The influenza haemagglutinin-induced fusion cascade: effects of target membrane permeability changes

To define the stages in influenza haemagglutinin (HA)-mediated fusion the k inetics of fusion between cell pairs consisting of single influenza HA-expr essing cells and single erythrocytes (RBC) which had been labelled with bot h a fluorescent lipid (Dil) in the membrane and a fluorescent solute (calce in) in the aqueous space have been monitored. It is shown that release of s olute from the target cell occurs, following the formation of the hemi-fusi on diaphragm. These results are discussed in terms of a model in which fusi on peptide insertion into the target membrane induces lipid stalks, which r esults in the formation of a hemifusion diaphragm and a fusion pore. Bilaye r expansion due to overproduction of these stalks can give rise to collater al damage of target membranes.