Figure 2.

A schematic representation of spin variables mapped to a 20-residue protein to highlight cooperative units in Ising-like models. Up and down arrow spins represent residues that are folded and unfolded respectively. (A) An example spin-state without windowing. Since each residue can be folded or unfolded independently, there are 2²⁰ possible spin-states. (B and C) Two example spin-states with a 5-residue windowing scheme. The number of accessible spin-states is reduced to 2⁴. (D) For a single sequence approximation, only one consecutive region can be in a folded state, although its length is not restricted. Higher sequence approximations can also be made.