Pseudo-prolines: Induction ofcis/trans-conformational interconversion by decreased transition state barriers

Molecular events such as cis/trans isomerization of Xaa-Pro tertiary amide bonds in peptides and proteins are slow on the overall time scale of the formation of a final biostructure and are, therefore, rate limiting. In order to pursue a better understanding of the molecular events underlying such slow interconversions, we applied the recently introduced pseudo-proline (PsiPro) concept as a tool to study the dynamics of Xaa-Pro bonds by determining the kinetics and thermodynamics of cis/trans isomerism. We show that enhanced isomerization rates of tertiary amide bonds prior to a PsiPro unit in short model peptides is due to lowered transition state barriers. In addition, pronounced effects upon the dynamics of the reversible transition between helix I and II of oligoprolines containing one or several PsiPro units were observed.