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  Director : BRAUN-BRETON Catherine (cbb@pasteur.fr)


  abstract

 

  • Enzymes involved in the entry of the parasite into and its exit from the erythrocyte- Catherine Braun-Breton (cbb@pasteur.fr) Chef de Laboratoire Institut Pasteur
  • Proteins trafficking in P. falciparum - Denise Mattei (dmm@pasteur.fr) Chef de Laboratoire Institut Pasteur
  • Genomic plasticity and variant erythrocyte surface molecules of P. falciparum - Artur Scherf (ascherf@pasteur.fr), Directeur de Recherche (1ère classe) au CNRS



  report

cale

The unit is composed of three laboratories headed by C. Braun-Breton, D. Mattei and A. Scherf, respectively. The studies carried out in the unit concern the protozoan parasite Plasmodium and essentially the species P. falciparum, which is responsible for the most serious cases of malaria in humans. We are interested in the interaction between this parasite and its host cell, the red blood cell or erythrocyte, and the interactions between infected erythrocytes and other cells of the host, such as endothelial cells. The main aim of the unit is to increase our understanding of the mechanisms associated with biological functions crucial to the development of the parasite in mammalian hosts, such as invasion of the host cell, the modifications to the host cell induced by the intracellular parasite, the maintenance of integrity and the generation of diversity in the parasite genome.

Enzymes involved in the entry of the parasite into and its exit from the erythrocyte

Catherine Braun-Breton (cbb@pasteur.fr) Chef de Laboratoire Institut Pasteur

We are interested in characterisation of the molecular processes underlining the release of infectious merozoite and the entry of these merozoites into the red blood cell. Two approaches should allow us to better characterize crucial enzymes of these processes:

1. A proteomic study of secretory compartments of P. falciparum involved in the invasion of erythrocytes or release of merozoites. This study should enable us to determine which proteins constitute these compartments. In particular, we are seeking to identify enzyme activities crucial for these keysteps in parasite development, which could be the targets of specific inhibitors with antimalarial activity.

2. The molecular and functional characterization of two serine proteases that we have previously shown to be implicated. We are particularly interested in characterisation of the parasite serine protease responsible for the last step in the processing of MSP1 (the major surface protein of merozoites), which is essential for the entry of the parasite into the erythrocyte. Our work suggests that this processing is carried out by the product of the sub2 gene, which we have recently characterised in P. falciparum, P. vivax and in a species of Plasmodium that infects rodents, P. berghei. In collaboration with the laboratory of A. Waters (Leiden, the Netherlands) and using parasite transgenesis, we have shown that sub2 is a gene essential for the erythrocyte cycle of Plasmodium. Finally, we have developed tools for the determination of SUB2 activity. In collaboration with the laboratory of Jean Martinez (Montpellier University), we are developing specific inhibitors of PfSUB2 and of another parasite serine protease, Pfgp76, which we have shown to be involved in the entry of the parasite into red blood cells. Inhibitors active against this enzyme and that block the invasion of erythrocytes at nanomolar concentrations have recently been obtained.

The Maurer's clefts constitute a parasite secretory compartment within the cytoplasm of the host cell, translocating parasite proteins to the red cell membrane. We are currently studying molecular interactions between this comparment and the erythrocyte plasma membrane, involving the parasite Maurer's cleft protein PfSBP1 and the red cell membrane protein P40. Genetic manipulations of the Pfsbp1 gene have been initiated to precise the role of this interaction for the parasite development into the red cell.

