Chimeric polypeptides having xylose isomerase activity

1. A chimeric polypeptide having a xylose isomerase activity, the chimeric polypeptide comprising an amino acid sequence having at least 95% sequence identity with an amino acid sequence of SEQ ID NO: 1,

wherein the chimeric polypeptide further comprises:

a. the amino acids VXW[GP]GREG[YSTA] present at positions 188-196, wherein “X” is any amino acid and wherein amino acids in brackets indicate that one of the bracketed amino acids can be present at that position; and

b. the amino acids [LIVM]EPKPX[EQ]P present at positions 233-240, wherein “X” can be any amino acid and wherein amino acids in brackets indicates that one of the bracketed amino acids can be present at that position; and

c. a His residue at position 103, an Asp residue at position 106, and an Asp residue at position 341;

wherein the positions refer to positions in the reference amino acid sequence of SEQ ID NO: 11.

2. A polynucleotide having a nucleotide sequence encoding the amino acid sequence of claim 1 .

3. The polynucleotide of claim 2 , wherein the nucleotide sequence is codon optimized.

4. A vector comprising the polynucleotide of claim 2 .

5. A method of producing ethanol comprising contacting a source material comprising xylose with the polypeptide of claim 1 .

6. A method of synthesizing the chimeric polypeptide of claim 1 comprising:

a. providing at least two or more parent polynucleotide sequences, a linearized vector capable of replication in yeast, and a yeast cell;

b. transforming the yeast cell with the at least two parent polynucleotide sequences and the linearized vector and wherein the parent polynucleotide sequences undergo recombination forming a chimeric polynucleotide encoding the chimeric polypeptide of claim 1 ; and

c. screening the transformed yeast cells for said recombination wherein said chimeric polynucleotide encodes said chimeric polypeptide.