Effect of sequence‐specific interactions on the stability of helical conformations in polypeptides

A modification of the Zimm–Bragg two‐state model for the helix–coil transition in polypeptides, which considers the effect of charge–dipole, charge–charge, and other specific interactions on helix stability, is presented. The new model introduces a series of adjustable parameters whose values are estimated by fitting to recent spectroscopic results on medium‐sized peptides. This formalism, based on traditional two‐state helix–coil transition models, provides a framework in which data on the helix contents of peptides of specific sequence can be rationalized by a statistical mechanical theory.