Endoplasmic Reticulum PI(3)P Lipid Binding Targets Malaria Proteins to the Host Cell

Center for Rare and Neglected Diseases, University of Notre Dame, Notre Dame, IN 46556, USA.
Cell (Impact Factor: 33.12). 01/2012; 148(1-2):201-12. DOI: 10.1016/j.cell.2011.10.051
Source: PubMed

ABSTRACT Hundreds of effector proteins of the human malaria parasite Plasmodium falciparum constitute a "secretome" carrying a host-targeting (HT) signal, which predicts their export from the intracellular pathogen into the surrounding erythrocyte. Cleavage of the HT signal by a parasite endoplasmic reticulum (ER) protease, plasmepsin V, is the proposed export mechanism. Here, we show that the HT signal facilitates export by recognition of the lipid phosphatidylinositol-3-phosphate (PI(3)P) in the ER, prior to and independent of protease action. Secretome HT signals, including those of major virulence determinants, bind PI(3)P with nanomolar affinity and amino acid specificities displayed by HT-mediated export. PI(3)P-enriched regions are detected within the parasite's ER and colocalize with endogenous HT signal on ER precursors, which also display high-affinity binding to PI(3)P. A related pathogenic oomycete's HT signal export is dependent on PI(3)P binding, without cleavage by plasmepsin V. Thus, PI(3)P in the ER functions in mechanisms of secretion and pathogenesis.