Proteins trafficking in P. falciparum

Denise Mattei (dmm@pasteur.fr) Chef de Laboratoire Institut Pasteur

"Knobs", protuberances resulting from modifications to the erythrocyte membrane induced by the parasite, are observed at points of adhesion to endothelial cells and are involved in the phenomenon of parasite sequestration. Several proteins of parasite origin are present in the "knobs": PfHRPI (Histidine-Rich Protein I), the major structural component, and the variant antigen PfEMP1 (Erythrocyte Membrane Protein 1). We found that the transport of PfHRPI seemed to be insensitive to the action of BFA. The C-terminal extremity of PfHRPI presents a potential isoprenylation site preceded by a sequence of several basic amino acids. The association of these two motifs constitutes a signal for targeting to the plasma membrane and may mediate the secretion of PfHRPI into the cytoplasm of the red blood cell. We also showed that identical clag9 genes are expressed in both CSA and CD36-selected parasite populations. Thus, our data do not support the previously proposed role of CLAG9 in mediating adhesion to CD36. Rather, CLAG9 could have an accessory function for PfEMP1 molecules during transport or form a PfEMP1 CLAG9 complex at the red blood cell surface. Our recent co-localisation studies with several secreted proteins in BFA-treated parasites suggest that the ER is composed of different domains. It is possible that the properties of the polypeptides, such as their solubility or affinity for membranes, determine their ‘compartmentalisation'. Our result suggest that the targeting of P. falciparum proteins to the various compartments of the infected erythrocyte begins within the ER. Characterisation of the secretion pathways specific to the parasite may lead to the identification of new targets of potential importance for the development of drugs active against the adhesion phenotype of parasitised erythrocytes.

Genomic plasticity and variant erythrocyte surface molecules of P. falciparum

Artur Scherf (ascherf@pasteur.fr), Directeur de Recherche (1ère classe) au CNRS

A major line of research in our laboratory is the investigation of parasite-encoded variant adhesion molecules which are inserted into the erythrocyte membrane during the intracellular blood stage development. Sequestration of infected erythrocytes (IE) in different organs is probably a key event in malaria pathogenesis. The principal molecule mediating IE adhesion and antigenic variation is P. falciparum erythrocyte membrane protein 1(PfEMP1), encoded by the polymorphic var gene family. We have identified the chondroitin sulfate A (CSA) binding domain of the varCSA gene and are investigating its potential for new intervention strategies to protect women during pregnancy from disease. Recently, in collaboration with Dr. Gysin we have described the CSA-independent cytoadhesion of ring-stage IE presumably mediated by two parasite derived proteins on the surface of ring-infected erythrocytes called ring suface protein 1 and 2 (RSP1 and RSP2). This suggests that non-circulating (cryptic) parasite subpopulations are present in malaria patients. We have started to identify the genes that code for RSP1 and RSP2 which are potential target molecules for the development of new intervention strategies.

New data on the organization of plasmodial telomeres has been recently obtained in our laboratory. Telomeres form clusters of 4 to 7 heterologous chromosome ends at the nuclear periphery in asexual and sexual parasite stages. This subnuclear compartment promotes gene conversion between members of subtelomeric virulence factor genes (var, possibly rif and other's) in heterologous chromosomes resulting in diversity of antigenic and adhesive phenotypes. This has important implications for parasite survival. Furthermore, we have been studying different aspects of telomere biology of malaria parasites. Plasmodial telomerase activity has been detected in protein cell extracts. A candidate for the P. falciparum telomerase catalytic subunit has been identified in the genome database. Knock out experiments are in process to verify that this is an essential gene for the survival of the parasite and can be considered as a new target for the development of anti-parasite therapies.



  publications

puce Publications of the unit on Pasteur's references database


  personnel

  Office staff Researchers Scientific trainees Other personnel
 

LOZNER Josyane

BRAUN-BRETON Catherine

MATTEI Denise

SCHERF Artur - Directeur de Recherche

BARALE Jean Christophe

BERRY Laurence

FIGUEIREDO Luisa

FREITAS Lucio Jr

PIRRIT Lindsay

STERKERS Yvon

THOMAS Virginie

UZUREAU Pierrick

VINCENSINI Laetitia

BLISNICK Thierry

SCHEIDIG-BENATAR Christine


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