Cloning, purification and characterization of a cellulase-free xylanase from Geobacillus thermodenitrificans AK53

Abstract

Geobacillus thermodenitrificans AK53 xyl gene encoding xylanase was isolated, cloned and expressed in Escherichia coli. After purifying recombinant xylanase from G. thermodenitrificans AK53 (GthAK53Xyl) to homogeneity by ammonium sulfate precipitation and ion exchange chromatography, biochemical properties of the enzyme were determined. The kinetic studies for GthAK53Xyl showed K_M value to be 4.34 mg/mL (for D-xylose) and V_max value to be 2028.9 μmoles mg^–1 min^–1. The optimal temperature and pH for enzyme activity were found out to be 70°C and 5.0, respectively. The expressed protein showed the highest sequence similarity with the xylanases of G. thermodenitrificans JK1 (JN209933) and G. thermodenitrificans T-2 (EU599644). Metal cations Mg²⁺ and Mn²⁺ were found to be required for the enzyme activity, however, Co²⁺, Hg²⁺, Fe²⁺ and Cu²⁺ ions caused inhibitor effect on it. GthAK53Xyl had no cellulolytic activity and degraded xylan in an endo-fashion. The action of the enzyme on xylan from oat spelt produced xylobiose and xylopentose. The reported results are suggestive of a xylanase exhibiting desirable kinetics, stability parameters and metal resistance required for the efficient production of xylobiose at industrial scale.