Expression of A. niger US368 xylanase in E. coli: Purification, characterization and copper activation

The XAn11 cDNA was cloned in pET-28a(+) and the recombinant plasmid was transformed in Escherichia coli. The His-tagged r-XAn11 was purified using Ni-NTA affinity and anion exchange chromatography. The enzyme showed a specific activity of 415.1 U mg−1 and a molecular mass of 25 kDa. It had an optimal activity at pH 5 and 50 °C. It was stable in a wide range of pH and in the presence of some detergents and organic solvents. In the presence of 3 mM Cu2+, the relative activity of the His-tagged r-XAn11 was enhanced by 54%. This is the first work reporting that copper is a strong activator for xylanase activity making this enzyme very attractive for future industrial applications. Molecular modeling suggests that the contact region between the catalytic site and the N-terminal His-tag fusion peptide could be responsible for the different behavior of the native and recombinant enzyme toward copper.