Clostridium septicum alpha toxin uses glycosylphosphatidylinositol-anchored protein receptors

The alpha toxin produced by Clostridium septicum is a channel-forming prote in that is an important contributor to the virulence of the organism. Chine se hamster ovary (CHO) cells are sensitive to low concentrations of the tox in, indicating that they contain toxin receptors. Using retroviral mutagene sis, a mutant CHO line (BAG15) was generated that is resistant to alpha tox in. FACS analysis showed that the mutant cells have lost the ability to bin d the toxin, indicating that they lack an alpha toxin receptor. The mutant cells are also resistant to aerolysin, a channel-forming protein secreted b y Aeromonas spp., which is structurally and functionally related to alpha t oxin and which is known to bind to glycosylphosphatidylinositol (GPI)-ancho red proteins, such as Thy-1. We obtained evidence that the BAG15 cells lack N-acetylglucosaminyl-phosphatidylinositol deacetylase-L, needed for the se cond step in GPI anchor biosynthesis, Several lymphocyte cell lines lacking GPI-anchored proteins were also shown to be less sensitive to alpha toxin. On the other hand, the sensitivity of CHO cells to alpha toxin was increas ed when the cells were transfected with the GPI-anchored folate receptor. W e conclude that alpha toxin, like aerolysin, binds to GPI-anchored protein receptors. Evidence is also presented that the two toxins bind to different subsets of GPI-anchored proteins.