Xylanase and Acetyl Xylan Esterase Activities of XynA, a Key Subunit of the Clostridium cellulovorans Cellulosome for Xylan Degradation

The Clostridium cellulovorans xynA gene encodes the cellulosomal endo-1,4-β-xylanase XynA, which consists of a family 11 glycoside hydrolase catalytic domain (CD), a dockerin domain, and a NodB domain. The recombinant acetyl xylan esterase (rNodB) encoded by the NodB domain exhibited broad substrate specificity and released acetate not only from acetylated xylan but also from other acetylated substrates. rNodB acted synergistically with the xylanase CD of XynA for hydrolysis of acetylated xylan. Immunological analyses revealed that XynA corresponds to a major xylanase in the cellulosomal fraction. These results indicate that XynA is a key enzymatic subunit for xylan degradation in C. cellulovorans.