Applicability of recombinant β-xylosidase from the extremely thermophilic bacterium Geobacillus thermodenitrificans in synthesizing alkylxylosides.

Abstract The β-xylosidase encoding gene ( XsidB ) of the extremely thermophilic bacterium Geobacillus thermodenitrificans has been cloned and expressed in Escherichia coli. The homotrimeric recombinant XsidB is of 204.0 kDa, which is optimally active at 60 °C and pH 7.0 with T 1/2 of 58 min at 70 °C. The β-xylosidase remains unaffected in the presence of most metal ions and organic solvents. The K m [p-nitrophenyl β-xyloside (pNPX)], V max and k cat values of the enzyme are 2 × 10 −3  M, 1250 μmoles mg −1  min −1 and 13.20 × 10 5  min −1 , respectively. The enzyme catalyzes transxylosylation reactions in the presence of alcohols as acceptors. The pharmaceutically important β-methyl- d -xylosides could be produced using pNPX as the donor and methanol as acceptor. The products of transxylosylation were identified by TLC and HPLC, and the structure was confirmed by 1 H NMR analysis. The enzyme is also useful in synthesizing transxylosylation products from the wheat bran hydrolysate.