Effect of amino acid sequence change on peptide-membrane interaction

The RGD region of the (110-121) peptide sequence (FWRGDLVFDFQV) of VP3 capsid protein of hepatitis A virus, which is described to be responsible for a high immunoresponse, was changed for RGE and RKD amino acids in order to analyze the change effect on the physicochemical properties of the peptide. Peptides were synthesized by solid-phase synthesis and characterized by amino acid analysis, analytical high-performance liquid chromatography, and electrospray mass spectrometry. The peptides had surface activity concentration dependent, formed stable monolayers at the air/water interface, and were able to insert into lipid monolayers of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phosphatidylglycerol, phosphatydic acid, L-α-phosphatidyl-L-serine, stearylamine, sphyngomyelin, and liver extract. Differential scanning calorimetry (DSC) was used to investigate the thermotropic phase properties of binary mixtures of DPPC and the three peptides. DSC data showed a complete abolition of DPPC pretransition and significant broadening of the main phase transition with increasing amounts of peptide. These results are indicative of an interfacial location of the peptides and with some penetration of the nonpolar amino acid side chains into the hydrocarbon chain region closer to the polar/nonpolar interface. Finally, fluorescence spectroscopy confirmed the preferential interaction of the peptides with the liquid crystalline state of the bilayer with a contribution of both hydrophobic and electrostatic forces.