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Professor: Mary L. Kraft
University of Illinois
600 S. Mathews Ave,. MC-712
Urbana, IL 61801
phone: 217-333-2228
fax: 217-333-5052
Influenza Infection and Cell Membrane Organization
Influenza and HIV are global tragedies, killing millions of people every year. The virulence of HIV, influenza, and other enveloped viruses depend on their ability to manipulate the cell’s plasma membrane. The plasma membrane is a selectively permeable barrier that separates the cell from its external environment. Virus particles must pass through the cell membrane to start infection, and new particles also assemble and bud from the cell membrane. Hundreds of different kinds of lipids make up the plasma membrane, but depleting the cells of just a few lipid types- namely cholesterol and sphingolipids, often results in the formation of defective virus particles. The site of virus particle assembly is believed to be enriched with cholesterol and sphingolipids, but no one really knows the precise lipid composition at the site of virus budding, or why these components are required because no one can directly measure the lipid composition within tiny domains in the cell membrane.
The Kraft laboratory uses a nanoscale imaging secondary ion mass spectrometry approach to directly map how different lipids are distributed in cell membranes with 50 – 100 lateral resolution. This technique is called multiple isotope imaging mass spectrometry (MIMS) and it reveals the elemental and isotopic composition at the sample’s surface. Briefly, the technique works by bombarding the surface with a tightly focused cesium ion beam. This beam fragments the molecules on the surface of the sample into atomic and diatomic species. A fraction of these species are ionized, and the “secondary ions” ejected at each beam position are collected and analyzed according to their mass. This beam is scanned across the sample, and a map of the sample’s elemental and isotopic composition is created. By metabolically incorporating a distinct stable isotope into each cell membrane species of interest within influenza-infected cells (i.e., cholesterol, sphingolipids, unsaturated lipids, and influenza proteins) we can use the isotopically enriched secondary ions that are specific to each labeled component to create an image of how they are distributed in the cell’s plasma membrane with 50 – 100 nm lateral resolution.
This approach to “image” the lipid composition in the cell membrane is being used to determine how intracellular transport and cellular metabolism contributes to cell membrane organization, and how the influenza virus manipulates these mechanisms to promote its replication. This information can lead to the development of better anti-influenza therapeutics.