Called sphingolipids (sfing-go-lipids), these molecules are thought to associate with cholesterol to form small domains about 200 nanometers across. The direct imaging method revealed that sphingolipids do form domains, but not in the way the researchers expected.
The domains were much bigger than results from prior experiments. The 200-nanometer domains clustered together to form much larger, micrometer-sized patches of sphingolipids in the membrane.
"We were amazed when we saw the first images of the patches of sphingolipids across the cell surface," said Peter Weber, who directed the team at Lawrence Livermore. "At the start, we weren't sure if our imaging mass spectrometry method would be sensitive enough to detect the labeled lipids, let alone what we would see."
When the researchers looked at cells that were low on cholesterol thought to play a key role in lipid aggregation they were surprised to find that the lipids still formed domains. But disruption to the cell's structural scaffold seemed to dissolve the lipid clusters.
"We found that the presence of domains was somewhat affected by cholesterol but was more affected by the cytoskeleton the protein network underneath the membrane," Kraft said. "The central issue is that the data is suggesting that the mechanism that's responsible for these domains is much more complicated than initially expected."
In addition, the new study found that sphingolipid domains were incompletely associated with a marker protein that researchers have long assumed lived where sphingolipids congregated. This means that data collected with imaging techniques that target this protein are not as accurate in representing sphingolipid distribution as previously thought.
"Our data is showing that if you want to know wher
|Contact: Anne Stark|
DOE/Lawrence Livermore National Laboratory