The identification and structure of the membrane-spanning domain of the Clostridium septicum alpha toxin.

Alpha toxin (AT) is a pore-forming toxin produced by Clostridium septicum that belongs to the unique aerolysin-like family of pore-forming toxins. The location and structure of the transmembrane domains of these toxins have remained elusive. Using deletion mutagenesis, cysteine-scanning mutagenesis and multiple spectrofluorimetric methods a membrane-spanning amphipathic beta-hairpin of AT has been identified.

Clostridium septicum alpha-toxin is active against the parasitic protozoan Toxoplasma gondii and targets members of the SAG family of glycosylphosphatidylinositol-anchored surface proteins.

As is the case with many other protozoan parasites, glycosylphosphatidylinositol (GPI)-anchored proteins dominate the surface of Toxoplasma gondii tachyzoites. The mechanisms by which T. gondii GPI-anchored proteins are synthesized and transported through the unusual triple-membrane structure of the parasite pellicle to the plasma membrane remain largely unknown.