Cloning, expression, and characterization of a thermostable and pH-stable laccase from Klebsiella pneumoniae and its application to dye decolorization

A thermostable and pH-stable laccase from Klebsiella pneumoniae was cloned and expressed in Escherichia coli. The recombinant laccase (rLac) achieved a specific activity of 7.12 U/mg after purification by Ni-affinity chromatography. Optimal enzyme activity was observed at pH 4.0 and 35 degrees C for 2,2'-azino-bis (3-ethylbenzthiazoline sulfonic acid) (ABTS) oxidization and pH 8.0 and 70 degrees C for 2,6dimethoxyphenol (2,6-DMP) oxidization. Thermostability and pH stability studies showed that the rLac was stable over the range of 30-70 degrees C and pH 5.0-9.0 using 2,6-DMP as substrate. Circular dichroism analysis suggested that the secondary structure of the rLac mainly consisted of a-helix that played a vital role in maintaining laccase activity and revealed the potential mechanisms for the changes in laccase activity under varying pHs (3.0-11.0) and temperatures (20-90 degrees C). Finally, the rLac could decolorize the tested dyes with high decolorization efficiency. (C) 2016 Elsevier Ltd. All rights reserved.