Xylanase is an enzyme important for breaking down xylan into xylose, but xylose can inhibit its function. Scientists evolved a xylose-tolerant xylanase variant by making random mutations in the xylanase gene. They found that the best mutant had three specific mutations that improved its ability to work in the presence of xylose. This mutant had a higher tolerance to xylose, better catalytic capability, and increased enzyme activity compared to the original xylanase. The mutations also affected the structure of the enzyme, making it more efficient at breaking down xylan.