S. Girod et al., Relationship between conformation of polysaccharides in the dilute regime and their interaction with a phospholipid bilayer, LUMINESCENC, 16(2), 2001, pp. 109-116
Interactions between polysaccharides and phospholipid bilayers have already
been demonstrated in the literature but little is known about the influenc
e of macromolecule conformations related to the solvent characteristics (pH
, ions, ionic strength). In this study we have investigated the conformatio
n of iono- and thermo-sensitive polysaccharides, iota- and kappa-carrageena
ns, and their interaction with a dimyristoylphosphatidylcholine (DMPC) mode
l bilayer. The study was performed in two different media (NaCl 150 mmol/L,
pH 6.5, and NaCl 300 mmol/L, pH 6.5). In the first part. the iota- and kap
pa-carrageenan samples have been characterized by size exclusion chromatogr
aphy (SEC) coupled with a multi-angle laser light-scattering detector (MALL
S). The SEC-MALLS results clearly show polysaccharide chain association at
high ionic strength. In the second part, the polysaccharide-membrane intera
ction has been studied, using fluorescent probes embedded in the membrane.
The thermotropic properties of the membrane were investigated by fluorescen
ce depolarization of 1-(4-trimethylammonium-phenyl)-6-phenyl-1.3,5-hexatrie
ne (TMA-DPH). The membrane surface accessibility was evaluated by fluoresce
nce quenching of 2-(9-anthroyloxy) stearic acid (2-AS). Whatever the ionic
strength tested, the polysaccharide presence notably enhances the membrane
fluidity below the T-m. This sign of an interaction in the polar level of t
he membrane is more marked at low NaCl concentration. In contrast, the lipo
somes bilayer accessibility is drastically lowered when increasing the ioni
c strength. This is induced by macromolecular chain adsorption on the lipos
ome surface, enhanced by the polysaccharide chain association. An ionic str
ength enhancement induces a conformational modification of the polysacchari
de chains which modifies their ability to interact with the bilayer. Copyri
ght (C) 2001 John Wiley & Sons, Ltd.