Plasma
membranes are assumed to be highly compartmentalized, which
is believed to be important for the membrane protein functionality.
The liquid ordered-disordered phase segregation in the membranes results
in nanoscale liquid-ordered assemblieslipid rafts. Double
electron–electron resonance spectroscopy (DEER, also known
as PELDOR) is sensitive to spin–spin dipolar interactions between
spin labels at the nanoscale range of distances. Here, DEER is applied
to spin-labeled cholestane, 3β-doxyl-5α-cholestane (DChl),
diluted in bilayers composed of an equimolar mixture of dioleoyl-glycero-phosphocholine
(DOPC) and dipalmitoyl-glycero-phosphocholine (DPPC) phospholipids,
with cholesterol (Chol) added. The DEER data allowed us to detect
clustering of the DChl molecules. Their lateral distribution in the
clusters in the absence of Chol was found to be random, while in the
presence of Chol it became quasi-regular. DEER time traces are fairly
well simulated within a simple square superlattice model. For the
20 mol % Chol content, for which at physiological temperatures, the
lipid rafts are formed, the found superlattice parameter was 3.7 nm.
Assuming that lipid rafts are captioned upon shock freezing at the
temperature of investigation (80 K), the found regularity of DChl
lateral distribution was interpreted by raft substructuring, with
the DChl molecules embedded between the substructures.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.