posted on 2016-12-07, 00:00authored byFrank
R. Moss, Steven G. Boxer
The
lateral organization of biological membranes is thought to
take place on the nanometer length scale. However, this length scale
and the dynamic nature of small lipid and protein domains have made
characterization of such organization in biological membranes and
model systems difficult. Here we introduce a new method for measuring
the colocalization of lipids in monolayers and bilayers using stable
isotope labeling. We take advantage of a process that occurs in dynamic
SIMS called atomic recombination, in which atoms on different molecules
combine to form diatomic ions that are detected with a NanoSIMS instrument.
This process is highly sensitive to the distance between molecules.
By measuring the efficiency of the formation of 13C15N– ions from 13C and 15N atoms on different lipid molecules, we measure variations in the
lateral organization of bilayers even though these heterogeneities
occur on a length scale of only a few nm, well below the diameter
of the primary ion beam of the NanoSIMS instrument or even the best
super-resolution fluorescence methods. Using this technique, we provide
direct evidence for nanoscale phase separation in a model membrane,
which may provide a better model for the organization of biological
membranes than lipid mixtures with microscale phase separation. We
expect this technique to be broadly applicable to any assembly where
very short scale proximity is of interest or unknown, both in chemical
and biological systems.