Characterization of a xylanase belonging to the glycoside hydrolase family 5 subfamily 35 from Paenibacillus sp. H2C

Corn xylan is resistant to enzymatic hydrolysis due to its complex structure. We characterized PsXyn5A, an enzyme highly active for corn xylan, isolated from Paenibacillus sp. H2C. PsXyn5A is a modular xylanase with a catalytic domain belonging to the glycoside hydrolase family 5 subfamily 35 (GH5_35) and a carbohydrate-binding module family 13 (CBM13) domain. The substrate recognition mechanism of GH5_35 xylanase has not been reported. Analysis of the hydrolysate from rye arabinoxylan (RAX) has shown that the GH5_35 catalytic domain of PsXyn5A recognizes an arabinofuranosyl (Araf) side residue and cleaves the reducing terminal side of Araf-linked xylopyranose. This cleavage specificity is the same as reported for the GH5_34 xylanase from Hungateiclostridium thermocellum (HtXyl5A). Unlike HtXyl5A, PsXyn5A produced Araf-xylopyranose from RAX and did not hydrolyze 3(3)-alpha-l-Araf-xylotetraose. Deletion of the CBM13 domain significantly decreased the activity toward insoluble corn xylan, indicating that CBM13 plays an essential role in hydrolyzing corn xylan.