Sequentially arranged streptavidin-binding modules as affinity tags
The present invention relates to sequentially arranged streptavidin-binding binding modules which may in particular be used as affinity tags. The affinity tags comprise at least two individual modules capable of mediating avidic binding to streptavidin.
1. A fusion protein comprising a streptavidin-binding peptide linked to a protein sequence of interest, wherein the streptavidin-binding peptide comprises a sequential arrangement of two modules, wherein the streptavidin-binding peptide is located at the carboxy terminal end or at the amino terminal end of the protein sequence of interest, wherein each module binds at least one of a streptavidin or a streptavidin mutein, wherein the modules are different or identical and each of the modules comprises an amino acid sequence -His-Pro-Baa- in which Baa is selected from the group consisting of glutamine, asparagine and methionine, and wherein at least one of the modules comprises a sequence -His-Pro-Gln-Phe- (SEQ ID NO:6).
2. The fusion protein according to claim 1 , wherein the protein sequence of interest is selected from the group consisting of a full-length protein, a protein mutant, and a protein fragment.
3. The fusion protein according to claim 1 , wherein each module has a binding affinity of at least Kd≦10 mM.
4. The fusion protein according to claim 1 , wherein at least one module binds competitively with biotin.
5. The fusion protein according to claim 1 , wherein the streptavidin-binding peptide binds cooperatively to a single streptavidin tetramer or streptavidin dimer.
6. The fusion protein according to claim 1 , wherein each module comprises a sequence -His-Pro-Gln-.
7. The fusion protein according to claim 1 , wherein a distance between the at least two modules is between zero amino acids and 50 amino acids, inclusive.
8. The fusion protein according to claim 1 , wherein at least one module comprises a sequence -Oaa-Xaa-His-Pro-Gln-Phe-Yaa-Zaa- (SEQ ID NO:7), where Oaa is Trp, Lys or Arg, Xaa is any amino acid, and wherein either Yaa and Zaa are both Gly, or wherein Yaa is Glu and Zaa is Lys or Arg.
9. The fusion protein according to claim 1 , wherein at least one module comprises a sequence -Trp-Xaa-His-Pro-Gln-Phe-Yaa-Zaa- (SEQ ID NO:8), wherein Xaa is any amino acid, and wherein either Yaa and Zaa are both Gly, or Yaa is Glu and Zaa is Lys or Arg.
10. The fusion protein according to claim 1 , wherein at least one module comprises a sequence -Trp-Ser-His-Pro-Gln-Phe-Glu-Lys- (SEQ ID NO:9).
11. The fusion protein according to claim 1 , which comprises a sequence -Trp-Ser-His-Pro-Gln-Phe-Glu-Lys-(Xaa)n-Trp-Ser-His-Pro-Gln-Phe-Glu-Lys- (SEQ ID NO:3), wherein Xaa is any amino acid, and n is either 8 or 12.
12. The fusion protein according to claim 1 , which comprises a sequence -Trp-Ser-His-Pro-Gln-Phe-Glu-Lys-(GlyGlyGlySer)n-Trp-Ser-His-Pro-Gln-Phe-Glu-Lys- (SEQ ID NO:11), and wherein n is either 2 or 3.
13. The fusion protein of claim 2 wherein said streptavidin binding peptide is located at the carboxy terminal of said protein sequence of interest.
14. The fusion protein of claim 2 wherein said streptavidin binding peptide is located at the amino terminal of said protein sequence of interest.
15. The fusion protein of claim 1 , wherein said sequential arrangement of two modules forms part of a sequential arrangement of 3 modules.
16. The fusion protein of claim 1 , wherein said sequential arrangement of two modules forms part of a sequential arrangement of 4 modules.
17. The fusion protein of claim 1 , wherein said sequential arrangement of two modules forms part of a sequential arrangement of 5 modules.