Glucose dehydrogenase
Disclosed is a water-soluble PQQGDH wherein two subunits are linked together via a disulfide bond. The water-soluble PQQGDH of the invention exhibits improved thermal stability.
1. An isolated mutant water-soluble pyrrolo-quinoline quinine glucose dehydrogenase (PQQGDH) protein, wherein two subunits of said mutant PQQGDH are linked together via one or more disulfide bonds, wherein said mutant PQQGDH is a mutant of a PQQGDH comprising the amino acid sequence of SEQ ID NO:1 and wherein said mutant PQQGDH only has one or more amino acid substitutions selected from the group consisting of:
(1) serine at position 415 is substituted with a cysteine residue in SEQ ID NO:1,
(2) tyrosine at position 414 is substituted with a cysteine residue in SEQ ID NO:1,
(3) aspartate at position 340 is substituted with a cysteine residue in SEQ ID NO:1, and
(4) tyrosine at position 418 is substituted with a cysteine residue in SEQ ID NO:1.
2. The mutant PQQGDH of claim 1 wherein serine at position 415 of the amino acid sequence of SEQ ID NO: 1 is substituted with a cysteine residue.
3. The mutant PQQGDH of claim 1 wherein tyrosine at position 414 of the amino acid sequence of SEQ ID NO: 1 is substituted with a cysteine residue.
4. The mutant PQQGDH of claim 1 wherein tyrosine at position 414 and serine at position 415 of the amino acid sequence of SEQ ID NO: 1 are both substituted with cysteine residues.
5. The mutant PQQGDH of claim 1 wherein aspartate at position 340 and tyrosine at position 418 of the amino acid sequence of SEQ ID NO: 1 are both substituted with cysteine residues.
6. A glucose assay kit comprising the mutant PQQGDH of claim 1 .
7. A glucose sensor comprising the mutant PQQGDH of claim 1 .
8. An isolated mutant PQQGDH protein, wherein two subunits of said mutant PQQGDH are linked together via one or more disulfide bonds, wherein said mutant PQQGDH is a mutant of a PQQGDH comprising the amino acid sequence of SEQ ID NO:1 and wherein said mutant PQQGDH only has the following amino acid substitutions:
(1) serine at position 415 is substituted with a cysteine residue and aspartate at position 167 is substituted with a glutamate residue in SEQ ID NO:1,
(2) serine at position 415 is substituted with a cysteine residue and serine at position 231 is substituted with a lysine residue in SEQ ID NO:1, or
(3) serine at position 415 is substituted with a cysteine residue, aspartate at position 167 is substituted with a glutamate residue and serine at position 231 is substituted with a lysine residue in SEQ ID NO:1.