Nucleotide sequence of the Clostridium stercorarium xylA gene encoding a bifunctional protein with beta-D-xylosidase and alpha-L-arabinofuranosidase activities, and properties of the translated product

Abstract

The nucleotides of the beta-xylosidase (xylA) gene from Clostridium stercorarium were sequenced. A single open reading frame of 473 codons specifying the subunit (MW 53,340) of xylosidase was identified. The N-terminal amino acid sequence and molecular weight estimated by SDS-polyacrylamide gel electrophoresis of the purified enzyme were quite in agreement with those deduced from the nucleotide sequence. Analysis of the enzyme by gel filtration on an HPLC column gave a molecular weight of 220,000, suggesting that the native enzyme is a tetramer composed of 4 identical subunits. The pH optimum was 7.0 and quite stable over the pH range of 5 to 10 at 4 degrees C. The optimum temperature was 65 degrees C. Vm was estimated to be 5.9 nmol/min/micrograms for p-nitrophenyl-beta-D-xylopyranoside and 16.7 nmol/min/micrograms for p-nitrophenyl-alpha-L-arabinofuranoside, while Km was estimated to be 2.5 mM for p-nitrophenyl-beta-D-xylopyranoside and 17.6 mM for p-nitrophenyl-alpha-L-arabinofuranoside.