title: Lipid-anchored influenza hemagglutinin promotes hemifusion, not complete fusion.
abstract: It has been proposed that membrane fusion events such as virus-cell fusion proceed through a hemifusion intermediate, a state where lipids but not contents of the fusing compartments mix. We engineered the influenza hemagglutinin (HA) such that it would be anchored in membranes via a glycosylphosphatidylinositol (GPI) tail. GPI-anchored HA forms a trimer that can bind red blood cells (RBCs) and change conformation under fusion-inducing conditions. Using RBCs labeled with fluorescent lipid or fluorescent soluble content probes, we found that GPI-anchored HA mediated lipid mixing with similar time course and efficiency as wt-HA, yet did not mediate transfer of soluble contents. Hence, GPI-anchored HA appears to initiate, but not complete, a fusion reaction. We interpret our results as evidence for uncoupling a physiological fusion reaction, for trapping a hemifusion intermediate, and for assigning a role to a transmembrane domain in a fusion event.
authors.affiliation: Department of Pharmacology, University of California, San Francisco 94143-0450.
authors.forename: G W
authors.initials: GW
authors.lastname: Kemble
authors.forename: T
authors.initials: T
authors.lastname: Danieli
authors.forename: J M
authors.initials: JM
authors.lastname: White
mesh_terms: D001483:Base Sequence; D017931:DNA Primers / Q000737:chemistry; D017261:Glycosylphosphatidylinositols; D006389:Hemagglutinins, Viral / Q000737:chemistry*; D066298:In Vitro Techniques; D008561:Membrane Fusion; D008563:Membrane Lipids / Q000737:chemistry; D008969:Molecular Sequence Data; D009975:Orthomyxoviridae
chemical_list: D017931:DNA Primers; D017261:Glycosylphosphatidylinositols; D006389:Hemagglutinins, Viral; D008563:Membrane Lipids