INFLUENCE OF THE SPECTRIN NETWORK ON FUSION OF INFLUENZA-VIRUS WITH RED-BLOOD-CELLS

We examined the influence of the physical state of the membrane skelet on on low pH fusion of influenza virus A/PR 8/34 with intact human red blood cells. Spectrin, the major component of the skeleton, is known to become denaturated at 50 degrees C. After heat treatment of erythro cytes at 50 degrees C we observed an enhanced kinetics of fusion monit ored spectrofluorometrically by the octadecylrhodamine fluorescence de quenching assay, while the extent of fusion was not affected. The acce lerated fusion of influenza virus after preincubation of red blood cel ls at 50 degrees C is not mediated by alterations of the lipid phase o f the target. From ESR measurements using spin-labelled phospholipids we conclude that heat-induced alterations of the spectrin network did not affect either the phospholipid asymmetry or the fluidity of the ex oplasmic and the cytoplasmic leaflets of the erythrocyte membrane. Mor eover, as deduced from our previous investigations, the swelling behav iour of red blood cells could not be responsible for the observed effe ct. Possible mechanisms for the spectrin effect include a change in th e ability of the target membrane to bend locally, and a change in the rate of formation and development of the fusion pore.