ABSTRACT
The affinity of amphidinol 3 (AM3) to phospholipid membranes in the presence and absence of sterol was examined by surface plasmon resonance (SPR) experiments. The results showed that AM3 has 1000 and 5300 times higher affinity for cholesterol- and ergosterol-containing liposomes, respectively, than those without sterol. The two-state reaction model well reproduced the sensor grams, which indicated that the interaction is composed of two steps, which correspond to binding to the membrane and internalization to form stable complexes.
Subject(s)
Alkenes/chemistry , Cholesterol/chemistry , Ergosterol/chemistry , Liposomes/chemistry , Pyrans/chemistry , Surface Plasmon Resonance , Sterols/chemistryABSTRACT
Amphidinols (AMs) are a group of dinoflagellate metabolites with potent antifungal activity. As is the case with polyene macrolide antibiotics, the mode of action of AMs is accounted for by direct interaction with lipid bilayers, which leads to formation of pores or lesions in biomembranes. However, it was revealed that AMs induce hemolysis with significantly lower concentrations than those necessary to permeabilize artificial liposomes, suggesting that a certain factor(s) in erythrocyte membrane potentiates AM activity. Glycophorin A (GpA), a major erythrocyte protein, was chosen as a model protein to investigate interaction between peptides and AMs such as AM2, AM3 and AM6 by using SDS-PAGE, surface plasmon resonance, and fluorescent-dye leakages from GpA-reconstituted liposomes. The results unambiguously demonstrated that AMs have an affinity to the transmembrane domain of GpA, and their membrane-permeabilizing activity is significantly potentiated by GpA. Surface plasmon resonance experiments revealed that their interaction has a dissociation constant of the order of 10 microM, which is significantly larger than efficacious concentrations of hemolysis by AMs. These results imply that the potentiation action by GpA or membrane integral peptides may be due to a higher affinity of AMs to protein-containing membranes than that to pure lipid bilayers.
Subject(s)
Alkenes/chemistry , Antifungal Agents/chemistry , Cell Membrane Permeability , Dinoflagellida/chemistry , Erythrocyte Membrane/chemistry , Lipid Bilayers/chemistry , Pyrans/chemistry , Animals , Glycophorins/chemistry , Humans , Liposomes/chemistry , Surface Plasmon ResonanceABSTRACT
Amphidinols (AMs) are a new class of polyhydroxyl polyene compounds with potent antifungal activity. Membrane-permeabilizing activities of AM2, AM3, and AM6 were examined using fluorescent-dye leakage experiments with various phosphatidylcholines (PCs) and sterols. All the AMs tested showed the potent activity to cholesterol-containing liposomes. In the absence of the sterol, AM2, AM3, and AM6 had no membrane-permeabilizing activities to membranes of saturated PC. In liposomes consisting of unsaturated PC, AM2, which possesses an additional ether ring in a polyhydroxyl chain, showed membrane-permeabilizing activities with a moderate efficacy, while AM3 or AM6 did not. The potentiation by sterols was prominent even at 0.5% (wt/wt) and structure-dependent, which ruled out the possibility that alteration of the membrane physical properties induced by sterol was chiefly responsible for this sterol effect. The finding that their activity was not affected by membrane thickness implies that AMs permeabilized membrane by a different mechanism from that of polyene macrolide antibiotics.
Subject(s)
Alkenes/pharmacology , Cell Membrane Permeability/drug effects , Lipids/pharmacology , Pyrans/pharmacology , Antifungal Agents , Fatty Alcohols/pharmacology , Liposomes , Phosphatidylcholines , Polyenes/pharmacology , Sterols/pharmacologyABSTRACT
Two new homologues of amphidinols (AM14 and AM15) were isolated from the cultured dinoflagellate Amphidinium klebsii. The structures were elucidated on the basis of 2D NMR and collision-induced dissociation MS/MS and turned out to be closely related homologues of AM7. Their weak membrane-disrupting activity indicates that the hydrophobic polyene chain is essential for the potent biological activities. Structure-activity relationship for the polyhydroxyl part was then examined with use of AM homologues possessing various chain lengths, indicating that the pore size of the channel/lesion formed by AMs was not greatly affected by the length of the polyhydroxyl chain.
