Enzymatic specificity and hydrolysis pattern of the catalytic domain of the xylanase Xynl from Rhodothermus marinus.

The catalytic domain of a xylanase from Rhodothermus marinus was produced in Escherichia coli. The catalytic domain belongs to glycosyl hydrolase family 10. The produced protein has a 22-amino acid leader peptide followed by a 411-amino acid truncated xylanase. The molecular mass was 48 kDa and the recombinant xylanase had a pI of 4.9. The pH and temperature optima for activity were determined to be 7.5 and 80 degrees C, respectively. At that temperature the enzyme had a half-life of 1 h 40 min. An addition of 1 mM calcium stabilized the activity of the enzyme at 80 degrees C. The xylanase had its highest specific activity on oat spelt xylan but was active also on other xylans and to a limited extent on some other polysaccharides (soluble glucans). No exo- or endo-cellulase activity was observed. Hydrolysis of xylo-oligomers and oat spelt xylan was studied and the predominant products of hydrolysis were xylobiose and xylotriose. The enzyme was inactive on xylobiose, xylotriose and on the soluble fraction from oat spelt xylan. The R. marinus xylanase is shown to have a strong preference for internal linkages and is therefore classified as an endo-xylanase.