MUTANT XYLANASE， MANUFACTURING METHOD AND USE THEREFOR， AND METHOD FOR MANUFACTURING SACCHARIFIED LIGNOCELLULOSE

A mutant xylanase comprising the amino acid sequence of SEQ ID NO: 2 with the following amino acid residue substitutions (B1)， (B2) or (B3): (B1) the asparagine residue at position 33 is substituted by an aspartic acid residue; the glycine residue at position 36 is substituted by an arginine residue; the threonine residue at position 90 is substituted by a serine residue; the glutamine residue at position 132 is substituted by an arginine residue; the leucine residue at position 154 is substituted by a methionine residue; the serine residue at position 174 is substituted by a threonine residue; the proline residue at position 195 is substituted by a histidine residue; the serine residue at position 197 is substituted by an asparagine residue; and the glycine residue at position 217 is substituted by a glutamic acid residue， (B2) the isoleucine residue at position 30 is substituted by a valine residue; the asparagine residue at position 33 is substituted by an aspartic acid residue; the glycine residue at position 36 is substituted by an arginine residue; and the leucine residue at position 154 is substituted by a methionine residue. (B3) the isoleucine residue at position 30 is substituted by a valine residue; the serine residue at position 59 is substituted by a threonine residue; the leucine residue at position 154 is substituted by a methionine residue; the tyrosine residue at position 239 is substituted by a histidine residue; and the cysteine residue at position 242 is substituted by a serine residue， or an amino acid sequence that has a homology of 90% or higher with at least one of (i) the amino acid sequence of SEQ ID NO: 2 with the amino acid residue substitutions (B1)， (ii) the amino acid sequence of SEQ ID NO: 2 with the amino acid residue substitutions (B2)， or (iii) the amino acid sequence of SEQ ID NO: 2 with the amino acid residue substitutions (B3)， and that includes at least one selected from the group consisting of the amino acid residue substitutions (B1)， the amino acid residue substitutions (B2)， and the amino acid residue substitutions (B3); wherein the mutant xylanase is a thermostable xylanase， the thermostable xylanase provides an initial rate of reaction that is at least 70% of that provided by a wild-type xylanase corresponding to the amino acid sequence of SEQ ID NO: 2， and the thermostable xylanase has a xylanase activity after heat treatment at 50 ??C for 24 hours that is at least 50% of its xylanase activity before the heat treatment. The present invention addresses the following problems: providing an inexpensive， efficient lignocellulose saccharification method using a thermostable xylanase; and providing a mutant xylanase that has a substituted amino-acid residue， exhibits stable activity even under harsh conditions in which enzymes are easily deactivated， and has an initial reaction rate not much less than that of the corresponding wild-type xylanase. A lignocellulose saccharification method that includes bringing a lignocellulose feedstock into contact with a thermostable xylanase; and a mutant xylanase that has a substituted amino-acid residue， has an initial reaction rate at least 70% of that of the corresponding wild-type xylanase， and， after a 24-hour heat treatment at 50°C， exhibits xylanase activity at least 50% of that exhibited before said heat treatment.