Figure 1.

Illustration of the folding process for a sequence of hydrophobic (H) and polar (P) beads that has one nearest neighbor H—H chain bond (Top) out of a possible six. All sequences in this model contain seven H (dark beads) and nine P (light beads) “residues.” Nearest neighbor residues along the chain are connected by freely jointed string bonds of finite minimum and maximum extension (i.e., a square well potential). Cross chain contacts between pairs of H residues are strongly attractive unless the residues are nearest neighbors in sequence. All other (non-nearest neighbor) pairs of residues interact as hard beads, and all nearest neighbors in sequence interact according to the string potential. The sequences fold into structures with an ordered hydrophobic core surrounded by a liquid-like halo of P residues.