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Biophys J, October 1998, p. 1869-1873, Vol. 75, No. 4
*Centro de Química-Física Molecular, Complexo I, Instituto Superior Técnico, 1096 Lisboa Codex, Portugal; #Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1700 Lisboa, Portugal; and §Department of Chemical and Nuclear Engineering, University of California, Santa Barbara, California 93106 USA
Filipin is a macrolide polyene with antifungal activity
belonging to the same family of antibiotics as amphotericin B and nystatin. Despite the spectroscopy and electron microscopy studies of
its interaction with natural membranes and membrane model systems, several aspects of its biochemical action, such as the role of membrane sterols, remain to be completely understood. We have used
atomic force microscopy (AFM) to study the effect of filipin on
dipalmitoylphosphatidylethanolamine bilayers in the presence and
absence of cholesterol. The bilayers were prepared by Langmuir-Blodgett deposition over mica and imaged under water. It was shown that filipin-induced lesions could only be found in membranes with cholesterol. In close agreement with electron microscopy results, we
have reported the presence of densely packed circular protrusions in
the membrane with a mean diameter of 19 nm (corrected for convolution with AFM tip) and 0.4 nm height. Larger circular protrusions (90 nm
diameter and 2.5 nm height) and doughnut-shaped lesions were also
detected. These results demonstrate that filipin-induced lesions in
membranes previously observed by electron microscopy are not biased by
artifacts resulting from sample preparation. Filipin aggregates in
aqueous solution could also be imaged for the first time. These
polydisperse spherical structures were observed in samples with and
without cholesterol.
Biophys J, October 1998, p. 1869-1873, Vol. 75, No. 4
© 1998 by the Biophysical Society 0006-3495/98/10/1869/05 $2.00
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