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Kinetic and Thermodynamic Analysis of Cholesterol Transfer between Phospholipid Vesicles and Nanodiscs
We investigated interparticle transfer
of cholesterol (Chol) between
large unilamellar vesicles (LUVs) and phospholipid bilayer nanodiscs.
The Chol transfer rate from LUVs to nanodiscs was decreased by an
increase in the Chol content or incorporation of sphingomyelin in
donor phosphatidylcholine/Chol LUVs but was not influenced by the
lipid composition of acceptor particles. These results suggest that
Chol dissociation from the lipid bilayer into aqueous phase is the
rate-limiting step of the transfer and that the process depends on
the fluidity of the donor membranes. The Chol dissociation rate from
nanodiscs was faster than that from LUVs with similar lipid composition.
Chol preferably partitioned to LUVs rather than nanodiscs, which is
consistent with the faster dissociation rate from nanodiscs. The activation
energy of Chol dissociation from nanodiscs was 1.7 kJ/mol lower than
that from LUV, which was brought by increased (less negative) activation
entropy and enthalpy. In addition, fluorescence lifetime and anisotropy
data revealed that the lipid bilayer of nanodiscs is more tightly
packed than that of LUVs. These results suggest that the tighter lipid
packing in nanodiscs destabilizes the Chol-containing bilayer by reducing
the entropy, which facilitates Chol dissociation