Lipid-protein interactions in enveloped viruses

Structural changes in BHK cell plasma membrane caused by the binding of vesicular stomatitis virus

Spin label electron spin resonance techniques using a nitroxide derivative of stearic acid were used to detect changes in plasma membrane structure caused by the binding of vesicular stomatitis virus (VSV) to cell plasma membranes of intact BHK-21 cells. The results indicate that binding of VSV to cell surface receptors causes an increase in the observed rigidity of the plasma membrane lipid bilayer. This change in membrane structure, which appears to be caused by the cross-linking of receptors in the plane of the plasma membrane, could be prevented by treating the cells with colchicine before addition of virus and could be reversed by treating the cells with colchicine after addition of virus. Cells treated with a monovalent, water-soluble derivative of VSV G-protein (Gs) did not show an increase in plasma membrane bilayer rigidity. However, addition of anti-VSV G-protein immunoglobulin G to cells pretreated with G8 caused an increase in plasma membrane bilayer rigidity. This increased rigidity could also be reversed by the addition of colchicine. Fluorescence microscopy was used to determine the distribution of fluorescein-labeled VSV particles on the cell surface after addition of virus. Approximately 30 min after addition of virus, discrete areas on the cell surface showed fluorescent staining, which coalesced to apical regions of the cell after approximately 40 min.

Beta-interferon-induced time-dependent changes in the plasma membrane lipid bilayer of cultured cells

The time-dependent interferon-induced structural changes in the plasma membrane lipid bilayer have been investigated in cultured cells using spin label electron spin resonance techniques. Treatment of human HeLa-S3 cells in suspension culture with human beta 1 interferon (640 u/ml) for as short a time as 30 min causes an increase in the rigidity of the plasma membrane lipid bilayer (Landsberger, Pfeffer and Tamm, in preparation). The plasma membrane rigidity of interferon-treated cells returns to the level of control cells within 3 to 5 hr, but by 24 hr after beginning of treatment, the rigidity of the plasma membrane is increased again and remains so for at least 2 days. Mouse beta interferon causes both an early (Landsberger, Pfeffer and Tamm, in preparation) and a late increase in membrane rigidity in homologous mouse L-929 cells, but not in heterologous HeLa-S3 cells. Thus, the interferon-induced perturbation of membrane structure is species specific. The late increase in membrane rigidity may have a different underlying mechanism from that of the early increase. While the early and transient change probably is related to signal generation and transmission, the later and persistent change may be an aspect of the phenotype and interferon-treated cells and may reflect changes in the plasma membrane-cytoskeletal complex.