THE INTERFACIAL REGION OF DIPALMITOYLPHOSPHATIDYLCHOLINE BILAYERS IS PERTURBED BY FUSOGENIC AMPHIPATHS

Citation
Br. Lentz et al., THE INTERFACIAL REGION OF DIPALMITOYLPHOSPHATIDYLCHOLINE BILAYERS IS PERTURBED BY FUSOGENIC AMPHIPATHS, Biophysical journal, 71(6), 1996, pp. 3302-3310
Citations number
29
Categorie Soggetti
Biophysics
Journal title
ISSN journal
00063495
Volume
71
Issue
6
Year of publication
1996
Pages
3302 - 3310
Database
ISI
SICI code
0006-3495(1996)71:6<3302:TIRODB>2.0.ZU;2-#
Abstract
Several structural methods were used to probe the influence of three f usogenic and four nonfusogenic amphipaths on large, unilamellar dipalm itoylphosphatidylcholine (DPPC) vesicles. For four of these structural measurements there was a correlation observed between the ability of an amphipath to favor poly(ethylene glycol) (PEG)-induced fusion and t he structural perturbation reported by each method. First, the fluores cence anisotropy of [4-(trimethylamino)phenyl]-6phenyhexa-1,3,5-triene (TMA-DPH), which probes the upper region of the bilayer, decreased in the range of PEG concentrations previously found to cause fusion of m embranes containing fusogenic amphipaths. For nonfusogenic amphipaths, the anisotropy increased monotonically with PEG concentration. The pr operties of similar probes that locate in the hydrophobic core of the bilayer showed no correlation with fusogenicity, nor did the propertie s of probes purported to sense the aqueous surface of the membrane. Se cond, the frequency of the C=O stretch increased and then decreased dr amatically as fusogenic but not nonfusogenic membranes were heated thr ough their phase transition. Third, there was a dramatic increase in t he frequency of the C-O-C ester stretch at the membrane order/disorder phase transition for membranes containing fusogenic amphipaths, twice the increase observed for nonfusogenic amphipaths. The spectral chara cteristics of phosphate, choline, and acyl chain motions showed no suc h correlation with fusogenicity. Finally, calorimetric measurements sh owed that low levels of fusogenic amphipaths eliminated the ''pretrans ition'' (L(beta) --> P-beta') in DPPC membranes, whereas other amphipa ths shifted but did not eliminate this transition. Taken together, the se results indicate that fusogenic amphipaths perturb the interface or ''backbone'' region of the bilayer rather than the hydrophobic core, the headgroup, or the water interface regions of DPPC bilayers.