Characterization of a highly thermostable glycoside hydrolase family 10 xylanase from Malbranchea cinnamomea.

A thermostable xylanase (McXyn10) from the thermophilic fungus Malbranchea cinnamomea strain S168 was purified and biochemically characterized. The enzyme was purified to homogeneity with a molecular mass of 43.5 kDa on SDS-PAGE. The optimal pH and temperature of the purified enzyme were pH 6.5 and 80°C, respectively. The enzyme showed a broad range of pH stability (pH 4.0-10.5), and was stable up to 70°C with a thermal denaturing half life of 76.0 min. The enzyme exhibited strict specificity for various xylans as substrates, but displayed no activity toward other tested polysaccharides. McXyn10 hydrolyzed birchwood xylan, beechwood xylan and oat-spelt xylan, yielded mainly xylobiose, xylotriose and xylooligosaccharides with degree of polymerization (DP) above 5, while yielded xylobiose from xylotriose and xylotetraose. The xylanase gene was further cloned. It had an open reading frame of 1191 bp with two introns. The deduced amino acid sequence of the gene showed highest identity (58%) with a glycoside hydrolase family 10 xylanase from Aureobasidium pullulans.