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. As a first step in developing tools to study these processes, we show here that Clostridium septicum alpha-toxin, a pore-forming toxin that targets GPI-anchored protein receptors on the surface of mammalian cells, is active against T. gondii tachyzoites (50% effective concentration, 0.2 nM). Ultrastructural studies reveal that a tight physical connection between the plasma membrane and the underlying membranes of the inner membrane complex is locally disrupted by toxin treatment, resulting in a massive outward extension of the plasma membrane and ultimately lysis of the parasite. Toxin treatment also causes swelling of the parasite endoplasmic reticulum, providing the first direct evidence that alpha-toxin is a vacuolating toxin. Alpha-toxin binds to several parasite GPI-anchored proteins, including surface antigen 3 (SAG3) and SAG1. Interestingly, differences in the toxin-binding profiles between the virulent RH and avirulent P strain were observed. Alpha-toxin may prove to be a powerful experimental tool for molecular genetic analysis of GPI anchor biosynthesis and GPI-anchored protein trafficking in T. gondii and other susceptible protozoa.
Department of Microbiology and Molecular Genetics, University of Vermont, Burlington 05405, USA.
Michael J
MJ
Wichroski
Jody A
JA
Melton
Carolyn G
CG
Donahue
Rodney K
RK
Tweten
Gary E
GE
Ward
D000818:Animals; D000953:Antigens, Protozoan; D001427:Bacterial Toxins / Q000378:metabolism / Q000494:pharmacology*; D017261:Glycosylphosphatidylinositols / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D052899:Pore Forming Cytotoxic Proteins; D015800:Protozoan Proteins / Q000378:metabolism*; D014122:Toxoplasma / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D014617:Vacuoles
D000953:Antigens, Protozoan; D001427:Bacterial Toxins; D017261:Glycosylphosphatidylinositols; D008562:Membrane Glycoproteins; D052899:Pore Forming Cytotoxic Proteins; D015800:Protozoan Proteins; C047168:SAG1 antigen, Toxoplasma; C087692:SAG3 protein, Toxoplasma gondii; C064270:hemolytic toxin, Clostridium septicum; C032676:aerolysin