Biochemical and Thermodynamic Studies on a Novel Thermotolerant GH10 Xylanase from Bacillus safensis .

Xylanases have a broad range of applications in agro-industrial processes. In this study, we report on the discovery and characterization of a new thermotolerant GH10 xylanase from Bacillus safensis , designated as BsXyn10. The xylanase gene ( bsxyn10 ) was cloned from Bacillus safensis and expressed in Escherichia coli . The reduced molecular mass of BsXyn10 was 48 kDa upon SDS-PAGE. Bsxyn10 was optimally active at pH 7.0 and 60 °C, stable over a broad range of pH (5.0-8.0), and also revealed tolerance toward different modulators (metal cations, EDTA). The enzyme was active toward various xylans with no activity on the glucose-based polysaccharides. K M , v max , and k cat for oat spelt xylan hydrolysis were found to be 1.96 g·L -1 , 58.6 μmole·min -1 ·(mg protein) -1 , and 49 s -1 , respectively. Thermodynamic parameters for oat spelt xylan hydrolysis at 60 °C were ΔS* = -61.9 J·mol -1 ·K -1 , ΔH* = 37.0 kJ·mol -1 and ΔG* = 57.6 kJ·mol -1 . BsXyn10 retained high levels of activity at temperatures up to 60 °C. The thermodynamic parameters (ΔH* D , ΔG* D , ΔS* D ) for the thermal deactivation of BsXyn10 at a temperature range of 40-80 °C were: 192.5 ≤ ΔH* D ≤ 192.8 kJ·mol -1 , 262.1 ≤ ΔS* D ≤ 265.8 J·mol -1 ·K -1 , and 99.9 ≤ ΔG* D ≤ 109.6 kJ·mol -1 . The BsXyn10-treated oat spelt xylan manifested the catalytic release of xylooligosaccharides of 2-6 DP, suggesting that BsXyn10 represents a promising candidate biocatalyst appropriate for several biotechnological applications.