TgM2AP participates in Toxoplasma gondii host cells and is tightly associated with the invasion of adhesive protein TgMIC2

Like other members of the medically important phylum Apicomplexa, Toxoplasm a gondii is an obligate intracellular parasite that secretes several classe s of proteins involved in the active invasion of target host cells. Protein s in apical secretory organelles known as micronemes have been strongly imp licated in parasite attachment to host cells. TgMIC2 is a microneme protein with multiple adhesive domains that bind target cells and is mobilized ont o the parasite surface during parasite attachment. Here, we describe a nove l parasite protein, TgM2AP, which is physically associated with TgMIC2. TgM 2AP complexes with TgMIC2 within 15 min of synthesis and remains associated with TgMIC2 in the micronemes, on the parasite surface during invasion and in the culture medium after release from the parasite plasma membrane. TgM 2AP is proteolytically processed initially when its propeptide is removed d uring transit through the golgi and later while it occupies the parasite su rface after discharge from the micronemes. We show that TgM2AP is a member of a protein family expressed by coccidian parasites including Neospora can inum and Eimeria tenella. This phylogenic conservation and association with a key adhesive protein suggest that TgM2AP is a fundamental component of t he T. gondii invasion machinery.