Factors Affecting the Stabilization of Polyproline II Helices in a Hydrophobic Environment

Several parameters have a critical importance for the stabilization of either polyproline I (PPI) or polyproline II (PPII) helices in a hydrophobic environment. Among them, it was found out that the concentration is crucial as polyprolines at 3 mM concentration stably fold in PPII helices, that are organized in aggregates stable even after several days and are detectable by dynamic light scattering analysis. In more diluted concentration the same molecules stably fold in PPI helices, and no aggregates are found. In contrast, the introduction of a (4S,5R)-4-carboxy-5-methyloxazolidin-2-one (l-Oxd) moiety always inhibits the formation of the PPI helix, regardless of the l-Oxd position and the solution concentration.