Molecular events during the interaction of envelopes of myxo- and RNA-tumor viruses with cell membranes. A 270 MHz 1H nuclear magnetic resonance study

The nuclear magnetic resonance (NMR) spectra of chick embryo cells have been analyzed after exposure to Newcastle disease virus (NDV). Virions that contained the envelope glycoproteins in the cleaved form and, thus, had full biological activity have been compared to virions that had reduced infectivity due to the presence of uncleaved glycoprotein F. After exposure to infectious virus, drastic changes occurred in the signals assigned to choline and the hydrocarbon chains of fatty acids. These observations are interpreted to demonstrate alteration of the fluid lipid bilayer structure of the cell membranes. This is compatible with the concept of membrane fusion as a penetration mechanism for NDV. Virus containing uncleaved F glycoprotein did not alter the NMR spectra. This indicates that infection is blocked at the stage of penetration.Similar, though less pronounced, differences have been observed when the effects of highly infectious influenza virus containing the hemagglutinin in the cleaved form were compared to the effects of virus which had a lower infectivity due to the presence of uncleaved hemagglutinin. Thus, it appears that the hemagglutinin of influenza virus is involved in penetration and that cleavage is necessary for this function.Alterations of the NMR spectra of the membrane lipids have also been observed when susceptible chick embryo cells (C/E) were infected with Rous sarcoma virus of subgroup B. Such alterations did not occur when nonsusceptible cells (C/B) were used. Thus, infection appears to be blocked again at the stage of penetration.