Toxoplasma gondii: Molecular cloning and characterization of a novel 18-kDa secretory antigen, TSMIC10

Toxoplasma gondii: Molecular cloning and characterization of a novel 18-kDa secretory antigen, TgMIC10. Experimental Parasitology, 97, 77-88. During h ost cell invasion, Toxoplasma gondii secretes proteins from specialized org anelles (micronemes and rhoptries) located at the apical end of the parasit e. The contents of the micronemes appear to be crucial to T. gondii invasio n, as inhibition of microneme secretion prevents parasite entry into host c ells. Here we describe a new T. gondii microneme protein, TgMIC10. Molecula r characterization of a full-length TgMIC10 cDNA revealed that TgMIC10 lack s homology to any previously characterized proteins, although a homologue, NcMIC10, was identified in a closely related parasite, Neospora caninum. Tg MIC10 has an unusually long secretory leader sequence of 58 amino acids; th e mature TgMIC10 is 18 kDa, possesses nine diglutamic acid repeats and an i mperfect repeat sequence (RK(R/Y)HEEL), and is entirely devoid of cysteines . Antibodies raised against recombinant TgMIC10 recognized the native TgMIC 10 and localized the protein to the micronemes in indirect immunofluorescen ce and immunoEM experiments. Comparison of immunofluorescence images indica tes that TgMIC10 expression is higher in T. gondii tachyzoites, which are r esponsible for active infection, than in bradyzoites, which are responsible for latent infection. (C) 2001 Academic Press.