Activation of purified simian virus 40 virions by free amino-group containing phospholipid liposomes

Abstract

The infectivity of the simian virus 40 (SV40) virions purified after treatment with sodium deoxycholate is activated by mixing, prior to infection, the virions with the liposomes composed of phosphatidylserine or a mixture of phosphatidylethanolamine and phosphatidylcholine ( H. Shimura, and G. Kimura (1985), Virology 144, 268–272). The sucrose-CsCl cushion sedimentation analysis of the virions mixed with the liposomes revealed that the density of the radiolabeled virions became lower and that of the radiolabeled liposomes became higher to give a similar range, suggesting the binding of virions with the liposomes. Electron microscopy revealed the side-to-side association of virions with liposomes. The efficiency of adsorption of the virions to monkey kidney BSC-1 cells varied depending on phospholipid types mixed with virions and did not always become high. In the case of phosphatidylethanolamine liposomes, the free amino group in the phospholipid molecule was essential for the activation of the virion infectivity, because mono- and di-methylated phosphatidylethanolamine failed to activate the infectivity. Fluid nature of phospholipids seemed to be necessary also for the infectivity activation, because dipalmitoyl and distearoyl phospholipids did not activate virion infectivity at 37°, the temperature at which the liposomes of these phospholipids are supposed to be in a solid state. Presence of free amino groups and difference in acyl groups of the phospholipids did not influence the adsorption of the virions to cells. These results suggest that events which occur after adsorption of virions to cells are responsible for the activation of the SV40 virion infectivity by the liposomes composed of free amino-group containing phospholipids.