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Solving a cell membrane mystery

Date:
April 24, 2017
Source:
Institute for Integrated Cell-Material Sciences at Kyoto University
Summary:
Scientists have developed new fluorescent probes that prove the existence of cell membrane structures called ‘lipid rafts’, allowing researchers to study how toxins and viruses invade cells.
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Top: Typical image sequences (every 33 milliseconds) of a raft domain undergoing signaling (green) and a sphingomyelin analog (red). The sphingomyelin analog molecule was associated with a signaling raft domain from frame 4 to 9 (orange arrows). Bottom: Schematic model showing the transient recruitment of sphingomyelins to various raft domains in the time scale of 10 to 50 milliseconds. The signaling raft itself was stable for up to several tens of minutes, working as a stable signaling platform.
Credit: Image courtesy of Institute for Integrated Cell-Material Sciences at Kyoto University

Scientists have developed new fluorescent probes that prove the existence of cell membrane structures called 'lipid rafts', allowing researchers to study how toxins and viruses invade cells.

Scientists from Japan, India and the US have observed lipid rafts in live cells for the first time. These rafts are active sections of the cell membrane responsible for signal transduction as well as the entry of toxins into cells.

The existence of lipid rafts had been assumed for over 25 years, but had never been observed in living cells.

To solve this enigma, the team focused on the behaviours of gangliosides: lipid molecules that were thought to play a central role in forming lipid rafts.

However, scientists only vaguely understood how gangliosides work because, until now, they lacked probes that could accurately track the lipids' movements. Previous ganglioside analogues (in which florescent dye is attached) did not partition into rafts, even in artificial model systems. Researchers suspect the dyes were hydrophobic and altered how the ganglioside interacted with the cell membrane.

So, instead of just attaching a fluorescent marker to a ganglioside, the team chemically synthesized four whole gangliosides with fluorescent markers attached at specific locations. They determined which ones accurately mimicked real gangliosides, partitioning into rafts in the model system.

When the team inserted the new analogues into a living cell and used high-definition, single fluorescent-molecule imaging, they were finally able to directly document the actions of specific gangliosides in a living cell for the first time.

The researchers observed how gangliosides form lipid rafts with cholesterol and a receptor protein called CD59. It turns out these molecules interact transiently for only tens of milliseconds to form a lipid raft, and then quickly move to form a new raft. That's why no one could observe the rafts in real cells before.

"Our findings established the concept of dynamic [lipid rafts]: their constituent molecules assemble to form [rafts], do their jobs [quickly] and then move away for the next assembly to perform the next task," says Dr Kenichi Suzuki of Kyoto University's Institute for Integrated Cell-Material Sciences and the paper's co-author.


Story Source:

Materials provided by Institute for Integrated Cell-Material Sciences at Kyoto University. Note: Content may be edited for style and length.


Journal Reference:

  1. Masanao Kinoshita, Kenichi G.N. Suzuki, Nobuaki Matsumori, Misa Takada, Hikaru Ano, Kenichi Morigaki, Mitsuhiro Abe, Asami Makino, Toshihide Kobayashi, Koichiro M. Hirosawa, Takahiro K. Fujiwara, Akihiro Kusumi, Michio Murata. Raft-based sphingomyelin interactions revealed by new fluorescent sphingomyelin analogs. The Journal of Cell Biology, 2017; 216 (4): 1183 DOI: 10.1083/jcb.201607086

Cite This Page:

Institute for Integrated Cell-Material Sciences at Kyoto University. "Solving a cell membrane mystery." ScienceDaily. ScienceDaily, 24 April 2017. <www.sciencedaily.com/releases/2017/04/170424172255.htm>.
Institute for Integrated Cell-Material Sciences at Kyoto University. (2017, April 24). Solving a cell membrane mystery. ScienceDaily. Retrieved May 22, 2017 from www.sciencedaily.com/releases/2017/04/170424172255.htm
Institute for Integrated Cell-Material Sciences at Kyoto University. "Solving a cell membrane mystery." ScienceDaily. www.sciencedaily.com/releases/2017/04/170424172255.htm (accessed May 22, 2017).

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