Filipin Orientation Revealed by Linear Dichroism. Implication for a Model of Action

• Published in: Journal of the American Chemical Society Vol. 126; no. 17; pp. 5396 - 5402
• Main Authors: Lopes, Sílvia C. D. N, Goormaghtigh, Erik, Costa Cabral, Benedito J, Castanho, Miguel A. R. B
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 05.05.2004
• Subjects: Anisotropy; Artificial membranes and reconstituted systems; Biological and medical sciences; Cholesterol - metabolism; Filipin - chemistry; Filipin - metabolism; Fluorescence Polarization; Fundamental and applied biological sciences. Psychology; Lipid Bilayers - chemistry; Membrane physicochemistry; Molecular biophysics; Molecular Conformation; Molecular Structure; Spectroscopy, Fourier Transform Infrared; Spectrum Analysis; Structure-Activity Relationship; Phospholipid; Molecular interaction; Artificial membrane; Macrolide; Cholesterol; Fluorescence spectrometry; Filipin; Antibiotic; Antifungal agent; Molecular orientation; Molecular assembly; Polyenic compound; Dichroism
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja031782+

The organization of the polyene antibiotic filipin in membranes containing cholesterol is a controversial matter of debate. Two contradictory models exist, one suggesting a parallel and the other perpendicular organization of filipin with respect to the plane of the membrane. UV−vis linear dichroism, ATR-FTIR, and fluorescence anisotropy decay techniques were combined to study the orientation of filipin in model systems of membranes composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) or 1,2-palmitoyl-sn-glycero-3-phosphocholine (DPPC) with and without cholesterol. Filipin's orientation is determined by the presence/absence of cholesterol when it is inserted in gel crystalline phase model membranes. When cholesterol (33%) is present in DPPC bilayers, filipin stands perpendicular to the membrane surface as expected in “pore-forming” models. At variance, absence of cholesterol leaves filipin in an essentially random organization in the lipidic matrix. In liquid crystalline phase bilayers (POPC) filipin's orientation is perpendicular to the membrane surface even in absence of cholesterol. Thus filipin's activity/organization depends not only on cholesterol presence but also in the lipid phase domain it is inserted in. These findings were combined with spectroscopy and microscopy data in the literature, solving controversial matters of debate.