Designing disorder: Tales of the unexpected tails.

Protein tags of various sizes and shapes catalyze progress in biosciences. Well-folded tags can serve to solubilize proteins. Small, unfolded, peptide-like tags have become invaluable tools for protein purification as well as protein-protein interaction studies. Intrinsically Disordered Proteins (IDPs), which lack unique 3D structures, received exponentially increasing attention during the last decade. Recently, large ID tags have been developed to solubilize proteins and to engineer the pharmacological properties of protein and peptide pharmaceuticals. Here, we contrast the complementary benefits and applications of both folded and ID tags based on predictions of ID. Less structure often means more function in a shorter tag.