PH-INDUCED DESTABILIZATION OF LIPID BILAYERS BY A LIPOPEPTIDE DERIVEDFROM INFLUENZA HEMAGGLUTININ

A synthetic twenty-one amino acid peptide (AcE4K) based on the amino a cid sequence of the influenza HA2 fusion peptide was coupled to a dist earoylglycerol lipid anchor by amidation of an N-terminal lysine side chain. The secondary structure of Lipo-AcE4K incorporated into POPC (1 -palmitoyl-2-oleoyl-sn-phosphatidylcholine) liposomes was not measurab ly affected by pH, but increased membrane penetration was indicated by tryptophan fluorescence. At outer monolayer concentrations up to 10 m ol%, Lipo-AcE4K formed stable liposomes with POPC and EPC/Chol (egg ph osphatidylcholine/cholesterol) (55:45) at pH 7.5. Acid-induced destabi lization and fusion of these vesicles were demonstrated by fluorescent lipid mixing and contents leakage assays, and by freeze-fracture elec tron microscopy. Membrane destabilization increased with increasing li popeptide concentrations, decreasing pH, inclusion of cholesterol, and incorporation of lipopeptide into the inner monolayer as well as the outer monolayer of the liposomes. Fusion of liposomes bearing Lipo-AcE 4K with erythrocyte ghosts was demonstrated by lipid mixing and fluore scence microscopy.