An unconventional SNARE complex mediates exocytosis at the plasma membrane and vesicular fusion at the apical annuli in Toxoplasma gondii

Identification a novel syntaxin-like protein from silkworm Bombyx mori pathogen Nosema bombycis and characteristics its membrane fusion function

Pebrine is a serious disease of the silkworm, Bombyx mori, caused by the first identified microsporidium Nosema bombycis, which is an obligate parasitic single-celled eukaryote. The pathogen can spread both horizontally and vertically, severely affecting sericulture. SNARE proteins mainly mediate the transport of vesicles and membrane fusion, playing a key role in the biological processes. The microsporidium is known to have a well-developed membrane system, especially the polaroplast which occupies most of the volume of mature spores. In order to explore the function of microsporidian SNARE protein, the transcription and subcellular localization characteristics of a novel Syntaxin-like protein (NbSTX-like) from N. bombycis that had a conserved t-SNARE motif were analyzed. In the different development stages of N. bombycis, the NbSTX-like expressed in the nucleus of meronts, then transited to the cytoplasm in the sporonts, gradually gathered at the two ends of the sporoblasts, and finally concentrated at the polaroplast, posterior vacuole and plasma membrane region of mature spores. Interestingly, the rNbSTX-like protein could fuse liposomes to form large vesicular and tubular structures. The formation of sporoplasms was inhibited by the anti-NbSTX-like serum, implying that NbSTX-like protein participated in sporoplasm maturation. These findings laid a foundation for studying the function of SNARE proteins in microsporidia and provided new insights for the prevention and control of sericulture pathogens.

Toxoplasma gondii C2 Domain Protein Deletion Mutant as a Promising Vaccine Against Toxoplasmosis in Mice

Toxoplasma gondii (T. gondii), a parasitic protozoan capable of infecting nearly all warm-blooded animals, causes significant economic losses in livestock and poses a significant threat to both animal and public health. Despite its impact, no ideal vaccine is currently available to prevent toxoplasmosis. Vesicular transport plays a crucial role in the life cycle of T. gondii, and proteins involved in this process - such as those containing C2 domains - may serve as novel targets for the development of live attenuated vaccines. In this study, we evaluated the feasibility of a C2 domain-containing protein (TGME49_203240) as a live attenuated vaccine candidate. Our findings suggest that TGME49_203240 may be involved in vesicular transport and that it is essential for T. gondii growth. Deletion of TGME49_203240 reduced parasite virulence and impaired tissue cyst formation in mice. Moreover, mice vaccinated with ME49Δ203240 were protected against the lethal challenge of the tachyzoites of T. gondii I, II, III strains and cysts of II strain. In addition, the ME49Δ203240 strain elicited robust immune responses, including the production of high levels of specific IgG antibodies and key cytokines (IFN-γ, TNF-α and IL-12). These findings highlight TGME49_203240 as a promising target for the development of a live attenuated vaccine against T. gondii.

Transient Adaptation of Toxoplasma gondii to Exposure by Thiosemicarbazone Drugs That Target Ribosomal Proteins Is Associated with the Upregulated Expression of Tachyzoite Transmembrane Proteins and Transporters

Thiosemicarbazones and their metal complexes have been studied for their biological activities against bacteria, cancer cells and protozoa. Short-term in vitro treatment with one gold (III) complex (C3) and its salicyl-thiosemicarbazone ligand (C4) selectively inhibited proliferation of T. gondii. Transmission Electron Microscopy (TEM) detected transient structural alterations in the parasitophorous vacuole membrane and the tachyzoite cytoplasm, but the mitochondrial membrane potential appeared unaffected by these compounds. Proteins potentially interacting with C3 and C4 were identified using differential affinity chromatography coupled with mass spectrometry (DAC-MS). Moreover, long-term in vitro treatment was performed to investigate parasitostatic or parasiticidal activity of the compounds. DAC-MS identified 50 ribosomal proteins binding both compounds, and continuous drug treatments for up to 6 days caused the loss of efficacy. Parasite tolerance to both compounds was, however, rapidly lost in their absence and regained shortly after re-exposure. Proteome analyses of six T. gondii ME49 clones adapted to C3 and C4 compared to the non-adapted wildtype revealed overexpression of ribosomal proteins, of two transmembrane proteins involved in exocytosis and of an alpha/beta hydrolase fold domain-containing protein. Results suggest that C3 and C4 may interfere with protein biosynthesis and that adaptation may be associated with the upregulated expression of tachyzoite transmembrane proteins and transporters, suggesting that the in vitro drug tolerance in T. gondii might be due to reversible, non-drug specific stress-responses mediated by phenotypic plasticity.

