In contrast, Figure shows that both the villin headpiece (PDB: 2F4K) and BPTI (PDB: 5PTI) retain their experimental structures extremely well (average RMSD in the range 1-2 Å). The three α-helices present in the villin headpiece are retained throughout the simulations, and the φ/ψ distributions are in excellent agreement with experiment and the AMBER force field (Figure ). Similarly, in BPTI, regions with helical or β-sheet structures retain their structure. Some small changes in structure are observed (for example, residues 10-12 in villin and 36-40 in BPTI), though these correspond to regions with no fixed secondary structure or a bend.