SUMMARYGoose erythrocyte membranes were isolated and tested for their ability to compete with red cell receptors for vesicular stomatitis virus (VSV) attachment and fusion at acidic pH. Crude membranes, solubilized with Triton X-100, Tween 80 and octyl-/~-Dglucopyranoside, showed a dose-dependent inhibitory effect on virus binding and haemolysis. The chemical nature of the active molecules was investigated by enzyme digestion and by separation of purified components. Only the lipid moiety, specifically phospholipid and glycolipid, was found to inhibit VSV attachment; a more detailed analysis of these molecules showed that phosphatidylinositol, phosphatidylserine and GM3 ganglioside were responsible for the inhibitory activity and could therefore represent VSV binding sites on goose erythrocyte membranes. Removal of negatively charged groups from these molecules by enzymic treatment significantly reduced their activity, suggesting that electrostatic interactions play an important role in the binding of VSV to the cell surface. Enzymic digestion of whole erythrocytes confirmed the involvement of membrane lipid molecules in the cell surface receptor for VSV.
SUMMARYThe role of gangliosides in rabies virus infection of chick embryo-related (CER) cells was investigated. Cultured cells were pretreated with neuraminidase to render the cells transiently non-susceptible to viral infection. Incubation of these desialylated cells with gangliosides allowed them to incorporate exogenous gangliosides and they recovered their susceptibility to rabies virus infection. Infection of CER cells was monitored by specific fluorescence 24 h after virus inoculation. The use of individual purified gangliosides or mixtures of two gangliosides to restore cellular susceptibility to viral infection showed that GTlb and GQlb were the most effective. The disialogangliosides were also active, principally GD 1 b, whereas GM 1, GM3 were poorly active and GD3 inactive. Incubation of rabies virus with gangliosides prior to virus infection reduced the percentage of infected cells. The results indicate that highly sialylated gangliosides are part of the cellular membrane receptor structure for the attachment of infective rabies virus. However, it is possible that other glycoconjugates such as glycoproteins or glycolipids also participate as components of a receptor structure for rabies virus.
Binding of the non‐ionic detergent [3H]Triton X‐100 by tetanus toxin, by its fragment C and by its a chain has been studied. At pH 4.00 or above, tetanus toxin does not bind Triton X‐100. At pH lower than 4.00, binding of detergent to the toxin occurs. At pH 3.00, a maximum of 100 mol bound/mol of protein is reached only when the detergent concentration exceeds its critical micelle concentration. No measurable amount of Triton X‐100 is bound by the toxin C fragment at pH 3.00. Most of the tetanus toxin α chain precipitates out in Triton X‐100 at pH 3.00. Leakage of K+ from single‐walled asolectin vesicles loaded with potassium was observed with tetanus toxin at pH lower than 4.00. When ganglioside GDlb was present on the asolectin vesicles, release of K+ was obtained with tetanus toxin between pH 4.00 to 5.00. We suggest that, as for diphtheria toxin, entry of tetanus toxin into an acidic compartment of target cells might be required for the expression of its biological activity.
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