KINETICS OF FUSION WITH CELLS OF RECONSTITUTED SENDAI VIRUS ENVELOPESLACKING HEMAGGLUTININ-NEURAMINIDASE

The fusion potential of reconstituted Sendai virus envelopes containin g only the F protein (F-virosomes) has been assessed. F-virosomes and F,HN-virosomes were prepared by solubilization of the intact virus in Triton X-100 followed by its removal using SM-2 biobeads. Viral envelo pes containing HN whose disulphide bonds were irreversibly reduced (HN red) were also prepared by treating the envelopes with dithiothreitol followed by dialysis. Both F-virosomes and F,HNred-virosomes hemolysed red blood cells in the presence of wheat germ agglutinin. The rates a nd extent of hemolysis induced by these virosomes were, however, signi ficantly lower than that induced by F,HN-virosomes. Using a fluorescen ce probe based membrane mixing fusion assay, F- and F,HNred-virosomes were found to fuse with cultured HeLa cells in the presence of wheat-g erm agglutinin. A direct comparison of the fusion activity of F,HN-vir osomes and F-virosomes was made by using desialylated HepG2 cells as t arget containing the asialoglycoprotein. receptor (ASGP-R) that binds to a terminal beta-galactose moiety of F protein. A 2- to 3-fold enhan cement in the fusion rate when HN was included in the viral envelope w as observed. Based on the kinetic data, a model for fusion of paramyxo -virosomes with HepG2 cells is proposed.