title: Autocatalytic activation of influenza hemagglutinin.
abstract: Enveloped viruses contain surface proteins that mediate fusion between the viral and target cell membranes following an activating stimulus. Acidic pH induces the influenza virus fusion protein hemagglutinin (HA) via irreversible refolding of a trimeric conformational state leading to exposure of hydrophobic fusion peptides on each trimer subunit. Herein, we show that cells expressing fowl plague virus HA demonstrate discrete switching behavior with respect to the HA conformational change. Partially activated states do not exist at the scale of the cell, activation of HA leads to aggregation of cell surface trimers, and newly synthesized HA refold spontaneously in the presence of previously activated HA. These observations imply a feedback mechanism involving self-catalyzed refolding of HA and thus suggest a mechanism similar to the autocatalytic refolding and aggregation of prions.
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Pennsylvania, 220 South 33rd Street, Philadelphia, PA 19104, USA.
authors.forename: Jeong H
authors.initials: JH
authors.lastname: Lee
authors.forename: Mark
authors.initials: M
authors.lastname: Goulian
authors.forename: Eric T
authors.initials: ET
authors.lastname: Boder
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002384:Catalysis; D002462:Cell Membrane / Q000378:metabolism; D004789:Enzyme Activation; D006389:Hemagglutinins, Viral / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D009980:Influenza A virus / Q000378:metabolism*; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D011487:Protein Conformation; D017510:Protein Folding; D014760:Viral Fusion Proteins / Q000378:metabolism*
chemical_list: D006389:Hemagglutinins, Viral; D014760:Viral Fusion Proteins