| abstract |
Fungal xylanases are disclosed that have been modified to increase thermostability. Thenmodifications are at exposed serine residues or within positions 90 to 160 (inclusive). Thenstarting xylanase is the endo-1,4-β-xylanase I from Aspergillus niger. Single amino acidnsubstitutions are preferred, in the B7, B8 or B9 anti-parallel strands of the β-sheet of thenxylanase. Modifications can be at any of positions 91 to 95, 98, 103, 108 or 155, or at onenor more of the serine residues 22, 27, 48, 49, 55, 59, 61, 173, 179 or 183, and thensubstitution can be a replacement of the original residue by a Cys, Thr, Asn, His, Arg ornAsp residue. Complete DNA and amino acid sequences are disclosed for two of thenmutants, S93L and S59N. The mutations can increase thermostability by more thannten-fold, and as the mutations are on the outside of the molecule, and away from the activensite, they do not adversely affect the xylanase activity and the xylanases are still activenunder highly acidic conditions. |