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Biophys. J. BioFAST: First Published August 19, 2005. doi:10.1529/biophysj.105.059311
© 2005 by the Biophysical Society.

A more recent version of this article appeared on November 1, 2005.
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MEMBRANES

Morphological Behavior of Lipid Bilayers Induced by Melittin Near the Phase Transition Temperature

Shuichi Toraya 1, Takashi Nagao 2, Kazushi Norisada 2, Satoru Tuzi 2, Hazime Saito 2, Shunsuke Izumi 3 and Akira Naito 1*

1 Yokohama National University
2 Himeji Institute of Technology
3 Hiroshima University

* To whom correspondence should be addressed. E-mail: naito{at}ynu.ac.jp.

Submitted on January 10, 2005
Revised on March 14, 2005
Accepted on 4 August 2005


  Abstract
Morphological changes of DMPC, DLPC and DPPC bilayers containing melittin (lecithin to melittin molar ratio of 10:1) around the gel-to-liquid crystalline phase transition temperatures (Tc) were examined by a variety of biophysical methods. First, giant vesicles with the diameters of {approx}20 µm were observed by optical microscopy for melittin-DMPC bilayers at 27.9 °C. When the temperature was lowered to 24.9 °C (Tc=23 °C for the neat DMPC bilayers), the surface of vesicles became flurry and dynamic pore formation was visible in the microscopic picture taken at different exposure times. Phase separation and association of melittin molecules in the bilayers were further detected by fluorescent microscopy and mass spectrometry, respectively. These vesicles disappeared completely at 22.9 °C. It was thus found that the melittin-lecithin bilayers reversibly undergo their fusion and disruption near at the respective Tc. The fluctuation of lipids is, therefore, responsible for the membrane fusion above the Tc and the association of melitin molecules causes membrane fragmentation below the Tc. Subsequent magnetic alignments were observed by solid-state 31P NMR spectra for the melittin-lecithin vesicles at a temperature above the respective Tc. On the other hand, additional large amplitude motion induced by melittin at a temperature near the Tc breaks down the magnetic alignment.

Key Words: Magnetically oriented vesicle, Mass spectrometry, Membrane fusion, Membrane lysis, Optical microscopy, Solid-state NMR




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Copyright © 2005 by the Biophysical Society.