Pathogenesis of Shigella diarrhoea: XVII- A mammalian cell membrane glycolipid, Gb₃, is required but sufficient to confirm sensitivity to shiga toxin

Abstract

Shiga toxin recognizesa galactose-α1 → 4-galactose terminal glycolipid,globotriaosylceramide (Gb₃), in sensitive mammalian cells and is translocated by endocytosis to the cytoplasm, where it blocks protein synthesis. To determine if Gb₃ is both required and sufficient for toxicity, Gb₃ content in cells was altered by blocking key biosynthetic or degradative path enzymes with specific inhibitors. The resulting decrease or increase in cellular Gb₃ was associated with a decrease or increase in binding of and response to Shiga toxin. Toxin-resistant Gb₃-deficient variants of sensitive cells fused with liposomes containing Gb₃ but not globotetraosylceramide (Gb₄) became susceptible, whereas fusion of Gb₃ liposomes to naturally resistant Gb₃-deficient CHD cells increased toxin binding but not cytotoxicity. These data demonstrate that Gb₃ is required, but not sufficient, for the action of Shiga toxin and suggest the existence of a toxin translocation mechanism linked to surface glycolipids that is not expressed in CHD cells.