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Toxins 2013, 5(4), 637-664; doi:10.3390/toxins5040637

Multiple Membrane Interactions and Versatile Vesicle Deformations Elicited by Melittin

1 Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan 2 Department of Biomedical Information, Division of Biosystems, Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, 2-3-10 Kanda-Surugadai, Chiyoda, Tokyo 101-0062, Japan 3 Department of Applied Physics, Graduate School of Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603, Japan 4 Structural Biology Research Center, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan
* Author to whom correspondence should be addressed.
Received: 18 February 2013 / Revised: 2 April 2013 / Accepted: 10 April 2013 / Published: 17 April 2013
(This article belongs to the Special Issue Pore-Forming Toxins)
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Melittin induces various reactions in membranes and has been widely studied as a model for membrane-interacting peptide; however, the mechanism whereby melittin elicits its effects remains unclear. Here, we observed melittin-induced changes in individual giant liposomes using direct real-time imaging by dark-field optical microscopy, and the mechanisms involved were correlated with results obtained using circular dichroism, cosedimentation, fluorescence quenching of tryptophan residues, and electron microscopy. Depending on the concentration of negatively charged phospholipids in the membrane and the molecular ratio between lipid and melittin, melittin induced the “increasing membrane area”, “phased shrinkage”, or “solubilization” of liposomes. In phased shrinkage, liposomes formed small particles on their surface and rapidly decreased in size. Under conditions in which the increasing membrane area, phased shrinkage, or solubilization were mainly observed, the secondary structure of melittin was primarily estimated as an α-helix, β-like, or disordered structure, respectively. When the increasing membrane area or phased shrinkage occurred, almost all melittin was bound to the membranes and reached more hydrophobic regions of the membranes than when solubilization occurred. These results indicate that the various effects of melittin result from its ability to adopt various structures and membrane-binding states depending on the conditions.
Keywords: melittin; membrane-deformation; giant unilamellar liposome; real-time imaging; spectroscopic analysis melittin; membrane-deformation; giant unilamellar liposome; real-time imaging; spectroscopic analysis
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Takahashi, T.; Nomura, F.; Yokoyama, Y.; Tanaka-Takiguchi, Y.; Homma, M.; Takiguchi, K. Multiple Membrane Interactions and Versatile Vesicle Deformations Elicited by Melittin. Toxins 2013, 5, 637-664.

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