Production of proteins and polypeptides

1. A fusion protein comprising

(i) at least one solubility-enhancing moiety, wherein each solubility-enhancing moiety has at least 90% identity to the amino acid sequence of SEQ ID NO:6; and

(ii) at least one moiety which is a desired non-spidroin protein or a desired non-spidroin polypeptide, wherein the desired non-spidroin protein or the desired non-spidroin polypeptide is selected from the group consisting of amyloid-forming proteins, amyloid-forming polypeptides, surfactant protein B (SP-B), variants of SP-B containing disulphide, apolipoproteins, membrane proteins, membrane polypeptides, protein drugs, polypeptide drugs, aggregation-prone proteins, aggregation-prone polypeptides, and proteases,

wherein the desired non-spidroin protein or the desired non-spidroin polypeptide has less than 30% identity to any of the amino acid sequences of SEQ ID NO: 6-10,

wherein each solubility-enhancing moiety is linked directly or indirectly to the desired non-spidroin protein or the desired non-spidroin polypeptide moiety, and

wherein the desired non-spidroin protein or the desired non-spidroin polypeptide excludes thioredoxin.

2. The fusion protein according to claim 1 , wherein each solubility-enhancing moiety contains from 130 to 160 amino acid residues.

3. The fusion protein according to claim 1 , wherein the fusion protein comprises at least two solubility-enhancing moieties, each being defined as in claim 1 .

4. The fusion protein according to claim 1 , wherein the fusion protein comprises at least two consecutive solubility-enhancing moieties, each being defined as in claim 1 .

5. The fusion protein according to claim 1 , wherein at least one solubility-enhancing moiety is linked directly or indirectly, with intervening sequences selected from linker peptides and/or further solubility-enhancing moieties, to the amino-terminal or the carboxy-terminal end of the at least one desired non-spidroin protein or desired non-spidroin polypeptide moiety.

6. The fusion protein according to claim 5 , wherein at least one solubility-enhancing moiety is linked directly or indirectly, with intervening sequences selected from linker peptides and/or further solubility-enhancing moieties, to the amino-terminal end of the at least one desired non-spidroin protein or desired non-spidroin polypeptide moiety.

7. The fusion protein according to claim 5 , wherein at least one solubility-enhancing moiety constitutes the amino-tenninal and/or the carboxy-terminal end of the fusion protein.

8. The fusion protein according to claim 1 , further comprising

(iii) at least one cleavage site arranged between the at least one desired non-spidroin protein or desired non-spidroin polypeptide moiety and the at least one solubility-enhancing moiety.

9. The fusion protein according to claim 1 , comprising a linker which constitutes a handle for identification and purification of the fusion protein.

10. The fusion protein according to claim 1 , wherein the desired non-spidroin protein or the desired non-spidroin polypeptide is selected from the group consisting of amyloid beta peptide (Aβ-peptide), islet amyloid polypeptide (IAPP), prion protein (PrP), α-synuclein, calcitonin, prolactin, cystatin, atrial natriuretic factor (ATF) and actin; surface protein B (SP-B), mini-BLeu, α-defensins and β-defensins; class A-H apolipoproteins; (LL-37), surfactant protein C (SP-C), SP-C33, SP-C33Leu, Brichos, GFP, neuroserpin; hormones, including erythropoietin (EPO) and growth hormone (GH), and growth factors, including insulin-like growth factor I (IGF-I) and insulin-like growth factor II (IGF-II); avidin and streptavidin; and protease 3C.

11. The fusion protein according to claim 1 , wherein the desired non-spidroin protein or the desired non-spidroin polypeptide is selected from SP-B, mini-B, mini-BLeu, 1a AA, 1b AA, 1a LL and 1b LL, and SP-C, SP-C(Leu), SP-C33, SP-C30, SP-C33(Leu) and KL4.

12. The fusion protein according to claim 11 , wherein the desired non-spidroin protein or the desired non-spidroin polypeptide is mini-BLeu.

13. The fusion protein according to claim 11 , wherein the desired non-spidroin protein or the desired non-spidroin polypeptide is SP-C33Leu.

14. The fusion protein according to claim 1 , selected from the group consisting of the amino acid sequences of SEQ ID NOS 26, 28, 30, 34, 37, 39, 42 and 47; and proteins having at least 95% identity to any one of said amino acid sequences.

15. The fusion protein according to claim 1 , wherein the desired non-spidroin protein or the desired non-spidroin polypeptide is selected from the group consisting of amyloid-forming proteins, amyloid-forming polypeptides, surfactant protein B (SP-B), apolipoproteins, membrane proteins, membrane polypeptides, and proteases.

16. The fusion protein according to claim 1 , wherein the desired non-spidroin protein or the desired non-spidroin polypeptide is selected from the group consisting of aggregation-prone proteins and aggregation-prone polypeptides, wherein the desired non-spidroin protein or the desired non-spidroin polypeptide excludes thioredoxin.

17. The fusion protein according to claim 1 , wherein the desired non-spidroin protein or the desired non-spidroin polypeptide is selected from the group consisting of amyloid beta peptide (Aβ-peptide), islet amyloid polypeptide (IAPP), prion protein (PrP), α-synuclein, calcitonin, prolactin, cystatin, atrial natriuretic factor (ATF) and actin; SP-B, mini-Bleu, α-defensins and β-defensins; class A-H apolipoproteins; (LL-37), surfactant protein C (SP-C), SP-C33, SP-C33Leu, Brichos, GFP, neuroserpin; hormone, insulin-like growth factor I (IGF-I) and insulin-like growth factor II (IGF-II); avidin and streptavidin; and protease 3C.

18. The fusion protein according to claim 17 , wherein the hormone is erythropoietin (EPO) or growth hormone (GH).