Structural modeling and further improvement in pH stability and activity of a highly-active xylanase from an uncultured rumen fungus

► XynR8 is a cellulase-free xylanase with the highest activity among reported xylanases. ► XynR8 is stable between pH 3.0 to 11.0. ► N41D mutation obviously improves the tolerance of XynR8 to pH2.0. ► N58D mutation enhances both the activity and acid tolerance of XynR8. ► XynR8 and mutants are highly active at a broad range of temperatures and pH.