Fusion of liposomes due to transient and lasting perturbation induced by synthetic amphiphilic peptides

The membrane-fusion activities of amphiphilic peptides of H-(Leu-Aib-Lys-Aib-Aib-Lys-Aib)n-Ala-N(C18H37)2 (n = 1, P7D and n = 3, P21D) immobilized on liposome were investigated. P7D, which takes a random conformation, induced fusion of DPPC SUV, but P7D immobilized on the DPPC SUV did not show the fusion activity. On the other hand, P21D showed a high activity of membrane fusion either in the free peptide or in the immobilized state. CF-Leakage experiments revealed that the peptides caused a transient perturbation of the membrane structure on binding to the membrane. A lasting and steady perturbation was also caused by P21D embedded in the membrane, which was indicated by EU3+ permeation through the membrane. This type of membrane perturbation was very slight in the case of P7D embedded in the membrane. A conclusion was reached that the different activities in the membrane fusion are based on the transient perturbation in the membrane at the peptide binding to the membrane surface as well as the steady perturbation caused by the peptide embedded in the membrane.

Interaction of gramicidin S analogs with lipid bilayer membrane

One of the side chains of Orn residues in gramicidin S (GS) was connected with alanine (AGS), sarcosine (SGS), or histidine (HGS) residue, aiming at developing membrane-active artificial enzymes by virtue of the membrane-associating property of GS. The conformation of the GS analogs was similar to that of GS. However, the affinity of GS and its analogs for dipalmitoylphosphatidylcholine (DPPC) vesicles decreased in the order of GS greater than SGS greater than HGS congruent to AGS. The addition of GS analogs at 10 microM to DPPC vesicles decreased the membrane fluidity, indicating that GS analogs did not disrupt the vesicular structure of DPPC vesicles. On the other hand, GS analogs enhanced carboxyfluorescein-leakage from DPPC vesicles. It was therefore considered that the GS analogs induced the phase-separation of the lipid bilayer membrane. Hydrolytic reactions of HGS in the presence of DPPC vesicles were studied using N-methylindoxyl alkanoate as substrate. HGS reacted only with N-methylindoxyl hexanoate below the phase-transition temperature of the membrane. The substrate specificity of HGS was ascribed to the condensation of HGS in the neighbourhood of the substrate in the lipid bilayer membrane due to the phase-separation below the phase-transition temperature of the membrane.

Hydrolytic reaction catalyzed by poly[N-(substituted)glycine]s having imidazolyl groups in side chains in the presence of liposome

Hydrolytic reactions in the presence of liposomes catalyzed by N epsilon-benzyloxycarbonylhistidine groups introduced into the side chains of poly[N-(3-aminopropyl)glycine] were studied. On increasing the hydrophobicity of the polypeptide catalyst by introducing dodecyl groups into the side chains, and in the presence of dipalmitoylphosphatidylcholine (DPPC) bilayer membranes, p-nitrophenyl palmitate (PNPP) was hydrolyzed more rapidly than p-nitrophenyl acetate (PNPA). The addition of cholesterol or phosphatidylserine to lipid bilayer membranes accelerated the hydrolysis of PNPP catalyzed by the polypeptide catalyst more strongly than that of PNPA. The substrate selectivity and catalytic efficiency of the polypeptide catalyst were found to be controlled by the physical state of the lipid bilayer membranes.