The invention provides fusion proteins having improved bioactivity comprising a first polypeptide fusion partner and a second polypeptide fusion partner wherein the first fusion partner is linked to the second fusion partner by a mucin-domain polypeptide linker and wherein the bioactivity of the fusion protein of the invention is improved as compared to fusion of the first polypeptide fusion partner and the second polypeptide fusion partner in the absence of the mucin-domain polypeptide linker. Mucin-domain polypeptide linkers comprise a mucin domain that is rich in potential glycosylation sites, and has a high content of serine and/or threonine and proline, which can represent greater than 40% of the amino acids within the mucin domain and further comprise at least about 60% of its mass due to the glycans.

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