Gene Cloning and Characterization of an Acidic Xylanase from Acidobacteriu

The gene xynA encoding an acid endo-β-1,4-xylanase from an acidophilic bacterium, Acidobacterium capsulatum 161, was cloned and expressed in Escherichia coli. The nucleotide sequence of the 1.6-kb DNA fragment containing xynA was analyzed, revealing an open reading frame of 1,215 bp encoding a peptide of 405 amino acid residues. The deduced amino acid sequence of XynA was very similar to other xylanases that are from the glycosyl hydrolase family 10. XynA was purified to homogeneity by SDS-polyacrylamide gel electrophoresis from E. coli transformants. The molecular mass and isoelectric point of XynA were 41 kDa and 7.3, respectively. The xylanase activity of the cloned XynA is an endo-acting enzyme that shows optimal activity at pH 5.0 and 65°C, and is stable pH between 3.0 and 8.0. The K_m and V_max with oat spelt xylan as a substrate at pH 5.0 and 30°C are 3.5 mg/ml and 403 μmol/min/mg.