Hemifusion activity of a chimeric influenza virus hemagglutinin with a putative fusion peptide from hepatitis B virus

Entry of enveloped viruses is often mediated by an aminoterminal hydrophobi c fusion peptide of a viral surface protein. The S domain of the hepatitis B virus surface protein contains a putative fusion peptide at position 7-18 , but no systems are available to study its function directly. We tested th e functionality of this peptide and a related peptide from another hepadnav irus in the context of the well-characterized influenza virus hemagglutinin H7 using gene mutation. The chimeric hemagglutinins could be expressed sta bly in CV 1 cells and were transported to the cell surface. The chimeras we re incompletely cleaved by cellular proteases but cleavage could be complet ed by trypsin treatment of the cells. The chimeras did not differ in recept or binding, i.e. erythrocyte binding. Hemifusion and fusion pore formation were detected with membrane or cytosolic fluorescent dye-labeled erythrocyt es as target structures of the hemagglutinin. Five of six different chimera s mediated hemifusion in 20-54% of the hemagglutinin-expressing cells, comp lete fusion and syncytium formation was not observed. The data suggest that the sequence 7-18 of the hepatitis B S domain may indeed initiate the firs t step of viral entry, i.e. hemifusion. (C) 2000 Elsevier Science B.V. All rights reserved.