Summary Obligate intracellular parasites must efficiently invade host cells in order to mature and be transmitted. For the malaria parasite Plasmodium falciparum, invasion of host red blood cells (RBCs) is essential. Here we describe a parasite-specific transcription factor PfAP2-I, belonging to the Apicomplexan AP2 (ApiAP2) family, that is responsible for regulating the expression of genes involved in RBC invasion. Our genome-wide analysis by ChIP-seq shows that PfAP2-I interacts with a specific DNA motif in the promoters of target genes. Although PfAP2-I contains three AP2 DNA-binding domains, only one is required for binding of the target genes during blood stage development. Furthermore, we find that PfAP2-I associates with several chromatin-associated proteins, including the Plasmodium bromodomain protein PfBDP1, and that complex formation is associated with transcriptional regulation. As a key regulator of red blood cell invasion, PfAP2-I represents a potential new antimalarial therapeutic target.

Numerous intracellular pathogens exploit cell surface glycoconjugates for host cell recognition and entry. Unlike bacteria and viruses, Toxoplasma gondii and other parasites of the phylum Apicomplexa actively invade host cells, and this process critically depends on adhesins (microneme proteins) released onto the parasite surface from intracellular organelles called micronemes (MIC). The microneme adhesive repeat (MAR) domain of T. gondii MIC1 (TgMIC1) recognizes sialic acid (Sia), a key determinant on the host cell surface for invasion by this pathogen. By complementation and invasion assays, we demonstrate that TgMIC1 is one important player in Sia-dependent invasion and that another novel Sia-binding lectin, designated TgMIC13, is also involved. Using BLAST searches, we identify a family of MAR-containing proteins in enteroparasitic coccidians, a subclass of apicomplexans, including T. gondii, suggesting that all these parasites exploit sialylated glycoconjugates on host cells as determinants for enteric invasion. Furthermore, this protein family might provide a basis for the broad host cell range observed for coccidians that form tissue cysts during chronic infection. Carbohydrate microarray analyses, corroborated by structural considerations, show that TgMIC13, TgMIC1, and its homologue Neospora caninum MIC1 (NcMIC1) share a preference for ␣2-3-over ␣2-6-linked sialyl-N-acetyllactosamine sequences. However, the three lectins also display differences in binding preferences. Intense binding of TgMIC13 to ␣2-9-linked disialyl sequence reported on embryonal cells and relatively strong binding to 4-O-acetylated-Sia found on gut epithelium and binding of NcMIC1 to 6sulfo-sialyl Lewis x might have implications for tissue tropism. Sialic acids (Sias)6 occur abundantly in glycoproteins and glycolipids on the cell surface and are exploited by many viruses and bacteria for attachment and host cell entry. Recognition of carbohydrates and in particular sialylated glycoconjugates is important also for host cell invasion by the Apicomplexa (1-4), a phylum that includes several thousand species of obligate intracellular parasites, among them the Plasmodium spp. causing malaria. Enteroparasitic coccidians are a subclass of Apicomplexa comprising Eimeria spp. responsible for coccidiosis in poultry, Neospora spp. causing neosporosis in cattle, and Toxoplasma, the causative agent of toxoplasmosis in warmblooded animals and humans.The host range and cell type targeted by these parasites vary widely across the phylum. Whereas Plasmodium falciparum merozoites exclusively invade erythrocytes of humans and great apes (5), Toxoplasma gondii tachyzoites (the form of the parasite associated with acute infection) invade an extremely broad range of cell types in humans and virtually all warmblooded animals, enabling rapid establishment of infection in the host and dissemination into deep tissues (6). Information is emerging on the involvement of carbohydrate-protein interactions in this broad host cell recognition (1).Many intracellular...

Lysine acetylation is a ubiquitous post-translational modification in many organisms including the malaria parasite Plasmodium falciparum, yet the full extent of acetylation across the parasite proteome remains unresolved. Moreover, the functional significance of acetylation or how specific acetyl-lysine sites are regulated is largely unknown. Here we report a seven-fold expansion of the known parasite ‘acetylome’, characterizing 2,876 acetylation sites on 1,146 proteins. We observe that lysine acetylation targets a diverse range of protein complexes and is particularly enriched within the Apicomplexan AP2 (ApiAP2) DNA-binding protein family. Using quantitative proteomics we determined that artificial perturbation of the acetate/acetyl-CoA balance alters the acetyl-lysine occupancy of several ApiAP2 DNA-binding proteins and related transcriptional proteins. This metabolic signaling could mediate significant downstream transcriptional responses, as we show that acetylation of an ApiAP2 DNA-binding domain ablates its DNA-binding propensity. Lastly, we investigated the acetyl-lysine targets of each class of lysine deacetylase in order to begin to explore how each class of enzyme contributes to regulating the P. falciparum acetylome.