The present invention is directed to a fusion protein comprising a light chain region of a Clostridial neurotoxin and a heavy chain region of a Clostridial neurotoxin, where the light and heavy chain regions are linked by a disulfide bond. The fusion protein also has a single chain antibody positioned upstream of the light chain region, where the single chain antibody possesses antigen-binding activity. Also disclosed are therapeutic agents, treatment methods, propeptide fusions, isolated nucleic acid molecules, expression systems, host cells, and methods of expressing fusion proteins.
