Folding Peptides into Lipid Bilayer Membranes.

The adsorption, insertion, and folding of a synthetic 16-residue WALP peptide was studied at physiological time scales (>μs) by atomic detail molecular dynamics simulation using a fully explicit DPPC/DMPC lipid bilayer setup. The temperature was elevated to 80 °C/44 °C respectively to increase sampling. After spontaneous adsorption the peptide crosses the polar interfaces to locate at the hydrophobic bilayer core. Remarkably, insertion occurs before folding, and the dominant configurations are inserted beta-hairpins. For the DPPC simulation a trans-membrane helix formed but was not stable. Unfolded membrane insertion of WALP was first observed by Nymeyer and co-workers using a replica exchange method. However, both results are in stark contrast to current theory and simulations with implicit membrane models, which rule out unfolded insertion into the hydrophobic core. At present the exact reasons for this unexpected behavior cannot be unambiguously determined, due to the lack suitable experimental and simulation data to compare to. Nevertheless, the results demonstrate that simulation studies can now in principle provide atomic detail insights into complex biophysical phenomena at physiologically relevant time scales. Future effort must now concentrate on suitable ways to verify current force fields and methodologies for such simulations.