Helix–coil transition theory including long‐range electrostatic interactions: Application to globular proteins

An extension of the Zimm–Bragg two‐state theory for the helix–coil transition in polypeptides, which takes into account the effect of peptide charge–dipole interactions on helix stability, is presented. This new theory incorporates these interactions in an expression that is parameterized on recently obtained experimental data on polypeptides for which electrostatic effects are known to influence helix content. Unlike previous two‐state or multistate models, which are parameterized on protein x‐ray data, the present theoretical treatment in independent of such protein data. The theoretical model is applied to a series of peptides derived from the C‐peptide of ribonuclease A, which have been the object of recent spectroscopic studies. The new theoretical approach can account for most of the structural information derived from studies of these C‐peptides, and for overall average helix probabilities that are close in magnitude to those observed for these polypeptides in solution. An application of this new formulation for the prediction of the locations of α‐helices in globular proteins from their amino acid sequence is also presented.