Single chain FC polypeptides

1. An isolated monovalent polypeptide, comprising a single chain Fc polypeptide, and a monovalent binding domain;

wherein the single chain Fc polypeptide N to C-terminal sequence is:

a first CH2 domain linked via its C-terminus to an N-terminus of a first CH3 domain, and the first CH3 domain is linked at its C-terminus via at least one amino acid linker comprising repeat units of GSGGS (SEQ ID NO:92), GGGGS (SEQ ID NO:93), and GGGS (SEQ ID NO94) to the N-terminus of a second CH2 domain and the second CH2 domain linked at its C-terminus to the N-terminus of a second CH3 domain;

wherein the single chain Fc polypeptide does not contain cysteine amino acid residues in a hinge region;

wherein Fc domains in the single chain Fc polypeptide consist of two CH2 domains and two CH3 domains, wherein the first CH2 domain is intra-molecularly dimerised with the second CH2 domain and the first CH3 domain is intra-molecularly dimerised with the second CH3 domain within the single chain Fc polypeptide;

wherein the two CH2 domains and the two CH3 domains form a functional Fc domain within the single chain Fc polypeptide via at least one linker of 15 to 50 or 30 to 130 amino acids in length, or combinations thereof; and

wherein the single chain Fc polypeptide is linked at its N terminus to one biologically active molecule that is a monovalent binding protein selected from the group consisting of scFv, Fab, Fab', V HH , and Fv,

with the proviso that when the single chain polypeptide Fc is linked to the biologically active molecule via a linker, the linker does not contain cysteine amino acid residues.

2. The polypeptide of claim 1 , wherein the at least one linker forming the functional single chain Fc polypeptide optionally comprises one or more amino acids selected from glycine, serine, alanine and threonine.

3. The polypeptide of claim 2 , wherein the at least one linker forming the functional single chain Fc polypeptide comprises the sequence given in SEQ ID NO:62.

4. The polypeptide of claim 3 , wherein the linker comprises all or part of an antibody hinge sequence or a modified antibody hinge sequence.

5. The polypeptide of claim 1 , wherein the biologically active molecule and the single chain Fc polypeptide are linked by a peptide linker of between 1 and 100 amino acids in length.

6. The polypeptide of claim 1 to which one or more effector molecules are attached.

7. A pharmaceutical composition comprising the single chain Fc polypeptide of claim 1 , in combination with one or more of a pharmaceutically acceptable excipient, diluent or carrier.

8. The pharmaceutical composition of claim 7 , additionally comprising other active ingredients.

9. The polypeptide of claim 1 , wherein the linker is 50 to 100 amino acids in length.