A fusion protein having a non-immunoglobulin polypeptide having a cysteine residue proximal to the C terminal thereof, and an immunoglobulin component with a mutated hinge region is provided. The mutation comprises a point mutated site corresponding in position to the position in a native hinge region of the cysteine residue located nearest the cysteine residue of the non-Ig component. The distance from the cysteine residue of the non-immunoglobulin polypeptide and any remaining cysteine residues of the mutated hinge region is sufficient to prevent the formation of a disulphide bond therebetween.