Helical sensors of membrane saturation: Changes in orientation and curvature preference.

The degree of unsaturation in lipids, which refers to the number of double bonds in their acyl chains, influences properties such as fluidity and lipid packing. However, it is not well understood how the unsaturation affects the ability of peptides to sense membrane curvature. In our study, we compared membranes with varying levels of unsaturation: monounsaturated POPC; bis-unsaturated DOPC; and polyunsaturated PAPC. We investigated how these membranes interact with peptides of varying hydrophobicity. Using coarse-grained molecular dynamics simulations, we found that increasing unsaturation leads to deeper peptide insertion into the lipid bilayer, which correlates with a shift in curvature preference toward more negative values. We demonstrate that specific peptides preferentially localize on the positively curved regions in saturated membranes but shift preference to negatively curved regions in unsaturated membranes, thereby functioning as sensors of membrane unsaturation. In addition, polyunsaturated lipids facilitate the reorientation of peptides from a membrane-adsorbed state to a transmembrane state. These findings may play a role in biological processes such as vesicle formation, membrane fusion, and protein sorting and highlight the adaptability of peptides to different lipid compositions in membranes.