Thermostable xylanase10B from <Emphasis Type="Italic">Clostridium acetobutylicum</Emphasis> ATCC824

The Clostridium acetobutylicum xylanase gene xyn10B (CAP0116) was cloned from the type strain ATCC 824, whose genome was recently sequenced. The nucleotide sequence of C. acetobutylicum xyn10B encodes a 318-amino acid protein. Xyn10B consists of a single catalytic domain that belongs to family 10 of glycosyl hydrolases. The enzyme was purified from recombinant Escherichia coli. The Xyn10B enzyme was highly active toward birchwood xylan, oat-spelt xylan, and moderately active toward avicel, carboxymethyl cellulose, polygalacturonic acid, lichenan, laminarin, barley--glucan and various p-nitrophenyl monosaccharides. Xyn10B hydrolyzed xylan and xylooligosaccharides to produce xylobiose and xylotriose. The pH optimum of Xyn10B was 5.0, and the optimal temperature was 70°C. The enzyme was stable at 60°C at pH 5.0–6.5 for 1 h without substrate. This is one of a number of xylan-related activities encoded on the large plasmid in C. acetobutylicum ATCC 824.