The glycoprotein hemagglutinin (HA) of influenza virus is the driving force for virus budding and it is supposed that its concentration in membrane-rafts, microdomains of the plasma membrane enriched in cholesterol and sphingolipids, is a prerequisite for that function. We are interested in characterization of the interaction of HA with lipid domains, in particular membrane-rafts using essentially biophysical methods, both in living cells and in model membranes. We have created fluorescent and functional HA-constructs that cluster inside cells with established markers for rafts, as revealed by fluorescence resonance energy transfer (FLIM-FRET). Clustering was significantly reduced when cholesterol which is a major building block of rafts was depleted and when the raft-targeting signals of HA, palmitoylation sites and hydrophobic amino acids in the transmembrane region, were removed. Lipid domain specific recruitment was also depend on the conformation of the HA ectodomain. Furthermore, we have shown that Giant Unilamellar Vesicles (GUVs) can be used to create, visualize and characterize lipid-domains and to study partitioning of HA and of its transmembrane region into liquid-ordered or liquid-disordered domains.

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