An apical membrane complex controls rhoptry exocytosis and invasion in Toxoplasma

Abstract

Apicomplexan parasites possess secretory organelles called rhoptries that undergo regulated exocytosis upon contact with the host. This process is essential for the parasitic lifestyle of these pathogens and relies on an exocytic machinery sharing structural features and molecular components with free-living ciliates. Here, we performed a Tetrahymena-based transcriptomic screen to uncover novel exocytic factors in Ciliata and Apicomplexa. We identified membrane-bound proteins, named CRMPs, forming part of a large complex essential for rhoptry secretion and invasion in Toxoplasma. In contrast to previously described rhoptry exocytic factors, TgCRMPs are not required for the assembly of the rhoptry secretion machinery and only transiently associated with the exocytic site - prior to invasion. CRMPs and their partners contain putative host cell-binding domains, and CRMPa shares similarity to GPCR proteins. We propose that the CRMP complex acts as host-molecular sensor to ensure that rhoptry exocytosis occurs when the parasite contacts the host cell.

Functional Characterization of the Thrombospondin-Related Paralogous Proteins Rhoptry Discharge Factors 1 and 2 Unveils Phenotypic Plasticity in Toxoplasma gondii Rhoptry Exocytosis

“…The non-micronemal localization of RDF1 and RDF2 shown in the present work is further supported by spatial hyperLOPIT (Localization of Organelle Proteins by Isotopic Tagging) data ( Barylyuk et al, 2020 ), which demonstrated that RDF1 is part of a separate minicluster including another member of the thrombospondin family (TGME49_277910) and two multipass TM proteins (TGGT1_261080, TGGT1_292020) showing homology to the Plasmodium Cysteine-Repeat Modular Proteins ( Thompson et al, 2007 ; Douradinha et al, 2011 ). Interestingly, two recent studies deposited in a preprint repository ( Singer et al, 2022 ; Sparvoli et al, 2022 ) showed that TGGT1_261080 and TGGT1_292020 depletion impairs rhoptry discharge and that these two molecules are part of a multiprotein complex also including RDF1. These results support a model in which RDF1 and RDF2 play a key role as Coccidia-specific components of a protein complex acting as a sensor of parasite-host cell contact leading to rhoptry exocytosis.…”

Functional characterization of the thrombospondin-related paralogous proteins rhoptry discharge factor 1 and 2 unveils phenotypic plasticity in Toxoplasma gondii rhoptry exocytosis

“…The non micronemal localization of RDF1 and RDF2 shown in the present work is further supported by spatial hyperLOPIT (Localisation of Organelle Proteins by Isotopic Tagging) data (Barylyuk et al, 2020), which demonstrated that RDF1 is part of a separate minicluster including another member of the thrombospondin family (TGME49_277910) and two multipass TM proteins (TGGT1_261080, TGGT1_292020) showing homology to the Plasmodium Cysteine-Repeat Modular Proteins (Douradinha et al, 2011; Thompson et al, 2007). Interestingly, two recent studies deposited in a preprint repository (Singer et al, 2022; Sparvoli et al, 2022) showed that TGGT1_261080 and TGGT1_292020 depletion impairs rhoptry discharge and that these two molecules are part of a multiprotein complex also including RDF1. These results support a model in which RDF1 and RDF2 play a key role as Coccidia-specific components of a protein complex acting as a sensor of parasite-host cell contact leading to rhoptry exocytosis.…”

How Apicomplexa Parasites Secrete and Build Their Invasion Machinery

“…The conservation of the secretion process between Apicomplexa and Alveolata is not only restricted to the membrane fusion event; it also extends to the signaling events leading to exocytosis. Recent studies in T. gondii described membrane-bound proteins, named CRMPs (cysteine repeat modular proteins), as part of a large complex essential for rhoptry secretion and invasion (109,131,133). CRMPs are conserved in Tetrahymena and required for mucocyst release (133).…”

“…Recent studies in T. gondii described membrane-bound proteins, named CRMPs (cysteine repeat modular proteins), as part of a large complex essential for rhoptry secretion and invasion (109,131,133). CRMPs are conserved in Tetrahymena and required for mucocyst release (133). Unlike Nd proteins, T. gondii CRMPs are not required for assembly of the RSA and are only transiently associated with the exocytic site prior to invasion (133).…”

“…CRMPs are conserved in Tetrahymena and required for mucocyst release (133). Unlike Nd proteins, T. gondii CRMPs are not required for assembly of the RSA and are only transiently associated with the exocytic site prior to invasion (133). CRMPs and their partners contain putative host cell-binding domains, suggesting that they may act as molecular host sensors to ensure timely coordination of host cell contact and rhoptry exocytosis.…”