Intraresidual Correlated Motions in Peptide Chain

Conformational flexibility of polypeptide chains is mainly driven by changes in the (phi, psi) dihedrals of each residue. Such motions, however, are not completely independent, as certain (anti)correlated motions are favored. In this work, we investigate the correlations between the dihedral displacements of adjacent residues, (Δphi i, Δpsi i+1) and (Δphi i-1, Δpsi i), i.e. interresidual, and within the same residue, (Δphi i, Δpsi i), i.e. intraresidual, by analyzing extensive Molecular Dynamics trajectories of initially extended polyalanine chains in detail. Correlations are evaluated individually at different residue conformations covering the whole (phi, psi)-space. From these we draw maps which clearly show how the coupled motions strongly depend on the conformation, thus unveiling an unprecedented strong intramolecular correlation displaying opposite (correlated/anticorrelated) behaviors at different conformations. By developing a tailored model, it is also demonstrated that both inter and intraresidual correlations arise from the propensity of the peptide to minimize the overall atomic displacements along the whole polypeptide chain.