Endoxylanase that degrades arabinoxylan and glucuronoxylan to xylobiose and xylotriose (in vitro). Endohydrolysis of (1->4)-beta-D-xylosidic linkages in xylans. Optimum pH is 6.5-7.0. Optimum temperature is 75 degrees Celsius. Thermostable. Glycan degradation; xylan degradation. Up-regulated by growth on xylan. XynA is a modular enzyme. The number of CBM6 (carbohydrate binding type-6) domains varies between strains. The polymeric substrate can interact with several of these CBM6 domains. Belongs to the glycosyl hydrolase 11 (cellulase G) family.