Thalia Mills
Department of Physics,
Carnegie Mellon University
Abstract:
Coexistence of liquid-disordered (Ld) and liquid-ordered (Lo) domains in model membranes
is thought to be related to cell membrane "rafts", cholesterol-rich lipid heterogeneities
which provide platforms for protein sorting. In unoriented wide angle x-ray scattering
(WAXS) data, scattering from the Ld and Lo phases looks similar, whereas in WAXS patterns
from oriented samples, these phases are easily distinguishable because of the differences
in their chain orientational order. A simple analytical model to relate the WAXS data to
the chain orientational distribution was used to obtain an average orientational order
parameter, Sxray. In addition to quantifying the effect of cholesterol on Sxray,
oriented WAXS data was used to identify Ld/Lo phase coexistence in lipid mixtures where
other techniques such as NMR and fluorescence microscopy previously indicated phase coexistence.
In addition to being probe free, this new x-ray method for detecting Ld and Lo domains is
advantageous because of the sensitivity of WAXS to very short time and length scales.
