However, β-strands are rarely perfectly extended; rather, they exhibit a twist. The energetically preferred dihedral angles near ("φ", "ψ") = (–135°, 135°) (broadly, the upper left region of the Ramachandran plot) diverge significantly from the fully extended conformation ("φ", "ψ") = (–180°, 180°). The twist is often associated with alternating fluctuations in the dihedral angles to prevent the individual β-strands in a larger sheet from splaying apart. A good example of a strongly twisted β-hairpin can be seen in the protein BPTI.