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MBC in Press, published online ahead of print July 6, 2005
Mol. Biol. Cell 10.1091/mbc.E05-04-0281

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Submitted on April 7, 2005
Accepted on June 23, 2005

Conditional Expression of Toxoplasma gondii Apical Membrane Antigen-1 (TgAMA1) Demonstrates That TgAMA1 Plays a Critical Role in Host Cell Invasion

Jeffrey Mital,* Markus Meissner,{dagger}{ddagger} Dominique Soldati,{dagger}{sect} and Gary E. Ward*

*Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, VT 05405; {dagger}Department of Biological Sciences, Imperial College London, SW72AZ London, United Kingdom

Monitoring Editor: Ralph Isberg

Toxoplasma gondii is an obligate intracellular parasite and an important human pathogen. Relatively little is known about the proteins that orchestrate host cell invasion by T. gondii or related apicomplexan parasites (including Plasmodium spp., which cause malaria), due to the difficulty of studying essential genes in these organisms. We have used a recently developed regulatable promoter to create a conditional knockout of T. gondii Apical Membrane Antigen-1 (TgAMA1). TgAMA1 is a transmembrane protein that localizes to the parasite’s micronemes, secretory organelles that discharge during invasion. AMA1 proteins are conserved among apicomplexan parasites and are of intense interest as malaria vaccine candidates. We show here that T. gondii tachyzoites depleted of TgAMA1 are severely compromised in their ability to invade host cells, providing direct genetic evidence that AMA1 functions during invasion. The TgAMA1 deficiency has no effect on microneme secretion or initial attachment of the parasite to the host cell, but it does inhibit secretion of the rhoptries, organelles whose discharge is coupled to active host cell penetration. The data suggest a model in which attachment of the parasite to the host cell occurs in two distinct stages, the second of which requires TgAMA1 and is involved in regulating rhoptry secretion.

Present addresses: {ddagger}Department of Parasitology, Hygiene-Institut, Universitatsklinikum Heidelberg, D-69120 Heidelberg, Germany; {sect}Department of Microbiology and Molecular Medicine, University of Geneva, 1211 Geneva 4, Switzerland.

Address correspondence to: Gary E. Ward (Gary.Ward{at}uvm.edu)




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