Membrane Fusion of HVJ Envelope and Red Blood Cell Membrane

The initial stage of the interaction between HVJ virions and cells is reviewed focusing on the membrane fusion phenomenon of JVJ envelope and cell membrane.The viral protein responsible for the membrane fusion has been identified as the F glycoprotein which forms F spikes on the surface of the virion. The fusing activity of the F spike is activated by a post-translational cleavage of the F glycoprotein. The virion has a second kind of glycoprotein, HANA, which forms HANA spikes. The HANA spike possesses tow opposite activities; one is hemagglutinating activity which reflects the ability of the virus to attach the receptor, and the other is neuraminidase activity by which the virus destroys the receptor.The initial interaction between HVJ virious and cells has been intensively studied using a simplified system consisting of HVJ and red blood cells. The viral envelope comes into close contact with the celle membrane by the binding of several hundred HANA spikes on the virion envelope with the receptors on the cell membrane. Subsequently, morphological dissolution of both the viral envelope and cell membrane occurs in some parts of the region of virus-cell contact. This dissolution has been attributed to the reaction of the F spikes with the cell membrane. Immediate fusion of the virus envelope with the cell membrane then takes place. Thus the dissolved area is sealed with the virus envelope and no leakage of hemoglobin or K+ is detected throughout these virus-cell interactions. However, if viral envelope has been made permeable by freezing and thawing, immune-virolysis or heat, ion leakage occurs after envelopemembrane fusion and hemolysis follows. The F and HANA spikes integrated into cell membrane by virus-cell fusion retain their activities and can cause the cell to fuse with the other cells. Subsequently virus-cell fusion and cell-cell fusion cease as a result of the destruction of cell receptors by the neuraminidase activity of the HANA spikes.