Moniezia benedeni drives the SNAP-25 expression of the enteric nerves in sheep's small intestine

BACKGROUND

The neuroimmune network plays a crucial role in regulating mucosal immune homeostasis within the digestive tract. Synaptosome-associated protein 25 (SNAP-25) is a presynaptic membrane-binding protein that activates ILC2s, initiating the host's anti-parasitic immune response.

METHODS

To investigate the effect of Moniezia benedeni (M. benedeni) infection on the distribution of SNAP-25 in the sheep's small intestine, the recombinant plasmid pET-28a-SNAP-25 was constructed and expressed in BL21, yielding the recombinant protein. Then, the rabbit anti-sheep SNAP-25 polyclonal antibody was prepared and immunofluorescence staining was performed with it. The expression levels of SNAP-25 in the intestines of normal and M. benedeni-infected sheep were detected by ELISA.

RESULTS

The results showed that the SNAP-25 recombinant protein was 29.3 KDa, the titer of the prepared immune serum reached 1:128,000. It was demonstrated that the rabbit anti-sheep SNAP-25 polyclonal antibody could bind to the natural protein of sheep SNAP-25 specifically. The expression levels of SNAP-25 in the sheep's small intestine revealed its primary presence in the muscular layer and lamina propria, particularly around nerve fibers surrounding the intestinal glands. Average expression levels in the duodenum, jejunum, and ileum were 130.32 pg/mg, 185.71 pg/mg, and 172.68 pg/mg, respectively. Under conditions of M. benedeni infection, the spatial distribution of SNAP-25-expressing nerve fibers remained consistent, but its expression level in each intestine segment was increased significantly (P < 0.05), up to 262.02 pg/mg, 276.84 pg/mg, and 326.65 pg/mg in the duodenum, jejunum, and ileum, and it was increased by 101.06%, 49.07%, and 89.16% respectively.

CONCLUSIONS

These findings suggest that M. benedeni could induce the SNAP-25 expression levels in sheep's intestinal nerves significantly. The results lay a foundation for further exploration of the molecular mechanism by which the gastrointestinal nerve-mucosal immune network perceives parasites in sheep.

Apical annuli are specialised sites of post-invasion secretion of dense granules in Toxoplasma

Apicomplexans are ubiquitous intracellular parasites of animals. These parasites use a programmed sequence of secretory events to find, invade, and then re-engineer their host cells to enable parasite growth and proliferation. The secretory organelles micronemes and rhoptries mediate the first steps of invasion. Both secrete their contents through the apical complex which provides an apical opening in the parasite's elaborate inner membrane complex (IMC) - an extensive subpellicular system of flattened membrane cisternae and proteinaceous meshwork that otherwise limits access of the cytoplasm to the plasma membrane for material exchange with the cell exterior. After invasion, a second secretion programme drives host cell remodelling and occurs from dense granules. The site(s) of dense granule exocytosis, however, has been unknown. In Toxoplasma gondii, small subapical annular structures that are embedded in the IMC have been observed, but the role or significance of these apical annuli to plasma membrane function has also been unknown. Here, we determined that integral membrane proteins of the plasma membrane occur specifically at these apical annular sites, that these proteins include SNARE proteins, and that the apical annuli are sites of vesicle fusion and exocytosis. Specifically, we show that dense granules require these structures for the secretion of their cargo proteins. When secretion is perturbed at the apical annuli, parasite growth is strongly impaired. The apical annuli, therefore, represent a second type of IMC-embedded structure to the apical complex that is specialised for protein secretion, and reveal that in Toxoplasma there is a physical separation of the processes of pre- and post-invasion secretion that mediate host-parasite interactions.