Monday 17.05.

8:00 PDT -  11:00 EDT - 15:00 UTC

16:00 BST - 17:00 CEST - 18:00 IDT

Brian Dyer

Department of Chemistry, Emory University

Protein mediated membrane fusion studied by time resolved spectroscopy

The molecular basis of transmission and pathogenesis of the influenza virus is incompletely understood. Key early steps in the viral infection process involve acidification of the viral lumen by the M2 proton channel and membrane fusion mediated by hemagglutinin. These coordinated events are triggered by the low pH of the endosome and together facilitate release of the viral contents into the cytosol of the host cell. M2 is a highly selective and unidirectional proton channel that is activated at low pH, switching on proton conductance and acidifying the viral lumen to enable release of the viral ribonucleoproteins. While the structure of M2 has been determined at neutral and low pH, the dynamics that activate proton conductance are not known. The second essential step of infection is the formation of a fusion pore, mediated by the viral coat protein hemagglutinin (HA). Hemagglutinin has served as an archetype for understanding the general mechanism of membrane fusion and it is also an important target for antiviral drug development. HA is postulated to undergo an astounding series of refolding reactions triggered by lowered pH. The proposed spring-loaded mechanism of HA mediated membrane fusion has been inferred from equilibrium structures of pre- and post-fusion states, despite the highly dynamic nature of its pH dependent structure. As a consequence, the molecular details of HA mediated membrane fusion are not known, particularly with respect to the protein-membrane interactions. We have explored the molecular mechanism of HA mediated membrane fusion and M2 mediated proton transport that enable influenza virus infection, using time-resolved infrared and fluorescence spectroscopies of these proteins reconstituted in lipid vesicles. We have characterized the functional dynamics of HA and M2 induced by low pH using the laser pH-jump as a trigger and time resolved spectroscopy to map the structural dynamics.