Temperature dependence of polypeptide partitioning between water and phospholipid bilayers

Various thermodynamic forces (e.g., the hydrophobic effect, electrostatic interactions, peptide immobilization, peptide conformational changes, ''bilayer effects,'' and van der Waals dispersion forces) call participate in the transfer of polypeptides from aqueous solution into lipid bilayers. To investigate the contributions of these forces to peptide-membrane thermodynamics, we have studied the temperature dependence of the water-bilayer partitioning of 4 polypeptides derived from the first 25 amino acid residues in the presequence of subunit IV of yeast cytochrome c oxidase (Cox IVp) using electron paramagnetic resonance spectroscopy, The partitioning of the Cox Np peptides into phospholipid bilayers increase as the temperature is increased from 3 to 40 degrees C. The contribution of bilayer surface expansion to the temperature-dependent partitioning is estimated to be relatively small and to contribute minimally to the increased bilayer binding of the peptides with increasing temperature, Thermodynamic analysis of the data shows that the transfer of the peptides from water into bilayers at 298 K is driven by the entropic term (-T Delta S-tr) with vaiues ranging from -6.7 to -10 kcal mol(-1), opposed by the enthalpic term (Delta H-tr) by approximately 4 kcal mol(-1), and accompanied by a change in heat capacity (Delta C-p) ranging from -117 to -208 cal K-1 mol(-1). Our results indicate that while a variety of forces do, in fact, contribute to the transfer free energies (Delta G(tr)), the major driving force for the water-to-bilayer transfer is the hydrophobic effect.