The Nature of the Hydrophobic Binding of Small Peptides at the Bilayer Interface: Implications for the Insertion of Transbilayer Helices

Abstract

One method of obtaining useful information about the physical chemistry of peptide/bilayer interactions is to relate thermodynamic parameters of the interactions to structural parameters obtained by diffraction methods. We report here the results of the application of this approach to interactions of hydrophobic tripeptides of the form Ala-X-Ala-0-tert-butyl with lipid bilayers. The thermodynamic constants (ΔG_t> ΔH_1, and Δ1) for the transfer of the tripeptides from water into DMPC vesicles were determined for X = Leu, Phe, and Trp and found to be consistent with those expected for hydrophobic interactions above the phase transition of DMPC. Combining these results with the earlier ones of Jacobs and White [(1986) Biochemistry 25, 2605-2612], the favorable free energies of transfer with different amino acids in the -X- position increase in the order Gly

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