This C-terminal Exendin 4 Trp Cage variant is known as TC5b and can be used for simulation studies of protein folding. This 20-residue construct is over 95% folded in water at physiological pH, and exhibits a tightly folded tertiary structure in solution. Trp Cage exhibits a highly stable mini-protein fold. It consists of a short helix, a 3,10 helix and a C-terminal poly-proline that packs against a Trp in the alpha helix. It is known to fold within 4 nanoseconds. This stable fast-folding Trp Cage sequence displays special stabilizing features specific to this miniprotein.