Conducted jointly by CEA and UAC, this research spotlights the TgSORT receptor, a key to new antiparasitic therapies.
The Essentials: Conducted jointly by CEA and UAC, this research spotlights the TgSORT receptor, a key to new antiparasitic therapies.
Houévo Ariane Honfozo, researcher at I2BC; LBBM (Commissariat à l'énergie atomique et aux énergies alternatives).
Thesis defended in 2022 at the doctoral school Doctoral School of Structure and Dynamics of Living Systems (Gif-sur-Yvette, Essonne; 2015-....).
This research was carried out under a Franco-Beninese joint supervision (cotutelle), ensuring simultaneous grounding in local field realities and international academic standards.
Referenced in the ABES/STAR network, this thesis meets the rigor standards of French higher education.
Context and Research Question
Protozoan parasites of the Apicomplexa phylum, such as Toxoplasma gondii and Plasmodium falciparum, are responsible for serious diseases in humans and animals. T. gondii is implicated in toxoplasmosis, while P. falciparum is the leading cause of malaria, resulting in millions of cases and deaths each year. These organisms possess specific secretory organelles, micronemes and rhoptries, which are crucial for their invasion of host cells. In particular, TgSORT, a transmembrane cargo receptor, plays a decisive role in the biogenesis of these organelles. It is located in the post-Golgi and early endosome compartments and is responsible for sorting and maturing the proteins needed for parasitic invasion. Its homology with human sortilin, which is involved in lysosomal transport, raises questions about its functional role in T. gondii and P. falciparum.
Methodology
The research was carried out as part of a collaboration between the French Alternative Energies and Atomic Energy Commission (CEA) and the University of Abomey-Calavi (UAC). The project focused on studying the interactions between TgSORT and its ligands. To do so, the N-terminal domain (N-SORT) of TgSORT was expressed in Pichia pastoris, a yeast that allows better solubility compared with expression in E. coli. Interaction partners, such as MIC5, ROP18 and ROP16, were also expressed to study their binding with TgSORT.
Cryo-electron microscopy (cryo-EM) was used to determine the structure of N-SORT. This technique made it possible to observe the toric structure of N-SORT, confirmed by the 3D structure prediction model generated by the AlphaFold 2 algorithm. Automated screening tests were carried out on a transgenic strain of T. gondii (SORT-GFP/ROP1-mCherry) to identify compounds capable of altering the subcellular distribution of TgSORT.
Key Findings
The results obtained indicate that TgSORT is indispensable for the virulence and survival of T. gondii due to its role in the biogenesis of secretory organelles. Cryo-EM revealed that N-SORT has a toric structure, composed of 10 β-propeller domains arranged in a helix, followed by two 10CC motifs forming a central tunnel. Three loops were identified on the outside of this tunnel, suggesting potential sites for ligand interactions.
AlphaFold 2 made it possible to establish a direct link between N-SORT and rhoptry proteins, using motifs similar to those of human sortilin for binding neurotensin. Automated screening identified twelve positive compounds from a library of 1,121 molecules. Of these, four showed validated activity on P. falciparum 3D7, indicating that these small molecules could influence the subcellular distribution of TgSORT and, consequently, affect the parasite's virulence.
Discussion and Outlook
The work carried out in this thesis highlights the importance of TgSORT in the virulence of Apicomplexa. Knowledge of the interactions between TgSORT and its ligands, as well as the structural characteristics of N-SORT, opens new avenues for the development of antiparasitic therapies. The results obtained also underscore the relevance of automated screening approaches for identifying potential therapeutic compounds.
Integrating these discoveries into therapeutic strategies could enable the development of targeted treatments against T. gondii and P. falciparum infections. Collaboration between academic institutions and pharmaceutical companies will be crucial to translate these research results into clinical applications. Investment in research on TgSORT and parasitic invasion mechanisms is needed to strengthen response capacity to the health challenges posed by parasitic diseases worldwide.
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Sources and Access
Houévo Ariane Honfozo. Un récepteur unique et essentiel au Toxoplasma et au Plasmodium : de la structure-fonction vers de nouvelles stratégies thérapeutiques antiparasitaires. Biologie moléculaire. Université Paris-Saclay; Université d'Abomey-Calavi UAC (Bénin), 2022. Français. ⟨NNT : 2022UPASL089⟩. ⟨tel-04050149⟩