GM1 structure determines SV40-induced membrane invagination and infection

Abstract

Incoming simian virus 40 (SV40) particles enter tight-fitting plasma membrane invaginations after binding to the carbohydrate moiety of GM1 gangliosides in the host cell plasma membrane through pentameric VP1 capsid proteins. This is followed by activation of cellular signalling pathways, endocytic internalization and transport of the virus via the endoplasmic reticulum to the nucleus. Here we show that the association of SV40 (as well as isolated pentameric VP1) with GM1 is itself sufficient to induce dramatic membrane curvature that leads to the formation of deep invaginations and tubules not only in the plasma membrane of cells, but also in giant unilamellar vesicles (GUVs). Unlike native GM1 molecules with long acyl chains, GM1 molecular species with short hydrocarbon chains failed to support such invagination, and endocytosis and infection did not occur. To conceptualize the experimental data, a physical model was derived based on energetic considerations. Taken together, our analysis indicates that SV40, other polyoma viruses and some bacterial toxins (Shiga and cholera) use glycosphingolipids and a common pentameric protein scaffold to induce plasma membrane curvature, thus directly promoting their endocytic uptake into cells.

Lipid-Mediated Endocytosis

“…Only GM1 molecules with long alkyl chains support partitioning of virus with the liquid-ordered phase in vitro, and thus promote local enrichment of virion-receptor complexes (Ewers et al 2010). Studies using GM1 supplementation into mutant cells that do not contain glycosphingolipids of their own have, moreover, shown that although GM1 supports SV40 binding independently of its hydrocarbon chains, only those with long and preferably saturated alkyl chains promote association with the liquid-ordered phase (Ewers et al 2010). Unlike GM1 with short alkyl chains, they also allow endocytosis and infection.…”

“…The spacing of glycosphingolipid binding sites may be important given that the 30 Å distance is virtually identical in the polyomaviruses and the pentamer-containing toxins. In antibodies, the two binding sites are arranged flexible to one another and antibodies to GM1 indeed fail to induce lateral segregation of membranes (Ewers et al 2010). …”

“…Furthermore, after binding to the PM of cells, CTX, STX, and SV40 are found to associate with detergentresistant membranes (DRM) (Falguieres et al 2001;Wolf et al 2002;Damm et al 2005). Both intact SV40 particles and isolated VP1 pentamers cluster when bound to GM1 in artificial membranes (Ewers et al 2010). If such membranes have liquid-ordered and liquid-disordered phases, they accumulate in the liquid-ordered membrane (Ewers et al 2010).…”

“…Both intact SV40 particles and isolated VP1 pentamers cluster when bound to GM1 in artificial membranes (Ewers et al 2010). If such membranes have liquid-ordered and liquid-disordered phases, they accumulate in the liquid-ordered membrane (Ewers et al 2010).…”

Endocytose sans clathrine

“…Enfin, on sait désormais que le ganglioside GM1, récepteur lipidique enrichi dans les cavéoles, mais présent également dans d'autres microdomaines lipidiques et dans les puits à clathrine [11], est suffisant pour l'entrée de SV40 dans la cellule. La liaison d'un pentamère de la protéine VP1, formant la capside du virus, aux GM1 à chaînes acylées longues induit la formation d'invaginations membranaires, puis l'endocytose de la particule virale par une voie d'endocytose différente que nous décrirons plus loin [20]. signalisation, bien que cette propriété soit néanmoins controversée par des travaux récents [12].…”