ORIENTATION OF FUSION-ACTIVE SYNTHETIC PEPTIDES IN PHOSPHOLIPID-BILAYERS - DETERMINATION BY FOURIER-TRANSFORM INFRARED-SPECTROSCOPY

A group of synthetic peptides having an amino acid sequence related to the N-terminal region of the influenza virus hemagglutinin HA-2 chain can induce phospholipid membrane fusion in a pH-dependent manner. The se peptides bind to membranes to form alpha-helices even at pH's where no fusion activity is seen. We determined the orientation of these al pha-helical peptides in lipid multibilayers using attenuated total ref lection infrared spectroscopy and found that the peptide alpha-helices took a preferential orientation, the helix axis being about 70-degree s from the normal of the membrane plane, or in other words rather para llel to the membrane plane. The orientation was almost independent of pH and a modification of the N-terminal amino group which reduced the fusion activity of the peptides. The determination was carried out for peptides in lipid multibilayers in dry or hydrated (membranes equilib rated with D2O vapor) conditions. Although a slight decrease in the he lix orientation angle from the membrane normal was noticed for a hydra ted system, the difference between the results for dry and hydrated co nditions was small.