Studies on Hydrogen Bonds Part V-Hydrogen Bonding in Energy Minimization Studies of Peptides

Abstract

An energy term, representing the N—H…O type of hydrogen bond, which is a function of the hydrogen bond length (R) and angle (θ) has been introduced in an energy minimization program, taking into consideration its interpolation with the non-bonded energy for borderline values of R and θ. The details of the mathematical formulation of the derivatives of the hydrogen bond function as applicable to the energy minimization have been given. The minimization technique has been applied to hydrogen bonded two and three linked peptide units (γ-turns and β-turns), and having Gly, Ala and Pro side chains. Some of the conformational highlights of the resulting minimum energy conformations are a) the occurrence of the expected 4⇒1 hydrogen bond in all of the β-turn tripeptide sequences and b) the presence of an additional 3⇒1 hydrogen bond in some of the type I and II tripeptides with the hydrogen bonding scheme in such type I β-turns occurring in a bifurcated form. These and other conformational features have been discussed in the light of experimental evidence and theoretical predictions of other workers.