Summary of enzymatic activities
Xylans are plant cell wall components and potentially impede digestion of walls by cellulases. Xylanases are extracellular enzymes which allow organisms to use xylans as carbon sources. They've been isolated from a wide range of organisms.
In general xylanases are thermotolerent and have broad pH optima. They generally have two glutamic acids at the active site, a hydrogen ion donor and a hydrogen ion acceptor. Glutamic acid's ability to donate hydrogen ions diminishes at high pH. Alkaline xylanases mitigate this limitation by raising the pKa (through mutations) of one of the glutamic acids, extending the alkaline limb of the pH activity curve as illustated in the following figure.
Xylanase, alkaline xylanase and recombinants