Microscopic Observations Reveal That Fusogenic Peptides Induce Liposome Shrinkage Prior to Membrane Fusion

To study the mechanisms involved in membrane fusion, we visualized the fusion process of giant liposomes in real time by optical dark-field microscopy. To induce membrane fusion, we used (i) influenza hemagglutinin peptide (HA), a 20-aa peptide derived from the N-terminal fusion peptide region of th...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2004-03, Vol.101 (10), p.3420-3425
Main Authors: Nomura, Fumimasa, Inaba, Takehiko, Ishikawa, Satoshi, Nagata, Miki, Takahashi, Sho, Hotani, Hirokazu, Takiguchi, Kingo, Vale, Ronald D.
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Biochemistry
Biological Sciences
Biophysical Phenomena
Biophysics
Cell membranes
Hemagglutinin Glycoproteins, Influenza Virus - chemistry
Hemagglutinin Glycoproteins, Influenza Virus - genetics
Hemagglutinin Glycoproteins, Influenza Virus - physiology
In Vitro Techniques
Influenza
Lipid bilayers
Lipids
Liposomes
Luminous intensity
Membrane Fusion - physiology
Membranes
Microscopy, Video
Molecular Sequence Data
P branes
Peptides
Phosphatidylcholines - chemistry
Protein Structure, Secondary
Sequence Homology, Amino Acid
String theory
Surface areas
Viral Fusion Proteins - chemistry
Viral Fusion Proteins - genetics
Viral Fusion Proteins - physiology
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Summary:To study the mechanisms involved in membrane fusion, we visualized the fusion process of giant liposomes in real time by optical dark-field microscopy. To induce membrane fusion, we used (i) influenza hemagglutinin peptide (HA), a 20-aa peptide derived from the N-terminal fusion peptide region of the HA2 subunit, and (ii) two synthetic analogue peptides of HA, a negatively (E5) and positively (K5) charged analogue. We were able to visualize membrane fusion caused by E5 or by K5 alone, as well as by the mixture of these two peptides. The HA peptide however, did not induce membrane fusion, even at an acidic pH, which has been described as the optimal condition for the fusion of large unilamellar vesicles. Surprisingly, before membrane fusion, the shrinkage of liposomes was always observed. Our results suggest that a perturbation of lipid bilayers, which probably resulted from alterations in the bending folds of membranes, is a critical factor in fusion efficiency.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.0304660101