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1. (WO2010075194) PROKARYOTIC EXPRESSION OF SOLUBLE, ACTIVE DKK
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What is claimed is:

1. A method for producing soluble, active Dickkopf (Dkk) protein, or a fragment thereof, comprising a) growing a culture of prokaryotic host cells that express all or a portion of a dkk protein encoded by an expression construct; b) isolating said prokaryotic host cells; c) lysing said prokaryotic host cells; d) isolating the soluble portion of said prokaryotic cell lysate; and e) purifying said dkk protein from said soluble portion thereby for producing soluble, active Dickkopf

(Dkk) protein, or a fragment thereof.

2. The method of claim 1, wherein step (a) includes adding isopropyl-1-thio-β-D-galactoside to the culture of prokaryotic host cells.

3. The method of claim 1, wherein all or a portion of the dkk protein is expressed as part of a fusion protein.

4. The method of claim 3, wherein the fusion protein comprises a protein purification tag or a solubilization molecule, or a combination thereof.

5. The method of claim 4, wherein the fusion protein further comprises one or more cleavage sequences.

6. The method of claim 1, wherein the expression construct comprises a portion of the dkk coding sequence and said portion comprises only one cysteine-rich domain.

7. The method of claim 6, wherein said cysteine-rich domain is the carboxy-terminal cysteine-rich domain.

8. The method of claim 1, wherein said expression construct is derived from a prokaryotic expression vector.

9. The method of claim 8, wherein said prokaryotic expression vector is pET32a.

10. The method of claim 1, wherein said dkk protein is selected from the group consisting of dkk-1, dkk-2, dkk-3 and dkk-4.

11. The method of claim 10, wherein said dkk protein is dkk-2.

12. The method of claim 1, wherein said prokaryotic host cells have a mutation in the TrxB gene, the gor gene or both said TrxB gene and said gor gene .

13. The method of claim 12, wherein said prokaryotic host cells further have a mutation in the lacYl gene.

14. The method of claim 1, wherein the isolation step (d) is carried out by centrifugation.

15. The method of claim 1, wherein said purification step (e) comprises the use of a metal chelate column.

16. The method of claim 1, wherein said purification step (e) comprises an HPLC step.

17. An expression construct comprising nucleic acids encoding all or a portion of Dickkopf (dkk) -2.

18. The expression construct of claim 17, wherein the dkk-2 protein is part of a fusion protein.

19. The expression construct of claim 18, wherein the fusion protein comprises a protein purification tag or a solubilization molecule, or a combination thereof.

20. The expression construct of claim 17, wherein said dkk-2 protein is soluble when expressed in a prokaryotic host cell.

21. An expression construct comprising nucleic acids encoding a portion of a dkk protein, wherein said expression construct is present in a prokaryotic host cell and wherein said portion comprises only one cysteine-rich domain of the dkk protein.

22. The expression construct of claim 21, wherein said dkk gene is the dkk-2 gene.

23. The expression construct of claim 21, wherein said cysteine-rich domain is the C-terminal cysteine-rich domain of the dkk protein.

24. The expression construct of claim 21, wherein said portion of the dkk protein is expressed as a fusion protein.

25. The expression construct of claim 21, wherein the dkk protein is soluble when expressed in a prokaryotic host cell.

26. A prokaryotic host cell comprising an expression construct encoding all or a portion of dkk-2 protein.

27. The prokaryotic host cell of claim 26, wherein said prokaryotic host cell has a mutation in the TrxB gene, the gor gene or both said TrxB gene and said gor gene.

28. A prokaryotic host cell comprising an expression construct encoding a portion of dkk in said cell, wherein said portion comprises only one cysteine-rich domain of dkk.