Simulations of the villin headpiece.
The villin headpiece is a small, 36-residue alpha helical protein. It has been heavily studied experimentally and by simulation since is perhaps one of the smallest, fastest folding proteins. It has a hydrophobic core made of 3 phenylalanines, but also has two groups (a tryptophan and another phenylalanine) which are hydrophobic, but are solvent exposed (for functional reasons). Duan and Kollman simulated 1 microsecond of MD time, in a ground breaking simulation.