Engineering the hydrophobic residues of a GH11 xylanase impacts its adsorption onto lignin and its thermostability.

This study aimed to characterise the parameters governing the non-specific adsorption of a xylanase from Thermobacillus xylanilyticus (Tx-Xyn11) onto lignin isolated from maize stems. Such adsorption may be due to hydrophobic interactions between Tx-Xyn11 and lignin. Our strategy was to mutate hydrophobic residues present on the surface of Tx- Xyn11 into non-hydrophobic residues. Three mutants (P1, P2, and P3) with altered hydrophobic regions were produced and characterised. The thermostability of the P1 mutant was largely decreased compared with the thermostable Tx-Xyn11. The rate of adsorbed enzyme onto lignin was reduced to a similar extent for the P1 and P2 mutants, whereas the adsorption of the P3 mutant was less affected compared with that of Tx-Xyn11. When considered separately, the hydrophobic residues did not affect xylanase adsorption onto lignin. The addition of Tween 20 also led to the decreased adsorption of Tx-Xyn11 onto lignin. These results suggest that hydrophobic interactions are a key parameter in the interaction of Tx-Xyn11 with isolated lignin.