Flexibility of active center affects thermostability and activity of Penicillium canescens xylanase E

Xylanases are used in several industrial applications, such as feed additives, the bleaching of pulp and paper, and the production of bread, food, and drinks. Xylanases are required to remain active after heat treatment at 80-90 °C for 30 s to several minutes due to the conditions of feed pelleting. Also, xylanases need to be active at 60-70 °C for several hours while bleaching of pulp and paper or manufacturing of bread, food, and drinks is performed. Xylanases of the glycoside hydrolase family GH10 are good candidates for application in such processes because of their high thermostability and, in particular, as feed additives because of their insensitivity to protein inhibitors in cereal feeds. In the study, the thermostability of GH10 xylanase E from Penicillium canescens was improved to reach a half-inactivation period of 2 min at 80 °C compared to 21 s for the wild-type enzyme (WT). Enzymatic activity was increased by 22-48 % at 40-70 °C, which improved the action of the enzyme as a feed additive in the gastric system of animals and during bleaching of pulp and paper. Molecular dynamics simulations demonstrated lower flexibility of the tertiary structure of the engineered enzyme at elevated temperatures compared to WT. The residues W113, Q116, W313, and W321 in the (-1) and (-2) subsites for the substrate binding were less flexible. In the simulations, the engineered enzyme had a comparable content of α-helixes, 3₁₀-helixes, β-sheets, and β-bridges as WT, but a lower content of coils and a higher content of β-turns.