Apicomplexan parasites such as and export element (PEXEL) directs proteins into erythrocytes to remodel the host cell and establish infection. for targeting to the PV but the proteins have a reduced association with the PVM. Addition of a Myc tag before and after the cleavage site shows that processed HT/PEXEL protein has increased PVM association. These findings suggest that while and share comparable HT/PEXEL motifs HT/PEXEL made Ricasetron up of proteins interact with but do not cross the PVM. spp. and are obligate intracellular parasites of the phylum Apicomplexa that survive in a specialized membranous organelle known as the parasitophorous vacuole (PV). To invade and establish the PV sequentially discharges proteins from three secretory organelles – the micronemes rhoptries (ROP) and dense granules (1 2 The micronemes contain several adhesion proteins that allow the attachment of Ricasetron parasites to host cells (3). The rhoptries possess a series of virulence factors that differ between the three clonal linages of (4). Rhoptry proteins are also known to interact with microneme proteins to form a “moving junction” that migrates down the parasite (5 6 The dense granules secrete their contents (GRA proteins) to unique subcompartments of the PV where they contribute significantly to the biogenesis and modification of this compartment at the interface with the host cell (7 8 GRA proteins are important in maintaining the structures of the PV and potential nutrient acquisition (9). GRA15 is sufficient for host nuclear factor kappa B activation (10) and GRA1 GRA4 and GRA7 are effective antigens used in DNA vaccines (11 12 These findings demonstrate that secretory proteins play a significant role in host cell modulation and immune responses. Several targeting motifs to secretory organelles have been characterized. The pro-domains of microneme protein SUB1 and rhoptry protein ROP4 are sufficient to target a reporter protein to the micronemes or rhoptries respectively (13-15). Additional signals for microneme targeting include two tyrosine-based motifs SYHYY and EIEYE at the C-terminus of MIC2 (16). Targeting of the ROP2 family relies on both YXXφ and LL motifs within their cytoplasmic domains (13 17 For dense granule proteins Ricasetron it was thought that the transmission peptide is necessary and sufficient for localization to dense granules (18); however transmembrane-bearing GRA5 does not depend around the transmission peptide traffic to the dense granule (7). GRA5 is usually secreted as a soluble protein into the PV and becomes stably associated with the PVM (19). The N-terminal Ricasetron ectodomain of GRA5 and GRA6 mediate their dense granule targeting (7 20 suggesting that a sorting element is found within N-termini of certain GRA proteins. contains a sorting transmission sequence (RxLxE/Q/D) at the N-termini of proteins exported into the host cell (21 22 This sorting transmission called the host targeting (HT) or export element Ricasetron (PEXEL) motif facilitates export of proteins to the host cytosol where they remodel the host cytoskeleton to promote parasite survival (21 23 24 A similar RxLR-dEER motif was also discovered in secreted proteins of the Irish potato famine pathogen (25). Analyzing the genome with a clustering algorithm we discovered three unique polymorphic families that contain a HT/PEXEL-like motif near their N-terminus. One of these families is the previously characterized nucleoside triphosphate hydrolase (NTPase) family of GRA proteins (26). The other two families contain uncharacterized proteins annotated as hypothetical unknown. Our studies show that these hypothetical unknowns are new GRA proteins that localize to the PVM and PV. The HT/PEXEL motif serves as a cleavage signal and may contributes to protein-protein associations. HT/PEXEL containing proteins are not directed into the host cytosol which indicates a different trafficking mechanism between and genome was analyzed to identify protein families that: (i) contain an Rabbit polyclonal to AKAP13. ER-type transmission sequence (ii) are highly polymorphic as an indication that they have developed in response to antigenic pressure or functional diversification and (iii) contain a HT/PEXEL motif because this sequence is important for host targeting in the malaria parasite (examined in (24)). Here we characterize three protein families from this search (Table 1). One of the protein families (Family 1 Table 1) has been reported as NTPases which are GRA proteins. There.