Abstract: A composite polypeptide, said composite polypeptide comprising a desired polypeptide and an expression enhancing domain (“EED”), said EED comprising first and second cysteine amino acid residues Cys1 and Cys2, respectively, Cys1 being located closer to the N-terminus of the composite polypeptide molecule than Cys2, wherein Cys1 and Cys2 are separated by a polypeptide linker, said linker—being free of cysteine and proline;—defining a length sufficient to allow Cys1 and Cys2 to engage in an intramolecular disulfide bond with one another; and—having a flexible polypeptide conformation essentially free of secondary polypeptide structure in aqueous solution, wherein at least one of Cys1 and Cys2 is derivatized with a derivatization moiety.