Compositions and methods comprising cellulase variants with reduced affinity to non-cellulosic materials

1. An isolated cellulase variant, comprising a sequence that is at least 95% identical to the amino acid sequence of a reference cellobiohydrolase II (CBH2) set forth as SEQ ID NO:3, wherein said variant is a mature form having cellulase activity and comprising a substitution at position 63, wherein the position is numbered by correspondence with the amino acid sequence of SEQ ID NO:3, and wherein the substitution causes the cellulase variant to have a more negative net charge in comparison to the reference CBH2.

2. The isolated cellulase variant of claim 1 , wherein the substitution at position 63 comprises removal of one or more positive charges.

3. The isolated cellulase variant of claim 2 , wherein the removal of one or more positive charges comprises a replacement of an arginine with a neutral amino acid.

4. The isolated cellulase variant of claim 1 , wherein the substitution at position 63 comprises addition of one or more negative charges.

5. The isolated cellulase variant of claim 1 , wherein the substitution at position 63 comprises removal of one or more positive charges and addition of one or more negative charges.

6. The isolated cellulase variant of claim 5 , wherein the removal of one or more positive charges and addition of one or more negative charges comprises a replacement of an arginine with a negatively charged amino acid.

7. The isolated cellulase variant of claim 1 , wherein the variant comprises a further substitution at one or more further positions selected from the group consisting of 146, 151, 189, 208, 211, 244, 277 and 405, wherein the further positions are numbered by correspondence with the amino acid sequence of the reference cellobiohydrolase II (CBH2) set forth as SEQ ID NO:3.

8. The isolated cellulase variant of claim 7 , wherein the further substitution at one or more further positions comprises a replacement of aspartic acid or glutamic acid with a neutral amino acid.

9. The isolated cellulase variant of claim 7 , wherein the further substitution at one or more further positions comprises one or more of the group consisting of D151N, D189N, D211N, D277N, D405N, E146Q, E208Q, and E244Q, wherein the positions are numbered by correspondence with the amino acid sequence of the reference cellobiohydrolase II (CBH2) set forth as SEQ ID NO:3.

10. The isolated cellulase variant of claim 1 , wherein the cellulase variant is derived from a parent cellulase selected from the group consisting of Hypocrea jecorina CBH2, Hypocrea koningii CBH2, Humicola insolens CBH2, Acremonium cellulolyticus CBH2, Agaricus bisporus CBH2, Fusarium osysporum EG, Phanerochaete chrysosporium CBH2, Talaromyces emersonii CBH2, Thermobifida fusca 6B/E3 CBH2, Thermobifida fusca 6A/E2 EG, and Cellulomonas fimi CenA EG.

11. The isolated cellulase variant of claim 1 , wherein the cellulase variant is derived from a parent cellulase whose amino acid sequence is at least 97% identical to a member of the group consisting of SEQ ID NO:3, SEQ ID NO:4, SEQ ID NO:5, SEQ ID NO:6, SEQ ID NO:7, SEQ ID NO:8, SEQ ID NO:9, SEQ ID NO:10, SEQ ID NO:11, SEQ ID NO:12, and SEQ ID NO:13.

12. The isolated cellulase variant of claim 1 , wherein the more negative net charge is a −1 or −2 in comparison to the reference CBH2.

13. A method of converting biomass to sugars comprising contacting said biomass with the cellulase variant of claim 1 .

14. A method of producing a fuel comprising:

contacting a biomass composition with an enzymatic composition comprising the cellulase variant of claim 1 to yield a sugar solution; and

culturing the sugar solution with a fermentative microorganism under conditions sufficient to produce a fuel.