Download full-text


Available from: Kasturi Haldar, Dec 24, 2014
  • Source
    • "We investigated for host-cell targeting motifs RXLXE/D/Q (where X is a neutral or a hydrophobic amino acid residue) that were previously reported for their activity to export Plasmodium falciparum proteins from the intracellular parasites (Bhattacharjee et al., 2012) to the surrounding erythrocytes. We also searched for the presence of consensus sequences XBBXBX, XBBBXXBX and XBBBXXBBBXXBBX (where X is a neutral or hydrophobic amino acid residue and B is a basic amino acid residue ) which were implicated in hairpin binding (de Castro Cortes et al., 2012). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Orphan genes are protein coding genes that lack recognizable homologs in other organisms. These genes were reported to comprise a considerable fraction of coding regions in all sequenced genomes and thought to be allied with organism's lineage-specific traits. However, their evolutionary persistence and functional significance still remain elusive. Due to lack of homologs with the host genome and for their probable lineage-specific functional roles, orphan gene product of pathogenic protozoan might be considered as the possible therapeutic targets. L. major is an important parasitic protozoan of the genus Leishmania that is associated with the disease cutaneous leishmaniasis. Therefore, evolutionary and functional characterization of orphan genes in this organism may help in understanding the factors prevailing pathogen evolution and parasitic adaptation. In this study, we systematically identified orphan genes of L. major and employed several in-silico analyses for understanding their evolutionary and functional attributes. To trace the signatures of molecular evolution, we compared their evolutionary rate with non-orphan genes. In agreement with prior observations, here we noticed that orphan genes evolve at a higher rate as compared to non-orphan genes. Lower sequence conservation of orphan genes was previously attributed solely due to their younger gene age. However, here we observed that together with gene age, a number of genomic (like expression level, GC content, variation in codon usage) and proteomic factors (like protein length, intrinsic disorder content, hydropathicity) could independently modulate their evolutionary rate. We considered the interplay of all these factors and analyzed their relative contribution on protein evolutionary rate by regression analysis. On the functional level, we observed that orphan genes are associated with regulatory, growth factor and transport related processes. Moreover, these genes were found to be enriched with various types of interaction and trafficking motifs, implying their possible involvement in host-parasite interactions. Thus, our comprehensive analysis of L. major orphan genes provided evidence for their extensive roles in host-pathogen interactions and virulence. Copyright © 2015. Published by Elsevier B.V.
    Infection, genetics and evolution: journal of molecular epidemiology and evolutionary genetics in infectious diseases 04/2015; 32. DOI:10.1016/j.meegid.2015.03.031 · 3.26 Impact Factor
  • Source
    • "A recent systematic study in P. bergheiinfected erythrocytes identified 13 previously unrecognized PEXEL/HT proteins and PNEPs (Pasini et al., 2013), suggesting that other, and perhaps all, Plasmodium species export a large and diverse set of proteins to remodel the erythrocyte. The current data from asexual blood-stage parasites indicate that the PEXEL/HT-motif is cleaved by plasmepsin V in the parasite endoplasmic reticulum (Boddey et al., 2010; Russo et al., 2010), where the PEXEL/HTcontaining proteins are proposed to be recruited by binding to phosphatidylinositol 3-phosphate (PI3P) (Bhattacharjee et al., 2012). Identification of cleaved, N-acetylated peptides from PEXEL/HT proteins in stage I gametocytes indicates that this machinery is also active in the endoplasmic reticulum of gametocytes, an observation further supported by the fact that plasmepsin V is readily detectable in the proteomes of all asexual and sexual blood stages (Silvestrini et al., 2010). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Obligate intracellular pathogens actively remodel their host cells to boost propagation, survival, and persistence. Plasmodium falciparum, the causative agent of the most severe form of malaria, assembles a complex secretory system in erythrocytes. Export of parasite factors to the erythrocyte membrane is essential for parasite sequestration from the blood circulation and a major factor for clinical complications in falciparum malaria. Historic and recent molecular reports show that host cell remodeling is not exclusive to P. falciparum and that parasite-induced intra-erythrocytic membrane structures and protein export occur in several Plasmodia. Comparative analyses of P. falciparum asexual and sexual blood stages and imaging of liver stages from transgenic murine Plasmodium species show that protein export occurs in all intracellular phases from liver infection to sexual differentiation, indicating that mammalian Plasmodium species evolved efficient strategies to renovate erythrocytes and hepatocytes according to the specific needs of each life cycle phase. While the repertoire of identified exported proteins is remarkably expanded in asexual P. falciparum blood stages, the putative export machinery and known targeting signatures are shared across life cycle stages. A better understanding of the molecular mechanisms underlying Plasmodium protein export could assist in designing novel strategies to interrupt transmission between Anopheles mosquitoes and humans.
    Cellular Microbiology 12/2013; 16(3). DOI:10.1111/cmi.12251 · 4.82 Impact Factor
  • Source
    • "An amino-terminal hydrophobic signal peptide ensures the entry into the secretory pathway of the parasite by translocation into the endoplasmic reticulum (ER). Here, the PEXEL/VTS motif binds phosphatidylinositol 3-phosphate (PI3P) [13] prior to cleavage behind the leucine residue by the ER-resident protease plasmepsin V [14] [15]. The matured PEXEL/VTS protein becomes acetylated at its amino-terminus [16] and is now flagged for transposition across the PVM. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Protein export is considered an essential feature of malaria parasite blood stage development. Here, we examined five components of the candidate Plasmodium translocon of exported proteins (PTEX), a complex thought to mediate protein export across the parasitophorous vacuole membrane into the host cell. Using the murine malaria model parasite Plasmodium berghei, we succeeded in generating parasite lines lacking PTEX88 and thioredoxin 2 (TRX2). Repeated attempts to delete the remaining three translocon components failed, suggesting essential functions for EXP2, PTEX150, and heat shock protein 101 (HSP101) during blood stage development. To analyze blood infections of the null-mutants, we established a flow cytometry-assisted intravital competition assay using three novel high fluorescent lines (Bergreen, Beryellow, and Berred). Although blood stage development of parasites lacking TRX2 was affected, the deficit was much more striking in PTEX88 null-mutants. The multiplication rate of PTEX88-deficient parasites was strongly reduced resulting in out-competition by wild-type parasites. Endogenous tagging revealed that TRX2::tag resides in distinct punctate organelles of unknown identity. PTEX88::tag shows a diffuse intraparasitic pattern in blood stage parasites. In trophozoites, PTEX88::tag also localized to previously unrecognized extensions reaching from the parasite surface into the erythrocyte cytoplasm. Together, our results indicate auxiliary roles for TRX2 and PTEX88 and central roles for EXP2, PTEX150, and HSP101 during P. berghei blood infection.
    Molecular and Biochemical Parasitology 09/2013; 191(1). DOI:10.1016/j.molbiopara.2013.09.003 · 2.24 Impact Factor
Show more