Role of secondary motifs in fast folding polymers: a dynamical variational principle.

A fascinating and open question challenging biochemistry, physics, and even geometry is the presence of highly regular motifs such as alpha helices in the folded state of biopolymers and proteins. Stimulating explanations ranging from chemical propensity to simple geometrical reasoning have been invoked to rationalize the existence of such secondary structures. We formulate a dynamical variational principle for selection in conformation space based on the requirement that the backbone of the native state of biologically viable polymers be rapidly accessible from the denatured state. The variational principle is shown to result in the emergence of helical order in compact structures.