The biological conversion of cellulose to glucose generally requires three types of hydrolytic enzymes: (1) Endoglucanases which cut internal beta-1,4-glucosidic bonds; (2) Exocellobiohydrolases that cut the disaccharide cellobiose from the non-reducing end of the cellulose polymer chain; (3) Beta-1,4-glucosidases which hydrolyze the cellobiose and other short cello-oligosaccharides to glucose. Hydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose and cellotetraose, releasing cellobiose from the non-reducing ends of the chains. Cellobiose inhibits xynA at high concentrations. Optimum pH is 3.0-4.5. Optimum temperature is 55 degrees Celsius. Belongs to the glycosyl hydrolase 7 (cellulase C) family. Was originally identified as a 1,4-beta-D-xylan xylanohydrolase (PubMed:12664153). However, further sequence comparisons and enzymatic studies showed that xynA was principally an 1,4-beta-D-glucan cellobiohydrolase (PubMed:22776993).