Homogeneity and secretion of a recombinant follicle stimulating hormone (FSH) in mammalian systems
A hybrid protein includes two coexpressed amino acid sequences forming a dimer. Each sequence contains the binding portion of a receptor, such as TBP1 or TBP2, or a ligand, such as IL-6, IFN-β and TPO, linked to α subunit of a natural heterodimeric scaffold. Each coexpressed sequence contains a corresponding subunit so as to form a heterodimer upon expression. Corresponding DNA molecules, expression vectors and host cells are also disclosed as are pharmaceutical compositions and a method of producing such proteins.
1. A hybrid protein comprising two different coexpressed amino acid sequences forming a heterodimer, each comprising:
(a) at least one amino acid sequence selected from the group consisting of a chain of a homomeric-receptor, a chain of a heteromeric receptor, a ligand other than a gonadotropin, a fragment of said chain of said homomeric receptor, said chain of said heteromeric receptor, or said ligand, wherein said ligand or fragment thereof retains ligand-receptor binding capability and said chain of said homomeric receptor or fragment thereof, and said chain of said heteromeric receptor or fragment thereof retain ligand-receptor binding capability either alone or in association with a homologous or heterologous chain of said receptor; and
(b) a heterodimeric scaffold which is a subunit of a circulating non-immunoglobulin protein, or a fragment thereof which retains the ability of the subunit to form a heterodimer with other subunits thereof;
wherein sequences (a) and (b) are joined either directly or through a peptide linker, and in which the sequences (b) in each of said two coexpressed sequences aggregate with each other to dimerize and form a heterodimer.
2. A hybrid protein in accordance with claim 1 , wherein said sequence (a) is selected from the group consisting of TNF Binding Protein 1 (TBP1), TNF Binding Protein 2 (TBP2) or a fragment of said TBP1 or TBP2 still containing the ligand binding domain; the extracellular domain of the IFNα/β receptor or the IFNγ receptor; a gonadotropin receptor or extracellular fragments thereof; and IL-6, IFNβ, thromhopoietin (TPO) or fragments thereof.
3. A hybrid protein in accordance with claim 1 , wherein sequence (a) is joined, either directly or via a linker, to the amino terminus of sequence (b).
4. A hybrid protein in accordance with claim 1 , wherein sequence (a) is joined, either directly or via a linker, to the carboxy terminus of sequence (b).
5. A hybrid protein in accordance with claim 1 , wherein said two coexpressed amino acid sequences each include the sequence for TBP1 or a fragment thereof having amino acid residues 20-161 or 20-190 of TBP1, as sequence (a), wherein said two coexpressed amino acid sequences form a heterodimer through sequence (b).
6. A hybrid protein in accordance with claim 1 , wherein said two coexpressed amino acid sequences each include the extracellular domain of a gonadotropin receptor as sequence (a), wherein said two coexpressed amino acid sequences, form a heterodimer through sequence (b).
7. A hybrid protein in accordance with claim 1 , wherein said sequence (a) is the FSH receptor extracellular domain.
8. A hybrid protein in accordance with claim 6 , wherein said sequences (a) and (b) are linked with a peptide linker.
9. A hybrid protein in accordance with claim 8 , wherein said peptide linker has an enzyme cleavage site.
10. A hybrid protein in accordance with claim 9 , wherein said enzyme cleavage site is a thrombin cleavage site.
11. A hybrid protein in accordance with claim 9 , wherein said enzyme cleavage site is recognized and cleaved by an enzyme which is found in the ovary.
12. A hybrid protein in accordance with claim 8 , wherein said peptide linker serves as a flexible hinge.
13. A pharmaceutical composition comprising a hybrid protein in accordance with claim 1 and a pharmaceutically acceptable carrier and/or excipient.
14. The hybrid protein of claim 1 , wherein each of said two coexpressed amino acid sequences forming a heterodimer consists essentially of sequences (a) and (b).
15. A method for inducing follicular maturation, comprising administering to a subject in need thereof a hybrid protein comprising two coexpressed amino acid sequences forming a dimer, each comprising FSH receptor extracellular domain and a subunit of FSH, wherein the FSH receptor extracellular domain and the subunit of FSH are bonded together directly or through a peptide linker, and in which each FSH subunit in each of said coexpressed sequences is capable of aggregating with the other FSH subunit to form a dimer complex.
16. The method of claim 15 , wherein the FSH receptor extracellular domain is linked to the amino terminus of the FSH subunit.
17. The method of claim 15 , wherein the FSH receptor extracellular domain and the subunit of FSH are linked through a peptide linker.
18. The method of claim 17 , wherein the peptide linker has an enzyme cleavage site.
19. The method of claim 18 , wherein the enzyme cleavage site is a thrombin cleavage site.
20. The method of claim 17 , wherein the peptide linker serves as a flexible hinge.