How the flu virus builds a better mousetrap

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BOSTON (June 28, 2018)—For the first time, scientists have directly visualized in real-time structural changes in the surface protein of the influenza virus that may help the virus to fuse with and enter target cells before hijacking their functions. Researchers at Tufts University School of Medicine found that single molecules of  the protein hemagglutinin (HA) that reside on the surface of the virus unfold to stretch toward target cells, then refold and try again 5 to 10 times per second. The discovery shows the flu virus to be more dynamic than previously thought and may help efforts to develop more effective vaccines and better understand other viruses such as Ebola, HIV, and SARS. The research appears in the journal Cell online June 28 and in print August 9.For decades, influenza has served as the study model for a large class of viruses that enter cells by a common mechanism: An envelope protein on the surface of these viruses must attach the virus to the cell membrane, and then fuse the virus and the cell. Fusion allows release of the virus contents into the cell, so it can take over the cell’s internal functions and replicate. Influenza’s envelope protein, HA, has long been a template for fusion mechanisms in other viruses.
“Envelope proteins have been described as old-fashioned mousetraps, set in a static, spring-loaded state, waiting to be triggered by interaction with a target cell,” said the study’s senior author, James Munro, PhD., assistant professor of molecular biology and microbiology at Tufts School of Medicine who also teaches at the Sackler School of Graduate Biomedical Sciences at Tufts. “Once triggered, they undergo a dramatic change in their three-dimensional structure, enabling fusion and entry into the target. However, despite some hints in previous research, this process hadn’t been directly observed, and it was widely thought that each protein molecule on the surface …

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