dehydrogenase (LeuDH) plays a major role. In this study, a highly thermo- and pH-stable LeuDH from Bacillus coagulans NL01 (Bc-LeuDH) was reported and successfully expressed in Escherichia coli BL21(DE3). The enzyme was purified and its enzymatic properties were characterized. The specific activity of Bc-LeuDH at optimum condition (pH 8.0 and 50 °C) is 1337.97 U/mg, and the Km and kcat for sodium α-ketoisocaproate was 1.369 mM and 0.125 S-1, respectively. Furthermore, Bc-LeuDH possessed excellent thermostability that held nearly 80 % activity after 72 h incubation at temperature 50 °C and 55 °C. Notably, the half-life of Bc-LeuDH activity also was long for near 12 h at a high temperature of 70 °C, which was the longest in previous reports. Based on the sequence and structure analysis, the hydrophobic amino acid residues and hydrophobic patches are considered to have an important contribution to the thermostability of Bc-LeuDH. Furthermore, the Bc-LeuDH demonstrated better pH stability over a wide pH ranging from 7.0-10.0. These results indicate the potential industrial application of Bc-LeuDH in the future.