The 30 amino acid peptide GLP-1 has been integrated into the stable host protein human calbindin D9k. The fusion protein binds to GLP-1R. The fusion protein agents can be useful for both diabetes treatment and GLP-1R receptor targeting MR imaging. The fusion protein comprises a first peptide that selectively binds to a site of a target cell and linked to a second peptide, where the fusion protein is more stable than the first peptide alone and may further comprise a detectable label. The first peptide of the fusion protein may be glucagon-like peptide-1 (GLP-1), glucagon-like peptide-1 (GLP-1)(7-36), or glucagon-like peptide-1 (GLP-1) (9-36), or a conservative variant thereof.
