November 2, 2010

The Scientist: Susan Daniel

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The leaves are falling, the temperature is dropping, and the days are becoming shorter. Flu season has arrived in Ithaca.

The influenza virus – which causes the flu – is not generally life-threatening. However, last year the H1N1 virus alerted the world to the fact that severe flu symptoms may cause death. The World Health Organization and the U.S. Center for Disease Control declared the outbreak to be a pandemic.

Although scientists knew of H1N1 before last year, the outbreak was caused by a new strain of the virus. This strain was not dramatically potent but could be transmitted very quickly and easily.

Prof. Susan Daniel, chemical and biomolecular engineering, researches cell membrane mimics and novel devices for the study of transmembrane species interactions. Such interactions are important for the study of how viruses affect host cells and subsequently, for the study of vaccines.

“Vaccines are developed by guessing ahead of time what virus is going to make a big impact. However, sometimes … there are stronger mutants,” Daniel said.

Daniel and her group developed a tool to identify how different factors of a strain relate to its effects on the host cell. A virus’ infection of host cells is a multi-step process that resembles an invasion. Viruses send their troops (genetic material, like RNA) to breach the city walls (cellular membranes) and set up camp.  Inside the conquered city, the virus trains new soldiers (new viruses).

Overall, the infection includes viral fusion, transmitting genetic material across the cell membrane and initiating the replication of more viruses. Using a single-particle microscopy technique, Daniel can observe each of these processes for individual viruses in real time.

Daniel puts a membrane bilayer on a planar glass microscope slide and attaches dye-labeled viruses to the membrane. A total internal fluorescence microscope (TIRF) is used to focus on the plane, upon which the viruses appear like bright stars in a black sky. The dye gets brighter when the viruses partially fuse to the membrane. A different dye gets dimmer when the viruses completely fuse.

This set-up is very different from other virus fusion assays, which typically just mix dye-labeled viruses and membranes. In these assays, scientists simply observe the solution getting brighter as the virus fuses with the membrane, and they must guess, with some uncertainty, about the interactions of the virus with the membrane.

Daniel, on the other hand, can visually confirm a virus fusion event and even distinguish between the partial fusion and the complete fusion of a virus.

Virus fusion is triggered by acidification of the environment. Typically, fusion occurs within milliseconds, and a slow acidification may limit the accurate observation of the kinetics. Recently, Daniel developed a method to reduce the time-resolution of this step to meet the kinetics of the fusion. Her assay provides the optimum set-up both spatially and temporally to study the fusion process.

Daniel studies the effects of different viral mutations.  She tries to identify which cells of the body are most susceptible to certain mutations.

“Our tool will help understand how mutation impacts how viruses bind and fuse. Furthermore, we hope that this tool could be used when people screen for what might be the most important virus in that year (to develop vaccines),” Daniel said.

Original Author: Eugene Choi