Cellulose Binding Domains and Linker Sequences Potentiate the Activity of Hemicellulases Against Complex Substrates

To evaluate the role of the CBDs and linker sequences in Pseudomonas xylanase A (XYLA) and arabinofuranosidase C (XYLC), the catalytic activity of derivatives of these enzymes, lacking either the linker sequences or CBDs, was assessed. Removal of the CBDs or linker sequences did not affect the activity of either XYLA or XYLC against soluble arabinoxylan, while derivatives of XYLA, in which either the CBD or interdomain regions had been deleted, exhibited decreased activity against the xylan component of cellulose/hemicellulose complexes. Although a truncated derivative of XYLC (XYLC"'), lacking its CBD, was less active than the full-length enzyme against plant cell wall material containing highly substituted arabinoxylan, XYLC"' was more active than XYLC on complex substrates where the degree of substitution of arabinoxylan was very low. These data indicate that CBDs and linker sequences play an important role in the activity of hemicellulases against plant cell walls and other cellulose/hemicellulose complexes.