Formation of Inverse Topology Lyotropic Phases in Dioleoylphosphatidylcholine/Oleic Acid and Dioleoylphosphatidylethanolamine/Oleic Acid Binary Mixtures

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Abstract

The addition of saturated fatty acids (FA) to
phosphatidylcholine lipids (PC) that have saturated acyl chains
has been shown to promote the formation of lyotropic liquidcrystalline
phases with negative mean curvature. PC/FA
mixtures may exhibit inverse bicontinuous cubic phases
(Im3m, Pn3m) or inverse topology hexagonal phases (HII),
depending on the length of the acyl chains/fatty acid. Here we
report a detailed study of the phase behavior of binary
mixtures of dioleoylphosphatidylcholine (DOPC)/oleic acid
(OA) and dioleoylphosphatidylethanolamine (DOPE)/oleic
acid at limiting hydration, constructed using small-angle X-ray
diffraction (SAXD) data. The phase diagrams of both systems
show a succession of phases with increasing negative mean
curvature with increasing OA content. At high OA concentrations, we have observed the occurrence of an inverse micellar Fd3m
phase in both systems. Hitherto, this phase had not been reported for phosphatidylethanolamine/fatty acid mixtures, and as such
it highlights an additional route through which fatty acids may increase the propensity of bilayer lipid membranes to curve. We
also propose a method that uses the temperature dependence of the lattice parameters of the HII phases to estimate the
spontaneous radii of curvature (R0) of the binary mixtures and of the component lipids. Using this method, we calculated the R0
values of the complexes comprising one phospholipid molecule and two fatty acid molecules, which have been postulated to drive
the formation of inverse phases in PL/FA mixtures. These are −1.8 nm (±0.4 nm) for DOPC(OA)2 and −1.1 nm (±0.1 nm) for
DOPE(OA)2. R0 values estimated in this way allow the quantification of the contribution that different lipid species make to
membrane curvature elastic properties and hence of their effect on the function of membrane-bound proteins.

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Forskningsområden

Ämnesklassifikation (UKÄ) – OBLIGATORISK

  • Fysik
  • Naturvetenskap
Originalspråkengelska
Sidor (från-till)3337-3344
TidskriftLangmuir
Volym30
Utgivningsnummer12
StatusPublished - 2014
PublikationskategoriForskning
Peer review utfördJa