DIVALENT CATION-DEPENDENT INTERACTION OF SULFATED POLYSACCHARIDES WITH PHOSPHATIDYLCHOLINE AND MIXED PHOSPHATIDYLCHOLINE PHOSPHATIDYLGLYCEROL LIPOSOMES
G. Steffan et al., DIVALENT CATION-DEPENDENT INTERACTION OF SULFATED POLYSACCHARIDES WITH PHOSPHATIDYLCHOLINE AND MIXED PHOSPHATIDYLCHOLINE PHOSPHATIDYLGLYCEROL LIPOSOMES, Chemistry and physics of lipids, 74(2), 1994, pp. 141-150
The Ca2+-dependent interaction of various polyanionic polysaccharides
(chondroitin sulfate, heparin, dextran sulfate, beta-cyclodextrin sulf
ate, hyaluronic acid and carboxymethyldextran) with multilamellar dimy
ristoyl phosphatidylcholine (DMPC) liposomes was investigated by calor
imetric and fluorescence spectroscopic measurements. It was found that
an observed polysaccharide-induced phospholipid phase separation depe
nds on the density of the sulfate groups along the polysaccharide chai
n independent of the presence of additional carboxyl groups. The phase
separation resulting from the drastic dehydration of the covered memb
rane regions is monitored by the upward shift of the lipid phase trans
ition and by the blue shift of the emission spectrum of a headgroup-da
nsylated phosphatidylethanolamine (DPE). This shift is only observable
if the required polysaccharide chain length contains at least three g
lycosyl units. The Ca2+-mediated interaction of dextran sulfate with v
arious phosphatidylcholines, differing in their compressibility, showe
d the maximal difference between the phase transition temperatures of
the lipid phase covered by the polysaccharide and the uneffected lipid
domains for dielaidinoyl phosphatidylcholine (DEPC), the most compres
sible phospholipid investigated here. Mixed negatively charged DMPC/di
myristoyl phosphatidylglycerol (DMPG) liposomes were found to compete
with the likewise negatively charged dextran sulfate for the binding o
f Ca2+. At excess Ca2+ concentrations, the binding of the polysacchari
de was strengthened, compared to pure DMPC liposomes. The monovalent c
ation sodium, was able to inhibit the interaction between the membrane
surface and dextran sulfate. Various divalent cations were found to m
ediate the interaction, depending on their ionic radii and electron co
nfiguration. Within the second group of the periodic system Ca2+ is th
e most effective ion. However, within the horizontal forth period the
ability to bind sulfated dextran to membrane surfaces decreases from C
a2+ to Ni2+, but then increases again if Cu2+ or Zn2+ was used as the
mediating ion.