Abstract
The Clostridium stercorarium F-9 xyl43B gene encoding the β-xylosidase Xyl43B consists of an open reading frame of 1,491 nucleotides that encodes a putative protein, classified in family 43, of 497 amino acids with a predicted molecular weight of 56,355. The deduced amino acid sequence of Xyl43B has sequence similarity with β-xylosidases from Bacteriodes thetaiotaomicron (57% sequence identity), Prevotella ruminicola (45%), Streptomyces coelicolor (40%), and Clostridium acetobutylicum (36%), all of which have been classified in family 43 of the glycoside hydrolases. Xyl43B was purified from a recombinant Escherichia coli and characterized. The optimum pH of the purified enzyme was 3.5 and it was stable over pH from 3.0 to 8.0. Its optimum temperature was 80°C and it showed thermostability in the temperature range from 50 to 70°C. Xyl43B had a Km of 6.2 mM and a Vmax of 15 μmol min−1 mg−1 for p-nitrophenyl-β-D-xylopyranoside.
