Energetics of insertion of soluble proteins into membrane

Abstract

A number of soluble proteins that insert into membranes show a characteristic hairpin bent helix-helix pair, which is presumed to play an important role in insertion into the lipid membrane. However, little is known about the energetics of membrane insertion of such proteins. It is predicted that the spontaneous insertion of hydrophobic helical proteins into lipid bilayers is mainly driven by a hydrophobic free-energy and interaction of polar and charged side chains of protein with the solvent. With a consideration of hairpin bent a helix as an 'elliptical frustrum' we have demonstrated that insertion of such bent alpha-helices into the lipid bilayers is an outcome of various free energies like solvation, lipid perturbation, protein immobilization in lipid and packing energy. Different physical origins and different magnitudes of various free energies satisfy this model for insertion into the membranes.