New Fluorescent Technique Allows Quantitative Measurement of Cell Membrane Lipids

A recent paper described the development of a method for the in situ quantification of cell membrane lipids, which are important signaling elements that have been linked to certain disease states, inflammation, and the immune response system.

The current study is among the first to describe a quantitative method for measuring lipid concentration in the membrane of a living cell. To accomplish this task investigators at the University of Illinois (Chicago, USA) used a new chemical method to label proteins with an environmentally sensitive fluorophore. A prototype sensor for the lipid phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2) - a key signaling lipid in diverse cellular processes - was generated by covalently attaching a single 2-dimethylamino-6-acyl-naphthalene group to the N-terminal alpha-helix of the engineered epsin1 ENTH domain, a protein that selectively binds PtdIns(4,5)P2.

Results reported in the October 9, 2011, online edition of the journal Nature Chemistry revealed that tracking the signal generated by binding of the fluorescent protein to this key signaling lipid allowed robust and sensitive in situ quantitative imaging in mammalian cells that provided new insight into the dynamics and fluctuation of the lipid within the microenvironment of the cell membrane.

“Lipid molecules on cell membranes can act as switches that turn on or off protein-protein interactions affecting all cellular processes, including those associated with disease," said senior author Dr. Wonhwa Cho, professor of chemistry at the University of Illinois. “While the exact mechanism is still unknown, our hypothesis is that lipid molecules serve sort of like a sliding switch. It is not just the presence of lipid, but the number of lipid molecules that are important for turning on and off biological activity.”

“We had to engineer the protein in such a way to make it very stable, behave well, and specifically recognize a particular lipid,” said Dr. Cho. “We would like to be able to measure multiple lipids, simultaneously. It would give us a snapshot of all the processes being regulated by the different lipids inside a cell.”

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